Linear Technology LT3695 Series User manual

LT3695 Series

3695fa

TYPICAL APPLICATION

DESCRIPTION

1A Fault Tolerant Micropower

Step-Down Regulator

The LT

3695 series are adjustable frequency (250kHz to

2.2MHz) monolithic buck switching regulators that accept

input voltages up to 36V and can safely sustain transient

voltages up to 60V. The devices include a high efﬁciency

switch, a boost diode, and the necessary oscillator, control

and logic circuitry. Current mode topology is used for fast

transient response and good loop stability. A SYNC pin

allowstheusertosynchronizetheparttoanexternalclock,

and to choose between low ripple Burst Mode operation

and standard PWM operation.

The LT3695 regulators tolerate adjacent pin shorts or

an open pin without raising the output voltage above its

programmed value.

Low ripple Burst Mode operation maintains high efﬁ-

ciency at low output currents while keeping output ripple

below 15mV in a typical application. Shutdown reduces

input supply current to less than 1µA while a resistor and

capacitor on the RUN/SS pin provide a controlled output

voltage ramp (soft-start). Protection circuitry senses the

current in the power switch and external Schottky catch

diodetoprotecttheLT3695regulatorsagainst short-circuit

conditions. Frequency foldback and thermal shutdown

provide additional protection.

The LT3695 series is available in a thermally enhanced

16-pin MSOP package.

5V Step-Down Converter

FEATURES

APPLICATIONS

nWide Input Range:

Operation from 3.6V to 36V

Overvoltage Lockout Protects Circuits Through

60V Transients

nFMEA Fault Tolerant:

Output Stays at or Below Regulation Voltage

During Adjacent Pin Short or When a Pin Is Left

Floating

n1A Output Current

nLow Ripple (< 15mVP-P) Burst Mode

Operation

Q= 75μA for 12VIN to 3.3VOUT with No Load

nAdjustable Switching Frequency: 250kHz to 2.2MHz

nShort-Circuit Protected

nSynchronizable Between 300kHz and 2.2MHz

nOutput Voltage: 0.8V to 20V

nPower Good Flag

nFixed Output Voltage Versions for 3.3V and 5V Available

nSmall, Thermally Enhanced 16-Pin MSOP Package

nAutomotive Battery Regulation

nAutomotive Entertainment Systems

nDistributed Supply Regulation

nIndustrial Supplies

Efﬁciency

VIN BD

LT3695

RUN/SS

0.22µF

VOUT

0.9A, VIN > 6.9V

1A, VIN > 12V

102k

f = 800kHz

536k

10µH

10µF

3695 TA01a

470pF

2.2µF

VIN

6.9V TO 36V

TRANSIENT TO 60V

40.2k

16.2k SYNC

BOOSTON OFF

GND PGND

LOAD CURRENT (A)

EFFICIENCY (%)

100

0.2 0.4 0.6 0.8 1

VOUT = 5V

VOUT = 3.3V

VIN = 12V

L = 10μH

f = 800kHz

3695 TA01b

L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of

Linear Technology Corporation. All other trademarks are the property of their respective owners.

LT3695 Series

3695fa

VIN, RUN/SS Voltage (Note 3)...................................60V

BOOST Pin Voltage ...................................................50V

BOOST Pin Above SW Pin.........................................30V

BD Voltage (LT3695).................................................30V

, VCVoltage ............................................................5V

RT Pin Current .........................................................1mA

SYNC Voltage............................................................20V

FB Voltage (LT3695)....................................................5V

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3695EMSE#PBF LT3695EMSE#TRPBF 3695 16-Lead Plastic MSOP –40°C to 125°C

LT3695IMSE#PBF LT3695IMSE#TRPBF 3695 16-Lead Plastic MSOP –40°C to 125°C

LT3695HMSE#PBF LT3695HMSE#TRPBF 3695 16-Lead Plastic MSOP –40°C to 150°C

LT3695EMSE-3.3#PBF LT3695EMSE-3.3#TRPBF 369533 16-Lead Plastic MSOP –40°C to 125°C

LT3695IMSE-3.3#PBF LT3695IMSE-3.3#TRPBF 369533 16-Lead Plastic MSOP –40°C to 125°C

LT3695HMSE-3.3#PBF LT3695HMSE-3.3#TRPBF 369533 16-Lead Plastic MSOP –40°C to 150°C

