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LT1761 Datasheet

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Datasheet

LT1761 Series
1
1761sff
TYPICAL APPLICATION
DESCRIPTION
100mA, Low Noise,
LDO Micropower
Regulators in TSOT-23
The LT
®
1761 series are micropower, low noise, low
dropout regulators. With an external 0.01μF bypass
capacitor, output noise drops to 20μVRMS over a 10Hz to
100kHz bandwidth. Designed for use in battery-powered
systems, the low 20μA quiescent current makes them an
ideal choice. In shutdown, quiescent current drops to less
than 0.1μA. The devices are capable of operating over an
input voltage from 1.8V to 20V, and can supply 100mA of
output current with a dropout voltage of 300mV. Quiescent
current is well controlled, not rising in dropout as it does
with many other regulators.
The LT1761 regulators are stable with output capacitors as
low as 1μF. Small ceramic capacitors can be used without
the series resistance required by other regulators.
Internal protection circuitry includes reverse battery
protection, current limiting, thermal limiting and reverse
current protection. The device is available in fi xed output
voltages of 1.2V, 1.5V, 1.8V, 2V, 2.5V, 2.8V, 3V, 3.3V and
5V, and as an adjustable device with a 1.22V reference
voltage. The LT1761 regulators are available in the 5-lead
TSOT-23 package.
5V Low Noise Regulator
FEATURES
APPLICATIONS
n Low Noise: 20μVRMS (10Hz to 100kHz)
n Low Quiescent Current: 20μA
n Wide Input Voltage Range: 1.8V to 20V
n Output Current: 100mA
n Very Low Shutdown Current: <0.1μA
n Low Dropout Voltage: 300mV at 100mA
n Fixed Output Voltages: 1.2V, 1.5V, 1.8V, 2V, 2.5V,
2.8V, 3V, 3.3V, 5V
n Adjustable Output from 1.22V to 20V
n Stable with 1μF Output Capacitor
n Stable with Aluminum, Tantalum or
Ceramic Capacitors
n Reverse-Battery Protected
n No Reverse Current
n No Protection Diodes Needed
n Overcurrent and Overtemperature Protected
n Available in Tiny 5-Lead TSOT-23 Package
n Cellular Phones
n Pagers
n Battery-Powered Systems
n Frequency Synthesizers
n Wireless Modems
10Hz to 100kHz Output Noise
IN
SHDN
0.01μF 10μF
1761 TA01
OUT
VIN
5.4V TO
20V BYP
GND
LT1761-5
5V AT100mA
20μVRMS NOISE
F +VOUT
100μV/DIV 20μVRMS
1761 TA01b
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
LT1761 Series
2
1761sff
IN Pin Voltage .........................................................±20V
OUT Pin Voltage ......................................................±20V
Input to Output Differential Voltage .........................±20V
ADJ Pin Voltage ...................................................... ±7V
BYP Pin Voltage .....................................................±0.6V
SHDN Pin Voltage ................................................. ±20V
(Note 1)
ABSOLUTE MAXIMUM RATINGS
5 OUT
4 ADJ
IN 1
GND 2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
BYP 3
TJMAX = 150°C, θJA = 250°C/W
SEE APPLICATIONS INFORMATION SECTION
5 OUT
4 ADJ
IN 1
GND 2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
SHDN 3
TJMAX = 150°C, θJA = 250°C/W
SEE APPLICATIONS INFORMATION SECTION
5 OUT
4 BYP
IN 1
GND 2
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
SHDN 3
TJMAX = 150°C, θJA = 250°C/W
SEE APPLICATIONS INFORMATION SECTION
PIN CONFIGURATION
Output Short-Circuit Duration ........................ Indefi nite
Operating Junction Temperature Range
E, I Grade (Note 2) ............................. –40°C to 125°C
MP Grade (Note 2) ............................. –55°C to 125°C
Storage Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
LEAD FREE FINISH TAPE AND REEL PART MARKING * PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1761ES5-BYP#PBF LT1761ES5-BYP#TRPBF LTGC 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-BYP#PBF LT1761IS5-BYP#TRPBF LTGC 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-SD#PBF LT1761ES5-SD#TRPBF LTGH 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-SD#PBF LT1761IS5-SD#TRPBF LTGH 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.2#PBF LT1761ES5-1.2#TRPBF LTCDS 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.2#PBF LT1761IS5-1.2#TRPBF LTCDS 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.5#PBF LT1761ES5-1.5#TRPBF LTMT 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.5#PBF LT1761IS5-1.5#TRPBF LTMT 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.8#PBF LT1761ES5-1.8#TRPBF LTJM 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.8#PBF LT1761IS5-1.8#TRPBF LTJM 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-1.8#PBF LT1761MPS5-1.8#TRPBF LTDCH 5-Lead Plastic TSOT-23 –55°C to 125°C
