LINEAR TECHNOLOGY LT3693 Technical data
FEATURES
LT3693
36V, 3.5A, 2.4MHz
Step-Down Switching Regulator
U
DESCRIPTIO
■
Wide Input Range: 3.6V to 36V
■
3.5A Maximum Output Current
■
Adjustable Switching Frequency: 200kHz to 2.4MHz
■
Low Shutdown Current: IQ < 1μA
■
Integrated Boost Diode
■
Synchronizable Between 250kHz to 2MHz
■
Power Good Flag
■
Saturating Switch Design: 95m On-Resistance
■
0.790V Feedback Reference Voltage
■
Output Voltage: 0.79V to 30V
■
Thermal Protection
■
Soft-Start Capability
■
Small 10-Pin Thermally Enhanced MSOP and
(3mm × 3mm) DFN Packages
U
APPLICATIO S
■
Automotive Battery Regulation
■
Power for Portable Products
■
Distributed Supply Regulation
■
Industrial Supplies
■
Wall Transformer Regulation
The LT®3693 is an adjustable frequency (200kHz to
2.4MHz) monolithic buck switching regulator that accepts
input voltages up to 36V. A high effi ciency 95m switch
is included on the die along with a boost Schottky diode
and the necessary oscillator, control, and logic circuitry.
Current mode topology is used for fast transient response
and good loop stability. 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). A power good fl ag signals when V
reaches
OUT
91% of the programmed output voltage. The LT3693 is
available in 10-Pin MSOP and 3mm × 3mm DFN packages
with exposed pads for low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
5V Step-Down Converter
V
IN
6.3V TO 36V
V
OFF ON
15k
10mF
680pF
63.4k
RUN/SS BOOST
V
C
RT
PG
SYNC
IN
U
LT3693
GND
BD
SW
Effi ciency
V
OUT
5V
3.5A
0.47mF
4.7mH
100k
536k
47mF
3693 TA01a
FB
100
90
80
70
EFFICIENCY (%)
60
V
= 5V
OUT
L = 4.7μH
f = 600kHz
50
0 0.5
VIN = 12V
1.5
VIN = 34V
2
VIN = 24V
1
OUTPUT CURRENT (A)
2.5
3
3.5
3693 G01
3693f
1
LT3693
WW
W
ABSOLUTE AXI U RATI GS
U
(Note 1)
VIN, RUN/SS Voltage .................................................36V
BOOST Pin Voltage ...................................................56V
BOOST Pin Above SW Pin .........................................30V
FB, RT, V
Voltage .......................................................5V
C
PG, BD Voltage .........................................................30V
SYNC Voltage ............................................................20V
PIN CONFIGURATION
TOP VIEW
10
BD
1
BOOST
2
11
3
SW
4
V
IN
5
RUN/SS
10-LEAD (3mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
DD PACKAGE
θJA = 45°C/W, θJC = 10°C/W
RT
9
V
C
FB
8
7
PG
6
SYNC
Operating Junction Temperature Range (Note 2)
LT3693E ............................................. –40°C to 125°C
LT3693I.............................................. –40°C to 125°C
Storage Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(MSE Only) ....................................................... 300°C
TOP VIEW
10
1
BD
2
BOOST
SW
V
IN
RUN/SS
10-LEAD PLASTIC MSOP
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
θJA = 45°C/W, θJC = 10°C/W
3
4
5
MSE PACKAGE
11
RT
9
V
C
FB
8
PG
7
SYNC
6