LT3695EMSE-5#PBF LT3695EMSE-5#TRPBF 36955 16-Lead Plastic MSOP –40°C to 125°C

LT3695IMSE-5#PBF LT3695IMSE-5#TRPBF 36955 16-Lead Plastic MSOP –40°C to 125°C

LT3695HMSE-5#PBF LT3695HMSE-5#TRPBF 36955 16-Lead Plastic MSOP –40°C to 150°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based ﬁnish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

ABSOLUTE MAXIMUM RATINGS

(Notes 1, 2)

LT3695 LT3695-3.3, LT3695-5

PGND

RUN/SS

SYNC

VIN

BOOST

GND

TOP VIEW

PGND

MSE PACKAGE

16-LEAD PLASTIC MSOP

θJA = 40°C/W WITH EXPOSED PAD SOLDERED

θJA = 110°C/W WITHOUT EXPOSED PAD SOLDERED

PGND

RUN/SS

SYNC

VIN

BOOST

OUT1

OUT2

GND

TOP VIEW

MSE PACKAGE

16-LEAD PLASTIC MSOP

PGND

θJA = 40°C/W WITH EXPOSED PAD SOLDERED

θJA = 110°C/W WITHOUT EXPOSED PAD SOLDERED

PIN CONFIGURATION

OUT1, OUT2 Voltage (LT3695-3.3, LT3695-5)...........16V

PG Voltage ................................................................30V

Operating Junction Temperature Range (Notes 4, 5)

LT3695E............................................. –40°C to 125°C

LT3695I.............................................. –40°C to 125°C

LT3695H ............................................ –40°C to 150°C

Storage Temperature Range................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) .................. 300°C

LT3695 Series

3695fa

ELECTRICAL CHARACTERISTICS

The ldenotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA= 25°C. VIN = 10V, VRUN/SS = 10V, unless otherwise noted. (Note 4)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Operating Voltage (Note 6)

LT3695 VBD = 3.3V

VBD < 3V

3.4

3.6

4.3

LT3695-3.3 VOUT1,2 = 3.3V l3.4 3.6 V

LT3695-5 VOUT1,2 = 5V l3.4 3.6 V

VIN Overvoltage Lockout l36 38 39.9 V

Quiescent Current from VIN

LT3695

VRUN/SS = 0.2V VBD = 3.3V

VRUN/SS = 10V, VBD = 3.3V, Not Switching

VRUN/SS = 10V, VBD = 0V, Not Switching

0.01

0.5

160

µA

LT3695-3.3 VRUN/SS = 10V, VOUT1,2 = 3.3V, Not Switching l35 60 µA

LT3695-5 VRUN/SS = 10V, VOUT1,2 = 5V, Not Switching l35 60 µA

Quiescent Current from BD Pin

LT3695 VRUN/SS = 0.2V, VBD = 3.3V

VRUN/SS = 10V, VBD = 3.3V, Not Switching

VRUN/SS = 10V, VBD = 0V, Not Switching

l35

0.01

0.5

100

–5

µA

Quiescent Current from OUT1,2 Pins

LT3695-3.3 VRUN/SS = 0.2V

VRUN/SS = 10V, VOUT1,2 = 3.3V, Not Switching l

112

µA

LT3695-5 VRUN/SS = 0.2V

VRUN/SS = 10V, VOUT1,2 = 5V, Not Switching l

112

µA

Minimum BD Pin Voltage: LT3695 2.8 3 V

Feedback Voltage: LT3695

792

785

800

808

815

FB Pin Bias Current: LT3695 FB Pin Voltage = 800mV l–5 –40 nA

Reference Voltage Line Regulation 3.6V < VIN < 36V 0.001 0.005 %/V

Output Voltage

LT3695-3.3

3.27

3.25

3.3

3.33

3.35

LT3695-5

4.95

4.925

5.05

5.075

Error Amp gmIVC = ±1.5µA 430 µS

Error Amp Voltage Gain 1300 V/V

VCSource Current 50 µA

VCSink Current 50 µA

VCPin to Switch Current Gain 1.25 A/V

VCSwitching Threshold 0.4 0.6 0.8 V

VCClamp Voltage 2V

Switching Frequency RRT = 8.06k

RRT = 29.4k

RRT = 158k

1.98

0.9

225

2.2

1.0

250

2.42

1.1

275

MHz

kHz

Minimum Switch Off-Time E- and I-Grades

H-Grade

130

210

250

Switch Current Limit (Note 7) SYNC = 0V

SYNC = 3.3V or Clocked

1.45

1.18

1.7

1.4

1.66

LT3695 Series

3695fa

ELECTRICAL CHARACTERISTICS

The ldenotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA= 25°C. VIN = 10V, VRUN/SS = 10V, unless otherwise noted. (Note 4)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Switch VCESAT ISW = 1A 350 mV