LT1761ES5-2#PBF LT1761ES5-2#TRPBF LTJE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2#PBF LT1761IS5-2#TRPBF LTJE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-2.5#PBF LT1761ES5-2.5#TRPBF LTGD 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2.5#PBF LT1761IS5-2.5#TRPBF LTGD 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-2.8#PBF LT1761ES5-2.8#TRPBF LTLB 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2.8#PBF LT1761IS5-2.8#TRPBF LTLB 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-3#PBF LT1761ES5-3#TRPBF LTGE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-3#PBF LT1761IS5-3#TRPBF LTGE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-3.3#PBF LT1761ES5-3.3#TRPBF LTGF 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-3.3#PBF LT1761IS5-3.3#TRPBF LTGF 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-3.3#PBF LT1761MPS5-3.3#TRPBF LTGF 5-Lead Plastic TSOT-23 –55°C to 125°C
LT1761-BYP LT1761-SD LT1761-X
ORDER INFORMATION
LT1761 Series
3
1761sff
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING * PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1761ES5-5#PBF LT1761ES5-5#TRPBF LTGG 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-5#PBF LT1761IS5-5#TRPBF LTGG 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-5#PBF LT1761MPS5-5#TRPBF LTGG 5-Lead Plastic TSOT-23 –55°C to 125°C
LEAD BASED FINISH TAPE AND REEL PART MARKING * PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1761ES5-BYP LT1761ES5-BYP#TR LTGC 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-BYP LT1761IS5-BYP#TR LTGC 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-SD LT1761ES5-SD#TR LTGH 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-SD LT1761IS5-SD#TR LTGH 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.2 LT1761ES5-1.2#TR LTCDS 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.2 LT1761IS5-1.2#TR LTCDS 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.5 LT1761ES5-1.5#TR LTMT 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.5 LT1761IS5-1.5#TR LTMT 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-1.8 LT1761ES5-1.8#TR LTJM 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-1.8 LT1761IS5-1.8#TR LTJM 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-1.8 LT1761MPS5-1.8#TR LTDCH 5-Lead Plastic TSOT-23 –55°C to 125°C
LT1761ES5-2 LT1761ES5-2#TR LTJE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2 LT1761IS5-2#TR LTJE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-2.5 LT1761ES5-2.5#TR LTGD 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2.5 LT1761IS5-2.5#TR LTGD 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-2.8 LT1761ES5-2.8#TR LTLB 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-2.8 LT1761IS5-2.8#TR LTLB 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-3 LT1761ES5-3#TR LTGE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-3 LT1761IS5-3#TR LTGE 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761ES5-3.3 LT1761ES5-3.3#TR LTGF 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-3.3 LT1761IS5-3.3#TR LTGF 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-3.3 LT1761MPS5-3.3#TR LTGF 5-Lead Plastic TSOT-23 –55°C to 125°C
LT1761ES5-5 LT1761ES5-5#TR LTGG 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761IS5-5 LT1761IS5-5#TR LTGG 5-Lead Plastic TSOT-23 –40°C to 125°C
LT1761MPS5-5 LT1761MPS5-5#TR LTGG 5-Lead Plastic TSOT-23 –55°C to 125°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
LT1761 Series
4
1761sff
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage (Notes 3, 11) ILOAD = 100mA l1.8 2.3 V
Regulated Output Voltage (Note 4)
LT1761-1.2 VIN = 2V, ILOAD = 1mA
2.3V < VIN < 20V, 1mA < ILOAD < 50mA
2.3V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
1.185
1.170
1.150
1.2
1.2
1.2
1.215
1.230
1.240
V
V
V
LT1761-1.5 VIN = 2V, ILOAD = 1mA
2.5V < VIN < 20V, 1mA < ILOAD < 50mA
2.5V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
1.478
1.457
1.436
1.5
1.5
1.5
1.522
1.538
1.555
V
V
V
LT1761-1.8 VIN = 2.3V, ILOAD = 1mA
2.8V < VIN < 20V, 1mA < ILOAD < 50mA
2.8V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
1.775
1.750
1.725
1.8
1.8
1.8
1.825
1.845
1.860
V
V
V
LT1761-2 VIN = 2.5V, ILOAD = 1mA
3V < VIN < 20V, 1mA < ILOAD < 50mA
3V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
1.970
1.945
1.920
2
2
2
2.030
2.045
2.060
V
V
V
LT1761-2.5 VIN = 3V, ILOAD = 1mA
3.5V < VIN < 20V, 1mA < ILOAD < 50mA
3.5V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
2.465
2.435
2.415
2.5
2.5
2.5
2.535
2.565
2.575
V
V
V
LT1761-2.8 VIN = 3.3V, ILOAD = 1mA
3.8V < VIN < 20V, 1mA < ILOAD < 50mA
3.8V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
2.762
2.732
2.706
2.8
2.8
2.8
2.838
2.868
2.884
V
V
V
LT1761-3 VIN = 3.5V, ILOAD = 1mA
4V < VIN < 20V, 1mA < ILOAD < 50mA
4V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
2.960
2.930
2.900
3
3
3
3.040
3.070
3.090
V
V
V
LT1761-3.3 VIN = 3.8V, ILOAD = 1mA
4.3V < VIN < 20V, 1mA < ILOAD < 50mA
4.3V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
3.250
3.230
3.190
3.3