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3693EDD#PBF LT3693EDD#TRPBF LDGB 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3693IDD#PBF LT3693IDD#TRPBF LDGB 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3693EMSE#PBF LT3693EMSE#TRPBF LTDFZ 10-Lead Plastic MSOP –40°C to 125°C
LT3693IMSE#PBF LT3693IMSE#TRPBF LTDFZ 10-Lead Plastic MSOP –40°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.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
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/
ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
= 25°C. VIN = 10V, V
A
noted. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage
V
Quiescent Current from V
Quiescent Current from BD V
IN
= 0.2V 0.01 0.5 μA
RUN/SS
= 3V, Not Switching
V
BD
= 0, Not Switching 1.3 2.3 mA
V
BD
= 0.2V 0.01 0.5 μA
RUN/SS
= 3V, Not Switching
V
BD
RUN/SS
= 10V, V
= 15V, VBD = 3.3V unless otherwise
BOOST
●
●
●
3 3.6 V
0.45 1.2 mA
0.9 1.8 mA
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LT3693
ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
noted. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Bias Voltage (BD Pin) 2.7 3 V
Feedback Voltage
FB Pin Bias Current (Note 3) V
FB Voltage Line Regulation 4V < V
Error Amp g
Error Amp Gain 2000
Source Current 60 μA
V
C
Sink Current 60 μA
V
C
Pin to Switch Current Gain 5.3 A/V
V
C
Clamp Voltage 2.0 V
V
C
Switching Frequency R
Minimum Switch Off-Time
Switch Current Limit Duty Cycle = 5% 4.6 5.4 6.0 A
Switch V
Boost Schottky Reverse Leakage V
Minimum Boost Voltage (Note 4)
BOOST Pin Current I
RUN/SS Pin Current V
RUN/SS Input Voltage High 2.5 V
RUN/SS Input Voltage Low 0.2 V
PG Threshold Offset from Feedback Voltage VFB Rising 65 mV
PG Hysteresis 10 mV
PG Leakage V
PG Sink Current V
SYNC Low Threshold 0.5 V
SYNC High Threshold 0.8 V
SYNC Pin Bias Current V
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 LT3693E is guaranteed to meet performance specifi cations
from 0°C to 125°C. Specifi cations over the –40°C to 125°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3693I specifi cations are
guaranteed over the –40°C to 125°C temperature range.
m
CESAT
= 25°C. VIN = 10V, V
A
= 0, Not Switching 110 μA
V
BD
= 0.8V, VC = 0.4V
FB
< 36V 0.002 0.01 %/V
IN
= 8.66k
T
R
= 29.4k
T
R
= 187k
T
ISW = 3.5A 335 mV
= 10V, VBD = 0V 0.02 2 μA
SW
= 1A 35 60 mA
SW
= 2.5V 5 8 μA
RUN/SS
= 5V 0.1 1 μA
PG
= 0.4V
PG
= 0V 0.1 μA
SYNC
Note 3: Bias current fl ows out of the FB pin.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
RUN/SS
= 10V, V
= 15V, VBD = 3.3V unless otherwise
BOOST
780
775
●
●
2.2
1.0
200
●
●
●
200 800 μA
790
790
10 40 nA
525 μMho
2.45
1.1
230
60 150 nS
1.5 2.0 V
800
805
2.7
1.25
260
mV
mV
MHz
MHz
kHz
3693f
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LT3693
UW
TYPICAL PERFOR A CE CHARACTERISTICS
= 25°C unless otherwise noted.
T
A
Effi ciency
100
90
80
70
EFFICIENCY (%)
60
V
OUT
L = 4.7μH
f = 600kHz
50
0 0.5
VIN = 24V
= 5V
1
OUTPUT CURRENT (A)
Maximum Load Current
5.5
5.0
4.5
4.0