DA Pin Current to Stop OSC 1.25 1.6 1.95 A

Switch Leakage Current VSW = 0V, VIN = 36V 0.01 1 µA

Boost Schottky Diode Voltage Drop IBSD = 50mA 720 900 mV

Boost Schottky Diode Reverse Leakage VSW = 10V, VBD = 0V 0.1 1 µA

Minimum Boost Voltage (Note 8) l1.7 2.3 V

BOOST Pin Current ISW = 0.5A 10.5 17.5 mA

RUN/SS Pin Current VRUN/SS = 2.5V

VRUN/SS = 10V

l4.5

7.5

µA

RUN/SS Input Voltage High 2.5 V

RUN/SS Input Voltage Low 0.2 V

PG Leakage Current VPG = 5V 0.1 1 µA

PG Sink Current VPG = 0.4V l100 1000 µA

PG Threshold as % of VFB (LT3695) or

VOUT (LT3695-3.3, LT3695-5)

Measured at FB (LT3695) or OUT1,2 (LT3695-3.3, LT3695-5)

Pins (Pin Voltage Rising)

88 90 92 %

PG Threshold Hysteresis

LT3695 Measured at FB Pin 12 mV

LT3695-3.3 Measured at OUT1,2, Pins 50 mV

LT3695-5 Measured at OUT1,2, Pins 75 mV

SYNC Threshold Voltage 300 550 800 mV

SYNC Input Frequency 0.3 2.2 MHz

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 the device

reliability and lifetime.

Note 2: Positive currents ﬂow into pins, negative currents ﬂow out of pins.

Minimum and maximum values refer to absolute values.

Note 3: Absolute maximum voltage at VIN and RUN/SS pins is 60V for

nonrepetitive 1 second transients, and 36V for continuous operation.

Note 4: The LT3695E regulators are guaranteed to meet performance

speciﬁcations from 0°C to 125°C junction temperature. Speciﬁcations

over the –40°C to 125°C operating junction temperature range are

assured by design, characterization and correlation with statistical process

controls. The LT3695I regulators are guaranteed over the full –40°C to

125°C operating junction temperature range. The LT3695H regulators are

guaranteed over the full –40°C to 150°C operating junction temperature

range.

Note 5: These ICs include overtemperature protection that is intended

to protect the devices during momentary overload conditions. Junction

temperature will exceed the maximum operating junction temperature

when overtemperature protection is active. Continuous operation above

the speciﬁed maximum operating junction temperature may impair device

reliability.

Note 6: This is the voltage necessary to keep the internal bias circuitry in

regulation.

Note 7: Current limit guaranteed by design and/or correlation to static test.

Slope compensation reduces current limit at higher duty cycles.

Note 8: This is the minimum voltage across the boost capacitor needed to

guarantee full saturation of the switch.

LT3695 Series

3695fa

TYPICAL PERFORMANCE CHARACTERISTICS

No-Load Supply Current Maximum Load Current

Maximum Load Current Maximum Load Current Maximum Load Current

Efﬁciency (VOUT = 5V, SYNC = 0V)

TA= 25°C, unless otherwise noted.

Efﬁciency (VOUT = 3.3V, SYNC = 0V) Efﬁciency (VOUT = 3.3V, SYNC = 0V)

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

1000

3695 G01

110 100

VIN = 12V

VIN = 34V

L = 10µH

f = 800kHz

VIN = 24V

LOAD CURRENT (mA)

EFFICIENCY (%)

3695 G02

0.1

1000

110 100

VIN = 12V

VIN = 34V

L = 10µH

f = 800kHz

VIN = 24V

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS(W)

1000

3695 G03

10 110 100

100

0.1

0.01

0.001

VIN = 12V

VOUT = 3.3V

L = 10µH

f = 800kHz

No-Load Supply Current

INPUT VOLTAGE (V)

LOAD CURRENT (A)

