LT1761IS5-BYP#PBF - LINEAR TECHNOLOGY

LT1761 Series

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

SHDN

0.01μF 10μF

1761 TA01

OUT

VIN

5.4V TO

20V BYP

GND

LT1761-5

5V AT100mA

20μVRMS NOISE

1μF +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

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

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

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

1.185

1.170

1.150

1.2

1.215

1.230

1.240

LT1761-1.5 VIN = 2V, ILOAD = 1mA

2.5V < VIN < 20V, 1mA < ILOAD < 50mA

2.5V < VIN < 20V, 1mA < ILOAD < 100mA

1.478

1.457

1.436

1.5

1.522

1.538

1.555

LT1761-1.8 VIN = 2.3V, ILOAD = 1mA

2.8V < VIN < 20V, 1mA < ILOAD < 50mA

2.8V < VIN < 20V, 1mA < ILOAD < 100mA

1.775

1.750

1.725

1.8

1.825

1.845

1.860

LT1761-2 VIN = 2.5V, ILOAD = 1mA

3V < VIN < 20V, 1mA < ILOAD < 50mA

3V < VIN < 20V, 1mA < ILOAD < 100mA

1.970

1.945

1.920

2.030

2.045

2.060

LT1761-2.5 VIN = 3V, ILOAD = 1mA

3.5V < VIN < 20V, 1mA < ILOAD < 50mA

3.5V < VIN < 20V, 1mA < ILOAD < 100mA

2.465

2.435

2.415

2.5

2.535

2.565

2.575

LT1761-2.8 VIN = 3.3V, ILOAD = 1mA

3.8V < VIN < 20V, 1mA < ILOAD < 50mA

3.8V < VIN < 20V, 1mA < ILOAD < 100mA

2.762

2.732

2.706

2.8

2.838

2.868

2.884

LT1761-3 VIN = 3.5V, ILOAD = 1mA

4V < VIN < 20V, 1mA < ILOAD < 50mA

4V < VIN < 20V, 1mA < ILOAD < 100mA

2.960

2.930

2.900

3.040

3.070

3.090

LT1761-3.3 VIN = 3.8V, ILOAD = 1mA

4.3V < VIN < 20V, 1mA < ILOAD < 50mA

4.3V < VIN < 20V, 1mA < ILOAD < 100mA

3.250

3.230

3.190

3.3

3.350

3.370

3.400

LT1761-5 VIN = 5.5V, ILOAD = 1mA

6V < VIN < 20V, 1mA < ILOAD < 50mA

6V < VIN < 20V, 1mA < ILOAD < 100mA

4.935

4.900

4.850

5.065

5.100

5.120

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

1.205

1.190

1.170

1.220

1.235

1.250

1.260

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 = 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

LT1761 Series

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

LT1761-1.5 VIN = 2.5V, ΔILOAD = 1mA to 50mA

VIN = 2.5V, ΔILOAD = 1mA to 50mA

VIN = 2.5V, ΔILOAD = 1mA to 100mA

LT1761-1.8 VIN = 2.8V, ΔILOAD = 1mA to 50mA

VIN = 2.8V, ΔILOAD = 1mA to 50mA

VIN = 2.8V, ΔILOAD = 1mA to 100mA

LT1761-2 VIN = 3V, ΔILOAD = 1mA to 50mA

VIN = 3V, ΔILOAD = 1mA to 50mA

VIN = 3V, ΔILOAD = 1mA to 100mA

LT1761-2.5 VIN = 3.5V, ΔILOAD = 1mA to 50mA

VIN = 3.5V, ΔILOAD = 1mA to 50mA

VIN = 3.5V, ΔILOAD = 1mA to 100mA

LT1761-2.8 VIN = 3.8V, ΔILOAD = 1mA to 50mA

VIN = 3.8V, ΔILOAD = 1mA to 50mA

VIN = 3.8V, ΔILOAD = 1mA to 100mA

LT1761-3 VIN = 4V, ΔILOAD = 1mA to 50mA

VIN = 4V, ΔILOAD = 1mA to 50mA

VIN = 4V, ΔILOAD = 1mA to 100mA

LT1761-3.3 VIN = 4.3V, ΔILOAD = 1mA to 50mA

VIN = 4.3V, ΔILOAD = 1mA to 50mA

VIN = 4.3V, ΔILOAD = 1mA to 100mA

100

LT1761-5 VIN = 6V, ΔILOAD = 1mA to 50mA

VIN = 6V, ΔILOAD = 1mA to 50mA

VIN = 6V, ΔILOAD = 1mA to 100mA

150

LT1761 (Note 3) VIN = 2.3V, ΔILOAD = 1mA to 50mA

VIN = 2.3V, ΔILOAD = 1mA to 50mA

VIN = 2.3V, ΔILOAD = 1mA to 100mA

Dropout Voltage

VIN = VOUT(NOMINAL)