3.3
3.3
3.350
3.370
3.400
V
V
V
LT1761-5 VIN = 5.5V, ILOAD = 1mA
6V < VIN < 20V, 1mA < ILOAD < 50mA
6V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
4.935
4.900
4.850
5
5
5
5.065
5.100
5.120
V
V
V
ADJ Pin Voltage (Note 3, 4) LT1761 VIN = 2V, ILOAD = 1mA
2.3V < VIN < 20V, 1mA < ILOAD < 50mA
2.3V < VIN < 20V, 1mA < ILOAD < 100mA
l
l
1.205
1.190
1.170
1.220
1.220
1.220
1.235
1.250
1.260
V
V
V
Line Regulation LT1761-1.2
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
LT1761 (Note 3)
ΔVIN = 2V to 20V, ILOAD = 1mA
ΔVIN = 2V to 20V, ILOAD = 1mA
ΔVIN = 2.3V to 20V, ILOAD = 1mA
ΔVIN = 2.5V to 20V, ILOAD = 1mA
ΔVIN = 3V to 20V, ILOAD = 1mA
ΔVIN = 3.3V to 20V, ILOAD = 1mA
ΔVIN = 3.5V to 20V, ILOAD = 1mA
ΔVIN = 3.8V to 20V, ILOAD = 1mA
ΔVIN = 5.5V to 20V, ILOAD = 1mA
ΔVIN = 2V to 20V, ILOAD = 1mA
l
l
l
l
l
l
l
l
l
l
1
1
1
1
1
1
1
1
1
1
10
10
10
10
10
10
10
10
10
10
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
LT1761 Series
5
1761sff
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Load Regulation
LT1761-1.2 VIN = 2.3V, ΔILOAD = 1mA to 50mA
VIN = 2.3V, ΔILOAD = 1mA to 50mA
VIN = 2.3V, ΔILOAD = 1mA to 100mA
VIN = 2.3V, ΔILOAD = 1mA to 100mA
l
l
1
1
6
12
12
50
mV
mV
mV
mV
LT1761-1.5 VIN = 2.5V, ΔILOAD = 1mA to 50mA
VIN = 2.5V, ΔILOAD = 1mA to 50mA
VIN = 2.5V, ΔILOAD = 1mA to 100mA
VIN = 2.5V, ΔILOAD = 1mA to 100mA
l
l
10
14
20
35
30
55
mV
mV
mV
mV
LT1761-1.8 VIN = 2.8V, ΔILOAD = 1mA to 50mA
VIN = 2.8V, ΔILOAD = 1mA to 50mA
VIN = 2.8V, ΔILOAD = 1mA to 100mA
VIN = 2.8V, ΔILOAD = 1mA to 100mA
l
l
10
15
20
35
30
60
mV
mV
mV
mV
LT1761-2 VIN = 3V, ΔILOAD = 1mA to 50mA
VIN = 3V, ΔILOAD = 1mA to 50mA
VIN = 3V, ΔILOAD = 1mA to 100mA
VIN = 3V, ΔILOAD = 1mA to 100mA
l
l
10
15
20
35
35
65
mV
mV
mV
mV
LT1761-2.5 VIN = 3.5V, ΔILOAD = 1mA to 50mA
VIN = 3.5V, ΔILOAD = 1mA to 50mA
VIN = 3.5V, ΔILOAD = 1mA to 100mA
VIN = 3.5V, ΔILOAD = 1mA to 100mA
l
l
10
20
20
35
40
80
mV
mV
mV
mV
LT1761-2.8 VIN = 3.8V, ΔILOAD = 1mA to 50mA
VIN = 3.8V, ΔILOAD = 1mA to 50mA
VIN = 3.8V, ΔILOAD = 1mA to 100mA
VIN = 3.8V, ΔILOAD = 1mA to 100mA
l
l
10
20
20
38
40
86
mV
mV
mV
mV
LT1761-3 VIN = 4V, ΔILOAD = 1mA to 50mA
VIN = 4V, ΔILOAD = 1mA to 50mA
VIN = 4V, ΔILOAD = 1mA to 100mA
VIN = 4V, ΔILOAD = 1mA to 100mA
l
l
10
20
20
40
40
90
mV
mV
mV
mV
LT1761-3.3 VIN = 4.3V, ΔILOAD = 1mA to 50mA
VIN = 4.3V, ΔILOAD = 1mA to 50mA
VIN = 4.3V, ΔILOAD = 1mA to 100mA
VIN = 4.3V, ΔILOAD = 1mA to 100mA
l
l
10
20
20
40
40
100
mV
mV
mV
mV
LT1761-5 VIN = 6V, ΔILOAD = 1mA to 50mA
VIN = 6V, ΔILOAD = 1mA to 50mA
VIN = 6V, ΔILOAD = 1mA to 100mA
VIN = 6V, ΔILOAD = 1mA to 100mA
l
l
15
25
30
60
65
150
mV
mV
mV
mV
LT1761 (Note 3) VIN = 2.3V, ΔILOAD = 1mA to 50mA
VIN = 2.3V, ΔILOAD = 1mA to 50mA
VIN = 2.3V, ΔILOAD = 1mA to 100mA
VIN = 2.3V, ΔILOAD = 1mA to 100mA
l
l
1
1
6
12
12
50
mV
mV
mV
mV
Dropout Voltage
VIN = VOUT(NOMINAL)
(Notes 5, 6, 11)
ILOAD = 1mA
ILOAD = 1mA l
0.10 0.15
0.19
V
V
ILOAD = 10mA
ILOAD = 10mA l
0.17 0.22
0.29
V
V
ILOAD = 50mA
ILOAD = 50mA l
0.24 0.28
0.38
V
V
ILOAD = 100mA
ILOAD = 100mA
0.30 0.35
0.45
V
V
LT1761 Series
6
1761sff
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
GND Pin Current
VIN = VOUT(NOMINAL)
(Notes 5, 7)
ILOAD = 0mA
ILOAD = 1mA
ILOAD = 10mA
ILOAD = 50mA
ILOAD = 100mA
l
l
l
l
l
20
55
230
1
2.2
45
100
400
2
4
μA
μA
μA
mA
mA
Output Voltage Noise COUT = 10μF, CBYP = 0.01μF, ILOAD = 100mA, BW = 10Hz to 100kHz 20 μVRMS
ADJ Pin Bias Current (Notes 3, 8) 30 100 nA
Shutdown Threshold VOUT = Off to On
VOUT = On to Off
l
l0.25
0.8
0.65
2V
V
SHDN Pin Current
(Note 9)
VSHDN = 0V
VSHDN = 20V
l
l
0
1
0.5
3
μA
μA
Quiescent Current in Shutdown VIN = 6V, VSHDN = 0V 0.01 0.1 μA
Ripple Rejection (Note 3) VIN – VOUT = 1.5V (Avg), VRIPPLE = 0.5VP-P
, fRIPPLE = 120Hz,
ILOAD = 50mA
55 65 dB
Current Limit VIN = 7V, VOUT = 0V
VIN = VOUT(NOMINAL) + 1V or 2.3V (Note 12), ΔVOUT = –5% l110
200 mA
mA
Input Reverse Leakage Current VIN = –20V, VOUT = 0V l1mA
Reverse Output Current
(Note 10)
LT1761-1.2
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
LT1761 (Note 3)
VOUT = 1.2V, VIN < 1.2V
VOUT = 1.5V, VIN < 1.5V
VOUT = 1.8V, VIN < 1.8V
VOUT = 2V, VIN < 2V
VOUT = 2.5V, VIN < 2.5V
VOUT = 2.8V, VIN < 2.8V
VOUT = 3V, VIN < 3V
VOUT = 3.3V, VIN < 3.3V
VOUT = 5V, VIN < 5V
VOUT = 1.22V, VIN < 1.22V
10
10
10
10
10
10
10
10
10
5
20
20
20
20
20
20
20
20
20
10
μA
μA
μA
μA
μA
μA
μA
μA
μA
μA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT1761 regulators are tested and specifi ed under pulse load
conditions such that TJ ≈ TA. The LT1761E is 100% production tested
at TA = 25°C. Performance at –40°C and 125°C is assured by design,
characterization and correlation with statistical process controls. The
LT1761I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT1761MP is 100% tested and guaranteed over
the –55°C to 125°C operating junction temperature range.