1.25

1.00

0.75

1.50

3695 G06

0.50

0.25 10 15 20 30 3525

1.75

TYPICAL

MINIMUM

VOUT = 3.3V

L = 10µH

f = 800kHz

SYNC = 0V

SYNC = 3.3V

INPUT VOLTAGE (V)

LOAD CURRENT (A)

1.00

0.75

1.25

3682 G07

0.50

0.25 10 15 20 30 3525

1.50

TYPICAL

MINIMUM

VOUT = 5V

L = 10µH

f = 800kHz

SYNC = 0V

SYNC = 5V

INPUT VOLTAGE (V)

LOAD CURRENT (A)

1.00

1.25

3695 G08

0.50

0.75

0.25 10 12 14 16 18

1.50

TYPICAL

MINIMUM

VOUT = 5V

L = 4.7µH

f = 2MHz

SYNC = 0V

SYNC = 5V

INPUT VOLTAGE (V)

LOAD CURRENT (A)

1.50

1.25

1.75

3695 G09

1.00

0.75

0.50

0.25 510 15 20 30 3525

TYPICAL

MINIMUM

VOUT = 1.8V

L = 10µH

f = 500kHz

SYNC = 0V

SYNC = 3.3V

TEMPERATURE (°C)

–50

SUPPLY CURRENT (µA)

1300

1200

500

600

700

800

900

1000

1100

400

200

300

100

0050–25 25 100

3695 G05

15075 125

CATCH DIODE: DIODES, INC. B140

VIN = 12V

VOUT = 3.3V

INCREASED SUPPLY CURRENT

DUE TO CATCH DIODE LEAKAGE

AT HIGH TEMPERATURE

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

140

120

100

010 2015 30

3695 G04

4025 35

VOUT = 3.3V

LT3695 Series

3695fa

BOOST Pin Current Feedback Voltage

Switching Frequency Frequency Foldback: LT3695

Switch Current Limit

(SYNC Pin Grounded) Switch Voltage Drop

TYPICAL PERFORMANCE CHARACTERISTICS

TA= 25°C, unless otherwise noted.

DUTY CYCLE (%)

SWITCH CURRENT LIMIT (A)

1.3

1.1

1.5

1.7

100

3695 G10

0.7

0.9

0.5 20 40 60 80

1.9

SYNC < 0.3V

SYNC > 0.8V

OR CLOCKED

SWITCH CURRENT (A)

VOLTAGE DROP (mV)

300

1.25

3695 G12

100

200

00.25 0.50 0.75 1.00

400

SWITCH CURRENT (A)

BOOST PIN CURRENT (mA)

1.25

3695 G13

00.25 0.50 0.75 1.00

FB PIN VOLTAGE (mV)

FREQUENCY (kHz)

1000

900

3695 G17

800

600

400

200

0100 200 300 400 600 700 800500

1200

RRT = 29.4k

TEMPERATURE (°C)

–50

FEEDBACK VOLTAGE (mV)

810

790

800

780

770 050–25 25 100

3695 G14

15075 125

TEMPERATURE (°C)

–50

FREQUENCY (MHz)

1.20

1.15

1.10

1.05

1.00

0.80

0.85

0.90

0.95

050–25 25 100

3695 G16

15075 125

RT= 29.4k

TEMPERATURE (°C)

–50

SWITCH CURRENT LIMIT (A)

1.9

1.7

1.5

1.3

1.1

0.5

0.7

0.9

050–25 25 100

3695 G11

15075 125

DC = 10%

DC = 90%

Output Voltage:

LT3695-3.3, LT3695-5

Frequency Foldback: LT3695-3.3

TEMPERATURE (°C)

–50

OUTPUT VOLTAGE (V)

3.35

3.25

3.15

3.30

3.20

3.10

5.15

5.05

4.95

5.10

5.00

4.90

050–25 25 100

3695 G15

15075 125

LT3695-3.3

LT3695-5

FREQUENCY (kHz)

00.5 1.51 2 2.5

3695 G18

3 3.5

200

400

600

800

1000

1200

OUTPUT VOLTAGE (V)

RRT = 29.4k

LT3695 Series

3695fa

Minimum Switch On-Time Soft-Start

TYPICAL PERFORMANCE CHARACTERISTICS

RUN/SS Pin Current

TA= 25°C, unless otherwise noted.

