Linear Technology LT3695 Series User manual

LT3695 Series
1
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
I
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
VC
0.22µF
VOUT
5V
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
RT
PG
40.2k
16.2k SYNC
BOOSTON OFF
SW
DA
FB
GND PGND
LOAD CURRENT (A)
0
50
EFFICIENCY (%)
60
70
80
90
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
2
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VIN, RUN/SS Voltage (Note 3)...................................60V
BOOST Pin Voltage ...................................................50V
BOOST Pin Above SW Pin.........................................30V
BD Voltage (LT3695).................................................30V
RT
, 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
1
2
3
4
5
6
7
8
PGND
DA
NC
SW
RUN/SS
RT
SYNC
VIN
16
15
14
13
12
11
10
9
BOOST
BD
GND
PG
NC
FB
NC
VC
TOP VIEW
17
PGND
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W WITH EXPOSED PAD SOLDERED
θJA = 110°C/W WITHOUT EXPOSED PAD SOLDERED
1
2
3
4
5
6
7
8
PGND
DA
NC
SW
RUN/SS
RT
SYNC
VIN
16
15
14
13
12
11
10
9
BOOST
NC
OUT1
OUT2
GND
PG
NC
VC
TOP VIEW
MSE PACKAGE
16-LEAD PLASTIC MSOP
17
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
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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
l
l
3.4
3.4
3.6
4.3
V
V
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
l
0.01
35
90
0.5
60
160
µA
µA
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
55
0
0.5
100
–5
µA
µA
µA
Quiescent Current from OUT1,2 Pins
LT3695-3.3 VRUN/SS = 0.2V
VRUN/SS = 10V, VOUT1,2 = 3.3V, Not Switching l
5
43
10
65
15
112
µA
µA
LT3695-5 VRUN/SS = 0.2V
VRUN/SS = 10V, VOUT1,2 = 5V, Not Switching l
5
43
10
65
15
112
µA
µA
Minimum BD Pin Voltage: LT3695 2.8 3 V
Feedback Voltage: LT3695
l
792
785
800
800
808
815
mV
mV
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
l
3.27
3.25
3.3
3.3
3.33
3.35
V
V
LT3695-5
l
4.95
4.925
5
5
5.05
5.075
V
V
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
MHz
kHz
Minimum Switch Off-Time E- and I-Grades
H-Grade
l
l
130
130
210
250
ns
ns
Switch Current Limit (Note 7) SYNC = 0V
SYNC = 3.3V or Clocked
1.45
1.18
1.7
1.4
2
1.66
A
A

LT3695 Series
4
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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
12
7.5
20
µA
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
5
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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 (%)
60
70
40
50
80
1000
3695 G01
30
10
20
110 100
90
VIN = 12V
VIN = 34V
L = 10µH
f = 800kHz
VIN = 24V
LOAD CURRENT (mA)
EFFICIENCY (%)
3695 G02
0.1
60
70
40
50
80
1000
30
10
20
110 100
90
VIN = 12V
VIN = 34V
L = 10µH
f = 800kHz
VIN = 24V
LOAD CURRENT (mA)
0.1
EFFICIENCY (%)
POWER LOSS(W)
70
60
80
90
1000
3695 G03
20
30
40
50
10 110 100
100
0.1
0.01
0.001
1
VIN = 12V
VOUT = 3.3V
L = 10µH
f = 800kHz
No-Load Supply Current
INPUT VOLTAGE (V)
05
LOAD CURRENT (A)
1.25
1.00
0.75
1.50
40
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)
5
LOAD CURRENT (A)
1.00
0.75
1.25
40
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)
8
LOAD CURRENT (A)
1.00
1.25
20
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)
0
LOAD CURRENT (A)
1.50
1.25
1.75
40
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)
05
SUPPLY CURRENT (µA)
140
120
60
80
100
40
20
010 2015 30
3695 G04
4025 35
VOUT = 3.3V