Note 3: The LT1761 (adjustable versions) are tested and specifi ed for
these conditions with the ADJ pin connected to the OUT pin.
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output voltage specifi cation will not apply
for all possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
Note 5: To satisfy requirements for minimum input voltage, the LT1761
(adjustable version) is tested and specifi ed for these conditions with an
external resistor divider (two 250k resistors) for an output voltage of
2.44V. The external resistor divider will add a 5μA DC load on the output.
Note 6: Dropout voltage is the minimum input to output voltage differential
needed to maintain regulation at a specifi ed output current. In dropout, the
output voltage will be equal to: VIN – VDROPOUT
.
Note 7: GND pin current is tested with VIN = VOUT(NOMINAL) or VIN = 2.3V
(whichever is greater) and a current source load. This means the device
is tested while operating in its dropout region or at the minimum input
voltage specifi cation. This is the worst-case GND pin current. The GND pin
current will decrease slightly at higher input voltages.
Note 8: ADJ pin bias current fl ows into the ADJ pin.
Note 9: SHDN pin current fl ows into the SHDN pin.
Note 10: Reverse output current is tested with the IN pin grounded and the
OUT pin forced to the rated output voltage. This current fl ows into the OUT
pin and out the GND pin.
Note 11: For the LT1761, LT1761-1.2, LT1761-1.5, LT1761-1.8 and
LT1761-2 dropout voltage will be limited by the minimum input voltage
specifi cation under some output voltage/load conditions. See the curve of
Minimum Input Voltage in the Typical Performance Characteristics.
Note 12: To satisfy requirements for minimum input voltage, current limit
is tested at VIN = VOUT(NOMINAL) + 1V or VIN = 2.3V, whichever is greater.
LT1761 Series
7
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
LT1761-1.2
Output Voltage
LT1761-1.5
Output Voltage
LT1761-1.8
Output Voltage
LT1761-2
Output Voltage
LT1761-2.5
Output Voltage
Typical Dropout Voltage Guaranteed Dropout Voltage Dropout Voltage
OUTPUT CURRENT (mA)
500
450
400
350
300
250
200
150
100
50
0
DROPOUT VOLTAGE (mV)
1761 G00
0 10203040 50 60 70 80 90 100
TJ = 125°C
TJ = 25°C
OUTPUT CURRENT (mA)
500
450
400
350
300
250
200
150
100
50
0
DROPOUT VOLTAGE (mV)
1761 G01
0 10203040 50 60 70 80 90 100
TJ ≤ 125°C
TJ ≤ 25°C
= TEST POINTS
TEMPERATURE (°C)
–50
DROPOUT VOLTAGE (mV)
050 75
1761 G01.1
–25 25 100 125
IL = 100mA
IL = 50mA
IL = 10mA
IL = 1mA
500
450
400
350
300
250
200
150
100
50
0
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (μA)
100
1761 G03
050
40
35
30
25
20
15
10
5
0–25 25 75 125
VIN = 6V
RL = ∞ (250k FOR LT1761-BYP, -SD)
IL = 0 (5μA FOR LT1761-BYP, -SD)
VSHDN = VIN
VSHDN = 0V
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G05
050
1.220
1.215
1.210
1.205
1.200
1.195
1.190
1.185
1.180 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G51
050
1.528
1.521
1.514
1.507
1.500
1.493
1.486
1.479
1.472 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G06
050
1.84
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G07
050
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G08
050
2.54
2.53
2.52
2.51
2.50
2.49
2.48
2.47
2.46 –25 25 75 125
IL = 1mA
LT1761 Series
8
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
LT1761-5
Output Voltage
LT1761-BYP, LT1761-SD
ADJ Pin Voltage
LT1761-1.2
Quiescent Current
LT1761-1.5
Quiescent Current
LT1761-1.8
Quiescent Current
LT1761-2
Quiescent Current
LT1761-2.8
Output Voltage
LT1761-3
Output Voltage
LT1761-3.3
Output Voltage
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G52
050
2.84
2.83
2.82
2.81
2.80
2.79
2.78
2.77
2.76 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G09
050
3.060
3.045
3.030
3.015
3.000
2.985
2.970
2.955
2.940 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G11
050
3.360
3.345
3.330
3.315
3.300
3.285
3.270
3.255
3.240 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G12
050
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92 –25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
ADJ PIN VOLTAGE (V)
100
1761 G10
050
1.240
1.235
1.230
1.225
1.220
1.215
1.210
1.205
1.200 –25 25 75 125
IL = 1mA
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
250
225
200
175
150
125
100
75
50
25
08
1761 G10b
213579
4610
TJ = 25°C
RL = ∞
VSHDN = 0V
VSHDN = VIN
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G53
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G18
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G19
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
LT1761 Series
9
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
LT1761-3.3
Quiescent Current
LT1761-5
Quiescent Current
LT1761-BYP, LT1761-SD
Quiescent Current
LT1761-1.2
GND Pin Current
LT1761-1.5
GND Pin Current
LT1761-1.8
GND Pin Current
LT1761-2.5
Quiescent Current
LT1761-2.8
Quiescent Current
LT1761-3
Quiescent Current
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G13