Boost Diode Forward Voltage

Error Ampliﬁer Output Current:

LT3695

RUN/SS PIN VOLTAGE (V)

RUN/SS PIN CURRENT (µA)

35 40

3695 G22

0510 15 20 3025

FB PIN ERROR VOLTAGE (mV)

–200

VCPIN CURRENT (µA)

–10

200

3659 G24

–40

–30

–50

–20

–60 –100 0 100

LOAD CURRENT (mA)

INPUT VOLTAGE (V)

4.0

3.5

4.5

1000

3695 G27

2.5

3.0

2.0 10 100

5.0 VOUT = 3.3V

L = 10µH

f = 800kHz

RUN/SS PIN VOLTAGE (V)

SWITCH CURRENT LIMIT (A)

1.4

0.8

1.0

1.2

1.6

1.8

3.5

3695 G21

0.4

0.2

0.6

00.5 1.0 1.5 2.0 3.02.5

2.0 SYNC < 0.3V

BOOST DIODE CURRENT (A)

BOOST DIODE VF(V)

1.0

0.8

1.2

3695 G23

0.4

0.2

0.6

00.25 0.5 0.75

1.4

Minimum Input Voltage

TEMPERATURE (°C)

–50

MINIMUM SWITCH ON TIME (ns)

120

100

050–25 25 100

3695 G20

15075 125

IOUT = 1A

Error Ampliﬁer Output Current:

LT3695-3.3

Frequency Foldback: LT3695-5

FREQUENCY (kHz)

01324

3695 G19

200

400

600

800

1000

1200

OUTPUT VOLTAGE (V)

RRT = 29.4k

–10

–40

–30

–50

–20

–60

VCPIN CURRENT (µA)

–750 –500 –250 0 250

3695 G25

500 750

OUTPUT ERROR VOLTAGE (mV)

–10

–40

–30

–50

–20

–60

VCPIN CURRENT (µA)

–900 –600 –300 0 300

3695 G26

600 900

OUTPUT ERROR VOLTAGE (mV)

Error Ampliﬁer Output Current:

LT3695-5

LT3695 Series

3695fa

Maximum VIN for Full Frequency VCVoltages

Switching Waveforms,

60V Input Voltage Transient

Switching Waveforms,

Burst Mode Operation

Switching Waveforms,

Transition from Burst Mode

Operation to Full Frequency

TYPICAL PERFORMANCE CHARACTERISTICS

TA= 25°C, unless otherwise noted.

LOAD CURRENT(A)

VIN (V)

3695 G31

50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6

TA= 85˚C

TA= 25˚C

VOUT = 5V

L = 4.7µH

f = 2MHz

SYNC = 5V

Switching Waveforms,

Full Frequency Continuous

Operation

TEMPERATURE (°C)

–50

VCVOLTAGE (V)

2.5

1.5

0.5

2.0

1.0

0050–25 25 100

3695 G32

15075 125

CURRENT LIMIT CLAMP

SWITCHING THRESHOLD 5ms/DIV

VSW

10V/DIV

VOUT

5V/DIV

VIN

20V/DIV

VIN = 12V, FRONT PAGE APPLICATION

ILOAD = 500mA

3695 G33

5µs/DIV

VSW

5V/DIV

VOUT

20mV/DIV

0.2A/DIV

VIN = 12V, FRONT PAGE APPLICATION

ILOAD = 5mA

3695 G34 1µs/DIV

VSW

5V/DIV

VOUT

20mV/DIV

0.2A/DIV

3695 G35

VIN = 12V, FRONT PAGE APPLICATION

ILOAD = 55mA

1µs/DIV

VSW

5V/DIV

VOUT

20mV/DIV

0.5A/DIV

3695 G36

VIN = 12V, FRONT PAGE APPLICATION

ILOAD = 500mA

Maximum VIN for Full Frequency Maximum VIN for Full Frequency

LOAD CURRENT(A)

VIN (V)

3695 G29

50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6

TA= 85˚C

VOUT = 3.3V

L = 10µH

f = 800kHz

SYNC = 3.3V

TA= 25˚C

LOAD CURRENT(A)

VIN (V)

3695 G30

50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6

TA= 85˚C

VOUT = 5V

L = 10µH

f = 800kHz

SYNC = 5V

TA= 25˚C

LOAD CURRENT (mA)

INPUT VOLTAGE (V)

5.5

5.0

6.0

1000

3695 G28

4.5

410 100

6.5 VOUT = 5V

L = 10µH

f = 800kHz

Minimum Input Voltage

LT3695 Series

3695fa

PIN FUNCTIONS

PGND (Pin 1, Exposed Pad Pin 17/Pin 1, Exposed Pad

Pin 17): This is the power ground used by the catch diode

(D1 in the Block Diagram) when its anode is connected to

the DA pin. The exposed pad may be soldered to the PCB

in order to lower the thermal resistance.