LT3695 Series
6
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BOOST Pin Current Feedback Voltage
Switching Frequency Frequency Foldback: LT3695
Switch Current Limit
Switch Current Limit
(SYNC Pin Grounded) Switch Voltage Drop
TYPICAL PERFORMANCE CHARACTERISTICS
TA= 25°C, unless otherwise noted.
DUTY CYCLE (%)
0
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)
0
VOLTAGE DROP (mV)
300
1.25
3695 G12
100
200
00.25 0.50 0.75 1.00
400
SWITCH CURRENT (A)
0
BOOST PIN CURRENT (mA)
20
25
15
10
30
1.25
3695 G13
5
00.25 0.50 0.75 1.00
35
FB PIN VOLTAGE (mV)
0
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)
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
0
200
400
600
800
1000
1200
OUTPUT VOLTAGE (V)
RRT = 29.4k

LT3695 Series
7
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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)
0
RUN/SS PIN CURRENT (µA)
10
8
35 40
3695 G22
4
2
6
0510 15 20 3025
12
FB PIN ERROR VOLTAGE (mV)
–200
VCPIN CURRENT (µA)
0
10
20
30
–10
40
50
200
3659 G24
–40
–30
–50
–20
–60 –100 0 100
60
LOAD CURRENT (mA)
1
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)
0
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)
0
BOOST DIODE VF(V)
1.0
0.8
1.2
1
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
80
60
40
0
20
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
5
0
200
400
600
800
1000
1200
OUTPUT VOLTAGE (V)
RRT = 29.4k
0
10
20
30
–10
40
50
–40
–30
–50
–20
–60
60
VCPIN CURRENT (µA)
–750 –500 –250 0 250
3695 G25
500 750
OUTPUT ERROR VOLTAGE (mV)
0
10
20
30
–10
40
50
–40
–30
–50
–20
–60
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
8
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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
0
30
35
1
20
25
15
10
50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6
40
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
IL
0.2A/DIV
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 5mA
3695 G34 1µs/DIV
VSW
5V/DIV
VOUT
20mV/DIV
IL
0.2A/DIV
3695 G35
VIN = 12V, FRONT PAGE APPLICATION
ILOAD = 55mA
1µs/DIV
VSW
5V/DIV
VOUT
20mV/DIV
IL
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)
0
VIN (V)
30
35
1
3695 G29
20
25
15
10
50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6
40
TA= 85˚C
VOUT = 3.3V
L = 10µH
f = 800kHz
SYNC = 3.3V
TA= 25˚C
LOAD CURRENT(A)
VIN (V)
3695 G30
0
30
35
1
20
25
15
10
50.1 0.2 0.3 0.4 0.5 0.7 0.90.80.6
40
TA= 85˚C
VOUT = 5V
L = 10µH
f = 800kHz
SYNC = 5V
TA= 25˚C
LOAD CURRENT (mA)
1
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
9
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
10
3695fa
BLOCK DIAGRAM
VIN
VIN
VOUT
C1
RT
PG
RUN/SS
SYNC
RT
+
–
INTERNAL 0.8V REF
11
+
–
SOFT-START
0.720V
ERROR AMP
OSCILLATOR
250kHz TO 2.2MHz
DISABLE
SYNC
OUT
OUTB
+
–
+
–
Burst Mode
DETECT
THERMAL
SHUTDOWN
VCCLAMP
2
4
15
16
9
5
7
13
8
6
R1R2
FBGND
OVLO
SLOPE COMP
R
SQ
DA
PGND
SW
BOOST
BD
VC
CC
C3
L1
D1 C2
CF
RC
3695 BDa
1
PGND
17
14
VIN
VIN
VOUT
C1
RT
PG
RUN/SS
SYNC
RT
+
–
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
2
4
14
16
9
5
7
11
8
6
R1R2
GND
OVLO
SLOPE COMP
R
SQ
DA
PGND
SW
BOOST
OUT1
13
OUT2
VC
CC
C3
L1
D1 C2
CF
RC
3695 BD
1
PGND
17
12
LT3695-3.3/LT3695-5
LT3695