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G54
213579
4610
TJ = 25°C
RL = ∞
VSHDN = 0V
VSHDN = VIN
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G14
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G15
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (μA)
200
175
150
125
100
75
50
25
08
1761 G16
213579
4610
VSHDN = VIN
TJ = 25°C
RL = ∞
VSHDN = 0V
INPUT VOLTAGE (V)
02 6 10 14 18
QUIESCENT CURRENT (μA)
30
25
20
15
10
5
04 8 12 16
1761 G17
20
TJ = 25°C
RL = 250k
IL = 5μA
VSHDN = VIN
VSHDN = 0V
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G17b
012345678910
TJ = 25°C
*FOR VOUT = 1.2V
RL = 12Ω
IL = 100mA*
RL = 24Ω
IL = 50mA*
RL = 120Ω
IL = 10mA*
RL = 1.2k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G55
012345678910
TJ = 25°C
*FOR VOUT = 1.5V
RL = 15Ω
IL = 100mA*
RL = 30Ω
IL = 50mA*
RL = 150Ω
IL = 10mA*
RL = 1.5k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G02
012345678910
TJ = 25°C
*FOR VOUT = 1.8V
RL = 18Ω
IL = 100mA*
RL = 36Ω
IL = 50mA*
RL = 180Ω
IL = 10mA*
RL = 1.8k
IL = 1mA*
LT1761 Series
10
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
LT1761-3
GND Pin Current
LT1761-3.3
GND Pin Current
LT1761-5
GND Pin Current
LT1761-BYP, LT1761-SD
GND Pin Current GND Pin Current vs ILOAD
SHDN Pin Threshold
(On to Off)
LT1761-2
GND Pin Current
LT1761-2.5
GND Pin Current
LT1761-2.8
GND Pin Current
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G04
012345678910
TJ = 25°C
*FOR VOUT = 2V
RL = 2
IL = 100mA*
RL = 40Ω
IL = 50mA*
RL = 200Ω
IL = 10mA*
RL = 2k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G20
012345678910
TJ = 25°C
*FOR VOUT = 2.5V
RL = 25Ω
IL = 100mA
RL = 50Ω
IL = 50mA*
RL = 250Ω
IL = 10mA*
RL = 2.5k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G56
012345678910
TJ = 25°C
*FOR VOUT = 2.8V
RL = 28Ω
IL = 100mA
RL = 56Ω
IL = 50mA*
RL = 280Ω
IL = 10mA*
RL = 2.8k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G21
012345678910
TJ = 25°C
*FOR VOUT = 3V
RL = 30Ω
IL = 100mA*
RL = 60Ω
IL = 50mA*
RL = 300Ω
IL = 10mA*
RL = 3k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G22
012345678910
TJ = 25°C
*FOR VOUT = 3.3V
RL = 33Ω
IL = 100mA*
RL = 66Ω
IL = 50mA*
RL = 330Ω
IL = 10mA*
RL = 3.3k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G23
012345678910
TJ = 25°C
*FOR VOUT = 5V
RL = 50Ω
IL = 100mA
RL = 100Ω
IL = 50mA*
RL = 500Ω
IL = 10mA*
RL = 5k
IL = 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G24
012345678910
TJ = 25°C
*FOR VOUT = 1.22V
RL = 12.2Ω
IL = 100mA*
RL = 24.4Ω
IL = 50mA*
RL = 122Ω
IL = 10mA*
RL = 1.22k
IL = 1mA*
OUTPUT CURRENT (mA)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G25
0 10203040 50 60 70 80 90 100
VIN = VOUT(NOMINAL) + 1V
TEMPERATURE (°C)
–50
SHDN PIN THRESHOLD (V)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0050 75
1761 G26
–25 25 100 125
IL = 1mA
LT1761 Series
11
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
ADJ Pin Bias Current Current Limit Current Limit
Reverse Output Current Reverse Output Current Input Ripple Rejection
SHDN Pin Threshold
(Off to On) SHDN Pin Input Current SHDN Pin Input Current
TEMPERATURE (°C)
–50
SHDN PIN THRESHOLD (V)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0050 75
1761 G27
–25 25 100 125
IL = 100mA
IL = 1mA
SHDN PIN VOLTAGE (V)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
SHDN PIN INPUT CURRENT (μA)
1761 G28
012345678910
TEMPERATURE (°C)
–50
SHDN PIN INPUT CURRENT (μA)
050 75
1761 G29
–25 25 100 125
VSHDN = 20V
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
TEMPERATURE (oC)
–50
ADJ PIN BIAS CURRENT (nA)
100
90
80
70
60
50
40
30
20
10
0050 75
1761 G30
–25 25 100 125
INPUT VOLTAGE (V)
0
SHORT-CIRCUIT CURRENT (mA)
245
1761 G31
1367
350
300
250
200
150
100
50
0
VOUT = 0V
TJ = 25°C
TEMPERATURE (°C)
–50
CURRENT LIMIT (mA)
050 75
1761 G32
–25 25 100 125
350
300
250
200
150
100
50
0
VIN = 7V
VOUT = 0V
OUTPUT VOLTAGE (V)
100
90
80
70
60
50
40
30
20
10
0
REVERSE OUTPUT CURRENT (μA)
1761 G33
012345678910
TJ = 25°C
VIN = 0V
CURRENT FLOWS
INTO OUTPUT PIN
VOUT = VADJ
(LT1761-BYP, -SD)
LT1761-BYP
LT1761-SD
LT1761-2
LT1761-3.3
LT1761-5
LT1761-1.8
LT1761-1.5
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-1.2
TEMPERATURE (°C)
–50
REVERSE OUTPUT CURRENT (μA)
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0050 75
1761 G34
–25 25 100 125
VIN = 0V
VOUT = 1.22V (LT1761-BYP, -SD)
VOUT = 1.2V (LT1761-1.2)
VOUT = 1.5V (LT1761-1.5)
VOUT = 1.8V (LT1761-1.8)
VOUT = 2V (LT1761-2)
VOUT = 2.5V (LT1761-2.5)
VOUT = 2.8V (LT1761-2.8)
VOUT = 3V (LT1761-3)
VOUT = 3.3V (LT1761-3.3)
VOUT = 5V (LT1761-5)
LT1761-BYP,-SD
LT1761-1.2,-1.5,-1.8,-2,
-2.5,-2.8,-3,-3.3,-5
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
80
70
60
50
40
30
20
10
010 1k 10k 1M
1761 G35
100 100k
IL = 100mA
VIN = VOUT(NOMINAL) +
1V + 50mVRMS RIPPLE
CBYP = 0
COUT = 1μF
COUT = 10μF
LT1761-BYP
LT1761-5
LT1761 Series
12
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
Load Regulation
ΔIL = 1mA to 50mA
Load Regulation
ΔIL = 1mA to 100mA
Output Noise Spectral Density Output Noise Spectral Density