DA (Pin 2/Pin 2): Connect the anode of the catch diode

(D1) to this pin. Internal circuitry senses the current

through the catch diode providing frequency foldback in

extreme situations.

NC (Pins 3, 10, 12/Pins 3, 10, 15): No Connects. These

pins are not connected to internal circuitry and must be

left ﬂoating to ensure fault tolerance.

SW (Pin 4/Pin 4): The SW pin is the output of the internal

power switch. Connect this pin to the inductor, catch diode

and boost capacitor.

RUN/SS (Pin 5/Pin 5): The RUN/SS pin is used to put

the LT3695 regulators in shutdown mode. Tie to ground

to shut down the LT3695 regulators. Tie to 2.5V or more

for normal operation. RUN/SS also provides a soft-start

function; see the Applications Information section for

more information.

RT (Pin 6/Pin 6): Oscillator Resistor Input. Connect a

resistor from this pin to ground to set the switching

frequency.

SYNC (Pin 7/Pin 7): This is the external clock synchroni-

zation input. Ground this pin with a 100k resistor for low

ripple Burst Mode operation at low output loads. Tie to

0.8V or more for pulse-skipping mode operation. Tie to a

clocksourcefor synchronization. Clock edges should have

rise and fall times faster than 1µs. Note that the maximum

load current depends on which mode is chosen. See the

Applications Information section for more information.

VIN (Pin 8/Pin 8): The VIN pin supplies current to the

internal regulator and to the internal power switch. This

pin must be locally bypassed.

VC(Pin 9/Pin 9): The VCpin is the output of the internal

error ampliﬁer. The voltage on this pin controls the peak

switch current. Tie an RC network from this pin to ground

to compensate the control loop.

FB(Pin 11)LT3695: TheLT3695 regulates theFB pinto 0.8V.

Connect the feedback resistor divider tap to this pin.

PG (Pin 13/Pin 11): ThePG pin is the open-collector output

of an internal comparator. PG remains low until the FB pin

(LT3695) or the OUT1,2 pins (LT3695-3.3, LT3695-5) are

within 10% of the ﬁnal regulation voltage. PG output is

valid when VIN is above the minimum input voltage and

RUN/SS is high.

GND (Pin 14/Pin 12): The GND pin is the ground of all the

internal circuitry. Tie directly to the local GND plane.

OUT1, OUT2, (Pins 14, 13) LT3695-3.3, LT3695-5: These

pins connect to the anode of the boost Schottky diode and

also supply current to the internal regulator. They also

connect to the internal feedback resistors and must be

connected to the output.

BD (Pin 15) LT3695: This pin connects to the anode of

the boost Schottky diode and also supplies current to the

LT3695’s internal regulator.

BOOST (Pin 16/Pin 16): This pin is used to provide a

drive voltage, higher than the input voltage, to the internal

bipolar NPN power switch. Connect a capacitor (typically

0.22µF) between BOOST and SW.

(LT3695/LT3695-3.3, LT3695-5)

LT3695 Series

3695fa

BLOCK DIAGRAM

VIN

VOUT

RUN/SS

SYNC

–

INTERNAL 0.8V REF

–

SOFT-START

0.720V

ERROR AMP

OSCILLATOR

250kHz TO 2.2MHz

DISABLE

SYNC

OUT

OUTB

–

Burst Mode

DETECT

THERMAL

SHUTDOWN

VCCLAMP

R1R2

FBGND

OVLO

SLOPE COMP

PGND

BOOST

D1 C2

3695 BDa

PGND

VIN

VOUT

RUN/SS

SYNC

–

INTERNAL 0.8V REF

–

SOFT-START

0.720V

ERROR AMP

OSCILLATOR

250kHz TO 2.2MHz

DISABLE

SYNC

OUT

OUTB

–

Burst Mode

DETECT

THERMAL

SHUTDOWN

VCCLAMP

R1R2

GND

OVLO

SLOPE COMP

PGND

BOOST

OUT1

OUT2

D1 C2

3695 BD

PGND

LT3695-3.3/LT3695-5

LT3695

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