(Notes 5, 6, 11)

ILOAD = 1mA

ILOAD = 1mA l

0.10 0.15

0.19

ILOAD = 10mA

ILOAD = 10mA l

0.17 0.22

0.29

ILOAD = 50mA

ILOAD = 50mA l

0.24 0.28

0.38

ILOAD = 100mA

0.30 0.35

0.45

LT1761 Series

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

230

2.2

100

400

μA

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

l0.25

0.8

0.65

SHDN Pin Current

(Note 9)

VSHDN = 0V

VSHDN = 20V

0.5

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

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

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

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

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

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

TEMPERATURE (°C)

–50

QUIESCENT CURRENT (μA)

100

1761 G03

050

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

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)

QUIESCENT CURRENT (μA)

250

225

200

175

150

125

100

1761 G10b

213579

4610

TJ = 25°C

RL = ∞

VSHDN = 0V

VSHDN = VIN

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G53

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G18

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G19

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

LT1761 Series

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)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G13

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G54

213579

4610

TJ = 25°C

RL = ∞

VSHDN = 0V

VSHDN = VIN

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G14

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G15

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

QUIESCENT CURRENT (μA)

200

175

150

125

100

1761 G16

213579

4610

VSHDN = VIN

TJ = 25°C

RL = ∞

VSHDN = 0V

INPUT VOLTAGE (V)

02 6 10 14 18

QUIESCENT CURRENT (μA)

04 8 12 16

1761 G17

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

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

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

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

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

GND PIN CURRENT (mA)

1761 G04

012345678910

TJ = 25°C

*FOR VOUT = 2V

RL = 20Ω

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

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

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

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

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

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

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

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

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

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

TEMPERATURE (oC)

–50

ADJ PIN BIAS CURRENT (nA)

100

0050 75

1761 G30

–25 25 100 125

INPUT VOLTAGE (V)

SHORT-CIRCUIT CURRENT (mA)

245

1761 G31

1367

350

300

250

200

150

100

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

VIN = 7V

VOUT = 0V

OUTPUT VOLTAGE (V)

100

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)

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

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)

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

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

–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

–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

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

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)

OUTPUT NOISE (μVRMS)

140

120

100

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

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

00.1 1

1761 G44

10 100

COUT = 10μF

LT1761-5

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

–0.1

–0.2

OUTPUT VOLTAGE

DEVIATION (V)

100

LOAD CURRENT

(mA)

1761 G49

0 400 800 1200 1600 2000

VIN = 6V

CIN = 10μF

COUT = 10μF

TIME (μs)

0.04

0.02

–0.02

–0.04

OUTPUT VOLTAGE

DEVIATION (V)

100

LOAD CURRENT

(mA)

1761 G50

0 40 60 10020 80 120 140 180160 200

VIN = 6V

CIN = 10μF

COUT = 10μF

LT1761 Series

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

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.

1761 F01

LT1761

OUT

VIN

VOUT

ADJ

GND

+VV

RIR

InA

OUT ADJ

ADJ



¦´

µ





o

122 1 2

122



AT 25 C

OUTPUT RANGE = 1.22V TO 20V

Figure 1. Adjustable Operation

LT1761 Series

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)

ESR (Ω)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0310

1761 F02

245

678

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

–40

–60

–80

–100 04810

26 12 14

X5R

Y5V

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

Figure 3. Ceramic Capacitor DC Bias Characteristics

Figure 4. Ceramic Capacitor Temperature Characteristics

TEMPERATURE (°C)

–50

–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

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

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:

OUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX))

where,

OUT(MAX) = 50mA

IN(MAX) = 6V

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:

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

1761sff

OUTPUT VOLTAGE (V)

100

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

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

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

(Revision history begins at Rev F)

LT1761 Series

1761sff

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0510 REV F • PRINTED IN USA

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TYPICAL APPLICATION

OUT

BYP

SHDN

LT1761-5

1μF

VIN

5.4V TO 20V

OFF ON

CBYP 10μF

1761 TA02a

AT 100mA

GND

CBYP (pF)

0.1

STARTUP TIME (ms)

100

100 1000 10000

1761 TA02b

Startup Time

Noise Bypassing Provides Soft-Start