RMS Output Noise vs
Bypass Capacitor
LT1761-5
Input Ripple Rejection Input Ripple Rejection
LT1761-BYP, LT1761-SD
Minimum Input Voltage
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
80
70
60
50
40
30
20
10
010 1k 10k 1M
1761 G36
100 100k
IL = 100mA
VIN = VOUT(NOMINAL) +
1V + 50mVRMS RIPPLE
COUT = 10μF
CBYP = 0.01μF
CBYP = 100pF
CBYP = 1000pF
TEMPERATURE (°C)
–50
RIPPLE REJECTION (dB)
100
1761 G37
050
80
70
60
50
40
30
20
10
0–25 25 75 125
VIN = VOUT (NOMINAL) +
1V + 0.5VP-P RIPPLE
AT f = 120Hz
IL = 50mA
TEMPERATURE (°C)
–50
MINIMUM INPUT VOLTAGE (V)
2.5
2.0
1.5
1.0
0.5
0050 75
1761 G38
–25 25 100 125
IL = 100mA
IL = 50mA
TEMPERATURE (°C)
–50
LOAD REGULATION (mV)
100
1761 G39
050
0
–5
–10
–15
–20
–25
–30
–35
–40 –25 25 75 125
LT1761-BYP, -SD, -1.2
LT1761-1.8
LT1761-1.5
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
TEMPERATURE (°C)
–50
LOAD REGULATION (mV)
100
1761 G40
050
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100 –25 25 75 125
LT1761-3
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-5
LT1761-3.3
LT1761-BYP, -SD, -1.2
LT1761-1.8
LT1761-1.5
FREQUENCY (Hz)
10 1k 10k 100k
1761 G41
100
10
1
0.1
0.01
OUTPUT NOISE SPECTRAL DENSITY (μV/√Hz)
COUT = 10μF
CBYP = 0
IL = 100mA
LT1761-BYP,
-SD, 1.2
LT1761-5
LT1761-3.3
LT1761-2.8,-3
LT1761-2.5
LT1761-1.8
LT1761-2
LT1761-1.5
FREQUENCY (Hz)
10 1k 10k 100k
1761 G42
100
10
1
0.1
0.01
OUTPUT NOISE SPECTRAL DENSITY (μV/√Hz)
LT1761-BYP
LT1761-5 CBYP = 1000pF
CBYP = 0.01μF
CBYP = 100pF
COUT = 10μF
IL = 100mA
CBYP (pF)
10
OUTPUT NOISE (μVRMS)
140
120
100
80
60
40
20
0100 1k 10k
1761 G43
COUT = 10μF
IL = 100mA
f = 10Hz TO 100kHz
LT1761-5
LT1761-3.3
LT1761-3
LT1761-2.8
LT1761-2.5
LT1761-1.5
LT1761-1.8, -2
LT1761-BYP, -1.2
LT1761 Series
13
1761sff
TYPICAL PERFORMANCE CHARACTERISTICS
RMS Output Noise vs
Load Current (10Hz to 100kHz)
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 0pF
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 100pF
LOAD CURRENT (mA)
0.01
OUTPUT NOISE (μVRMS)
160
140
120
100
80
60
40
20
00.1 1
1761 G44
10 100
COUT = 10μF
LT1761-5
LT1761-5
LT1761-BYP
LT1761-BYP
CBYP = 0
CBYP = 0.01μF
VOUT
100μV/DIV
1ms/DIVCOUT = 10μF
IL = 100mA
1761 G45
VOUT
100μV/DIV
1ms/DIVCOUT = 10μF
IL = 100mA
1761 G46
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 1000pF
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 0.01μF
VOUT
100μV/DIV
1ms/DIVCOUT = 10μF
IL = 100mA
1761 G46
VOUT
100μV/DIV
1ms/DIVCOUT = 10μF
IL = 100mA
1761 G48
LT1761-5 Transient Response
CBYP = 0pF
LT1761-5 Transient Response
CBYP = 0.01μF
TIME (μs)
0.2
0.1
0
–0.1
–0.2
OUTPUT VOLTAGE
DEVIATION (V)
100
50
0
LOAD CURRENT
(mA)
1761 G49
0 400 800 1200 1600 2000
VIN = 6V
CIN = 10μF
COUT = 10μF
TIME (μs)
0.04
0.02
0
–0.02
–0.04
OUTPUT VOLTAGE
DEVIATION (V)
100
50
0
LOAD CURRENT
(mA)
1761 G50
0 40 60 10020 80 120 140 180160 200
VIN = 6V
CIN = 10μF
COUT = 10μF
LT1761 Series
14
1761sff
PIN FUNCTIONS
IN (Pin 1): Input. Power is supplied to the device through
the IN pin. A bypass capacitor is required on this pin if
the device is more than six inches away from the main
input fi lter capacitor. In general, the output impedance
of a battery rises with frequency, so it is advisable to
include a bypass capacitor in battery-powered circuits. A
bypass capacitor in the range of 1μF to 10μF is suffi cient.
The LT1761 regulators are designed to withstand reverse
voltages on the IN pin with respect to ground and the OUT
pin. In the case of a reverse input, which can happen if
a battery is plugged in backwards, the device will act as
if there is a diode in series with its input. There will be
no reverse current fl ow into the regulator and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
GND (Pin 2): Ground.
SHDN (Pin 3, Fixed/-SD Devices): Shutdown. The SHDN
pin is used to put the LT1761 regulators into a low power
shutdown state. The output will be off when the SHDN pin
is pulled low. The SHDN pin can be driven either by 5V logic
or open-collector logic with a pull-up resistor. The pull-up
resistor is required to supply the pull-up current of the
open-collector gate, normally several microamperes, and
the SHDN pin current, typically 1μA. If unused, the SHDN
pin must be connected to VIN. The device will not function
if the SHDN pin is not connected. For the LT1761-BYP, the
SHDN pin is internally connected to VIN.
BYP (Pins 3/4, Fixed/-BYP Devices): Bypass. The BYP
pin is used to bypass the reference of the LT1761 regula-
tors to achieve low noise performance from the regulator.
The BYP pin is clamped internally to ±0.6V (one VBE) from
ground. A small capacitor from the output to this pin will
bypass the reference to lower the output voltage noise.
A maximum value of 0.01μF can be used for reducing
output voltage noise to a typical 20μVRMS over a 10Hz
to 100kHz bandwidth. If not used, this pin must be left
unconnected.
ADJ (Pin 4, Adjustable Devices Only): Adjust Pin. For the
adjustable LT1761, this is the input to the error amplifi er.
This pin is internally clamped to ±7V. It has a bias current
of 30nA which fl ows into the pin (see curve of ADJ Pin
Bias Current vs Temperature in the Typical Performance
Characteristics section). The ADJ pin voltage is 1.22V
referenced to ground and the output voltage range is
1.22V to 20V.
OUT (Pin 5): Output. The output supplies power to the load.
A minimum output capacitor of 1μF is required to prevent
oscillations. Larger output capacitors will be required for
applications with large transient loads to limit peak volt-
age transients. See the Applications Information section
for more information on output capacitance and reverse
output characteristics.
LT1761 Series
15
1761sff
APPLICATIONS INFORMATION
The LT1761 series are 100mA low dropout regulators with
micropower quiescent current and shutdown. The devices
are capable of supplying 100mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20μVRMS
over a 10Hz to 100kHz bandwidth with the addition of a
0.01μF reference bypass capacitor. Additionally, the refer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (20μA)
drops to less than 1μA in shutdown. In addition to the
low quiescent current, the LT1761 regulators incorporate
several protection features which make them ideal for use
in battery-powered systems. The devices are protected
against both reverse input and reverse output voltages.
In battery backup applications where the output can be
held up by a backup battery when the input is pulled to
ground, the LT1761-X acts like it has a diode in series with
its output and prevents reverse current fl ow. Additionally,
in dual supply applications where the regulator load is
returned to a negative supply, the output can be pulled
below ground by as much as 20V and still allow the device
to start and operate.
Adjustable Operation
The adjustable version of the LT1761 has an output voltage
range of 1.22V to 20V. The output voltage is set by the
ratio of two external resistors as shown in Figure 1. The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
equal to 1.22V/R1 and the current in R2 is the current in
R1 plus the ADJ pin bias current. The ADJ pin bias cur-
rent, 30nA at 25°C, fl ows through R2 into the ADJ pin.
The output voltage can be calculated using the formula in
Figure 1. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the
ADJ pin bias current. Note that in shutdown the output is
turned off and the divider current will be zero. Curves of
ADJ Pin Voltage vs Temperature and ADJ Pin Bias Cur-
rent vs Temperature appear in the Typical Performance
Characteristics.
The adjustable device is tested and specifi ed with the ADJ
pin tied to the OUT pin for an output voltage of 1.22V.
Specifi cations for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage
to 1.22V: VOUT/1.22V. For example, load regulation for an
output current change of 1mA to 100mA is –1mV typical
at VOUT = 1.22V. At VOUT = 12V, load regulation is:
(12V/1.22V)(–1mV) = –9.8mV
Bypass Capacitance and Low Noise Performance
The LT1761 regulators may be used with the addition of a
bypass capacitor from OUT to the BYP pin to lower output
voltage noise. A good quality low leakage capacitor is rec-
ommended. This capacitor will bypass the reference of the
regulator, providing a low frequency noise pole. The noise
pole provided by this bypass capacitor will lower the output
voltage noise to as low as 20μVRMS with the addition of a
0.01μF bypass capacitor. Using a bypass capacitor has the
added benefi t of improving transient response. With no
bypass capacitor and a 10μF output capacitor, a 10mA to
100mA load step will settle to within 1% of its fi nal value
in less than 100μs. With the addition of a 0.01μF bypass
capacitor, the output will stay within 1% for a 10mA to
100mA load step (see LT1761-5 Transient Response in
Typical Performance Characteristics section). However,
regulator start-up time is proportional to the size of the
bypass capacitor, slowing to 15ms with a 0.01μF bypass
capacitor and 10μF output capacitor.
IN
1761 F01
R2
LT1761
OUT
VIN
VOUT
ADJ
GND
R1
+VV
R
RIR
VV
InA
OUT ADJ
ADJ
ADJ

¥
§
¦´
µ

o
122 1 2
12
122
30
AT 25 C
OUTPUT RANGE = 1.22V TO 20V
Figure 1. Adjustable Operation
LT1761 Series
16
1761sff
APPLICATIONS INFORMATION
Output Capacitance and Transient Response
The LT1761 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capaci-
tors. A minimum output capacitor of 1μF with an ESR of
3Ω or less is recommended to prevent oscillations. The
LT1761-X is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
and provide improved transient response for larger load
current changes. Bypass capacitors, used to decouple
individual components powered by the LT1761-X, will
increase the effective output capacitor value. With larger
capacitors used to bypass the reference (for low noise
operation), larger values of output capacitors are needed.
For 100pF of bypass capacitance, 2.2μF of output capaci-
tor is recommended. With a 330pF bypass capacitor or
larger, a 3.3μF output capacitor is recommended. The
shaded region of Figure 2 defi nes the region over which
the LT1761 regulators are stable. The minimum ESR
needed is defi ned by the amount of bypass capacitance
used, while the maximum ESR is 3Ω.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
dielectrics used are specifi ed with EIA temperature char-
acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but they tend to have strong voltage
OUTPUT CAPACITANCE (μF)
1
ESR (Ω)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0310
1761 F02
245
678
9
STABLE REGION
CBYP = 330pF
CBYP = 100pF
CBYP = 0
CBYP > 3300pF
Figure 2. Stability
and temperature coeffi cients as shown in Figures 3 and 4.
When used with a 5V regulator, a 16V 10μF Y5V capacitor
can exhibit an effective value as low as 1μF to 2μF for the
DC bias voltage applied and over the operating tempera-
ture range. The X5R and X7R dielectrics result in more
stable characteristics and are more suitable for use as the
output capacitor. The X7R type has better stability across
temperature, while the X5R is less expensive and is avail-
able in higher values. Care still must be exercised when
using X5R and X7R capacitors; the X5R and X7R codes
only specify operating temperature range and maximum
capacitance change over temperature. Capacitance change
due to DC bias with X5R and X7R capacitors is better than
Y5V and Z5U capacitors, but can still be signifi cant enough
to drop capacitor values below appropriate levels. Capaci-
tor DC bias characteristics tend to improve as component
case size increases, but expected capacitance at operating
voltage should be verifi ed.
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
1761 F03
20
0
–20
–40
–60
–80
–100 04810
26 12 14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
Figure 3. Ceramic Capacitor DC Bias Characteristics
Figure 4. Ceramic Capacitor Temperature Characteristics
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100 25 75
1761 F04
–25 0 50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
LT1761 Series
17
1761sff
APPLICATIONS INFORMATION
Voltage and temperature coeffi cients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. A ceramic capacitor produced
Figure 5’s trace in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
VOUT
500μV/DIV
LT1761-5
COUT = 10μF
CBYP = 0.01μF
ILOAD = 100mA
100ms/DIV 1761 F05
Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be made up of two
components:
1. Output current multiplied by the input/output voltage
differential: (IOUT)(VIN – VOUT), and
2. GND pin current multiplied by the input voltage:
(IGND)(VIN).
The ground pin current can be found by examining the
GND Pin Current curves in the Typical Performance Char-
acteristics section. Power dissipation will be equal to the
sum of the two components listed above.
The LT1761 series regulators have internal thermal limiting
designed to protect the device during overload conditions.
For continuous normal conditions, the maximum junction
temperature rating of 125°C must not be exceeded. It is
important to give careful consideration to all sources of
thermal resistance from junction to ambient. Additional
heat sources mounted nearby must also be considered.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with one ounce
copper.
Table 1. Measured Thermal Resistance
COPPER AREA
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE
2500mm22500mm22500mm2125°C/W
1000mm22500mm22500mm2125°C/W
225mm22500mm22500mm2130°C/W
100mm22500mm22500mm2135°C/W
50mm22500mm22500mm2150°C/W
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
range of 4V to 6V, an output current range of 0mA to 50mA
LT1761 Series
18
1761sff
and a maximum ambient temperature of 50°C, what will
the maximum junction temperature be?
The power dissipated by the device will be equal to:
I
OUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX))
where,
I
OUT(MAX) = 50mA
V
IN(MAX) = 6V
I
GND at (IOUT = 50mA, VIN = 6V) = 1mA
So,
P = 50mA(6V – 3.3V) + 1mA(6V) = 0.14W
The thermal resistance will be in the range of 125°C/W to
150°C/W depending on the copper area. So the junction
temperature rise above ambient will be approximately
equal to:
0.14W(150°C/W) = 21.2°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T
JMAX = 50°C + 21.2°C = 71.2°C
Protection Features
The LT1761 regulators incorporate several protection
features which make them ideal for use in battery-pow-
ered circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
limiting and thermal limiting, the devices are protected
against reverse input voltages, reverse output voltages
and reverse voltages from output to input.
APPLICATIONS INFORMATION
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation,
the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages
of 20V. Current fl ow into the device will be limited to less
than 1mA (typically less than 100μA) and no negative
voltage will appear at the output. The device will protect
both itself and the load. This provides protection against
batteries which can be plugged in backward.
The output of the LT1761-X can be pulled below ground
without damaging the device. If the input is left open circuit
or grounded, the output can be pulled below ground by
20V. For fi xed voltage versions, the output will act like a
large resistor, typically 500k or higher, limiting current fl ow
to typically less than 100μA. For adjustable versions, the
output will act like an open circuit; no current will fl ow out
of the pin. If the input is powered by a voltage source, the
output will source the short-circuit current of the device
and will protect itself by thermal limiting. In this case,
grounding the SHDN pin will turn off the device and stop
the output from sourcing the short-circuit current.
The ADJ pin of the adjustable device can be pulled above
or below ground by as much as 7V without damaging the
device. If the input is left open circuit or grounded, the
ADJ pin will act like an open circuit when pulled below
ground and like a large resistor (typically 100k) in series
with a diode when pulled above ground.
LT1761 Series
19
1761sff
OUTPUT VOLTAGE (V)
100
90
80
70
60
50
40
30
20
10
0
REVERSE OUTPUT CURRENT (μA)
1761 F06
012345678910
TJ = 25°C
VIN = 0V
CURRENT FLOWS
INTO OUTPUT PIN
VOUT = VADJ
(LT1761-BYP, -SD)
LT1761-BYP
LT1761-SD
LT1761-2
LT1761-3.3
LT1761-5
LT1761-1.8
LT1761-1.5
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-1.2
Figure 6. Reverse Output Current
APPLICATIONS INFORMATION
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp volt-
age if the output is pulled high, the ADJ pin input current
must be limited to less than 5mA. For example, a resistor
divider is used to provide a regulated 1.5V output from the
1.22V reference when the output is forced to 20V. The top
resistor of the resistor divider must be chosen to limit the
current into the ADJ pin to less than 5mA when the ADJ
pin is at 7V. The 13V difference between output and ADJ
pin divided by the 5mA maximum current into the ADJ pin
yields a minimum top resistor value of 2.6k.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled
to ground, pulled to some intermediate voltage or is left
open circuit. Current fl ow back into the output will follow
the curve shown in Figure 6.
When the IN pin of the LT1761-X is forced below the OUT
pin or the OUT pin is pulled above the IN pin, input cur-
rent will typically drop to less than 2μA. This can happen
if the input of the device is connected to a discharged
(low voltage) battery and the output is held up by either
a backup battery or a second regulator circuit. The state
of the SHDN pin will have no effect on the reverse output
current when the output is pulled above the input.
LT1761 Series
20
1761sff
PACKAGE DESCRIPTION
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
DATUM ‘A
0.09 – 0.20
(NOTE 3) S5 TSOT-23 0302 REV B
PIN ONE
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
LT1761 Series
21
1761sff
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
F 5/10 Added MP-grade
Added Typical Application
2, 3
22
(Revision history begins at Rev F)
LT1761 Series
22
1761sff
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
LT 0510 REV F • PRINTED IN USA
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Operation, Monolithic, 100% Duty Cycle
TYPICAL APPLICATION
OUT
BYP
IN
SHDN
LT1761-5
1μF
VIN
5.4V TO 20V
OFF ON
CBYP 10μF
1761 TA02a
5V
AT 100mA
GND
CBYP (pF)
10
0.1
STARTUP TIME (ms)
1
10
100
100 1000 10000
1761 TA02b
Startup Time
Noise Bypassing Provides Soft-Start

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