3.5
LOAD CURRENT (A)
V
T
3.0
L = 4.7μH
f = 600kHz
2.5
5
TYPICAL
MINIMUM
= 3.3V
OUT
= 25°C
A
10 20
INPUT VOLTAGE (V)
15
1.5
VIN = 12V
VIN = 34V
2
2.5
25 30
3
3693 G01
3693 G06
3.5
Effi ciency
100
90
80
70
EFFICIENCY (%)
60
V
OUT
L = 3.3μH
f = 600kHz
50
0 0.5
VIN = 12V
VIN = 24V
= 3.3V
1
OUTPUT CURRENT (A)
Maximum Load Current
5.5
5.0
4.5
4.0
LOAD CURRENT (A)
V
= 5V
OUT
3.5
= 25°C
T
A
L = 4.7μH
f = 600kHz
3.0
10 20
5
VIN = 34V
2
1.5
15
INPUT VOLTAGE (V)
2.5
TYPICAL
MINIMUM
3.5
3
3693 G02
25 30
3693 G07
Effi ciency
100
90
80
70
EFFICIENCY (%)
VIN = 12V
60
= 5V
V
OUT
L = 4.7μH
f = 600kHz
50
0 0.5
OUTPUT CURRENT (A)
Switch Current Limit
6.0
5.5
5.0
4.5
4.0
SWITCH CURRENT LIMIT(A)
3.5
3.0
0
2
1.5
1
20 60
40
DUTY CYCLE (%)
2.5
3.5
3
3693 G03
80 100
3.0
2.5
TOTAL POWER LOSS (W)
2.0
1.5
1.0
0.5
3693 G08
Switch Current Limit
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
SWITCH CURRENT LIMIT (A)
2.5
2.0
–50 25–25 0 50 75 100 150125
DUTY CYCLE = 10 %
DUTY CYCLE = 90 %
TEMPERATURE (°C)
4
3693 G09
Switch Voltage Drop
700
600
500
400
300
VOLTAGE DROP (mV)
200
100
0
0
12 45
SWITCH CURRENT (A)
Boost Pin Current
120
105
90
75
60
45
30
BOOST PIN CURRENT (mA)
15
3
3693 G10
0
0312 45
SWITCH CURRENT (A)
3693 G11
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0
TYPICAL PERFOR A CE CHARACTERISTICS
LT3693
TA = 25°C unless otherwise noted.
Feedback Voltage
840
820
800
780
FEEDBACK VOLTAGE (mV)
760
–50 25–25 0 50 75 100 150125
TEMPERATURE (°C)
Minimum Switch On-Time
140
120
100
80
60
40
MINIMUM SWITCH ON TIME (ns)
20
3693 G12
Switching Frequency
1.20
RT = 34.0k
1.15
1.10
1.05
1.00
0.95
FREQUENCY (MHz)
0.90
0.85
0.80
–50 25–25 0 50 75 100 150125
TEMPERATURE (oC)
Soft-Start
7
6
5
4
3
2
SWITCH CURRENT LIMIT (A)
1
3693 G13
Frequency Foldback
1200
RT = 34.0k
1000
800
600
400
SWITCHING FREQUENCY (kHz)
200
0
0
200 400
100 300
FB PIN VOLTAGE (mV)
RUN/SS Pin Current
12
10
8
6
4
RUN/SS PIN CURRENT (μA)
2
500
700 900
600
800
3693 G14
0
–50 25–25 0 50 75 100 150125
TEMPERATURE (°C)
Boost Diode
1.4
1.2
1.0
(V)
F
0.8
0.6
BOOST DIODE V
0.4
0.2
0
0
0.5 1.0 1.5
BOOST DIODE CURRENT (A)
3693 G15
3693 G18
2.0
0
0.5 1 2
0
1.5
RUN/SS PIN VOLTAGE (V)
Error Amp Output Current
50
40
30
20
10
0
–10
PIN CURRENT (μA)
C
–20
V
–30
–40
–50
–200
–100 100
FB PIN ERROR VOLTAGE (mV)
2.5 3 3.5
3693 G16
0 200
3693 G19
0
0
510
RUN/SS PIN VOLTAGE (V)
Minimum Input Voltage
5.0
4.5
4.0
3.5
3.0
INPUT VOLTAGE (V)
V
= 3.3V
OUT
2.5
= 25oC
T
A
L = 4.7MH
f = 600kHz
2.0
10 100 1000
1
LOAD CURRENT (mA)
20 30 35
15 25
3693 G17
1000
3693 G20
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LT3693
0
UW
TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C unless otherwise noted.
Minimum Input Voltage
6.5
6.0
5.5
5.0
INPUT VOLTAGE (V)
V
= 5V
OUT
4.5
= 25 oC
T
A
L = 4.7MH
f = 600kHz
4.0
1 1000
10 100 1000
LOAD CURRENT (mA)
Switching Waveforms;
Discontinuous Operation
V
SW
5V/DIV
I
L
0.2A/DIV
3693 G21
VC Voltages
2.50
2.00
1.50
VOLTAGE (V)
1.00
C
V
0.50
CURRENT LIMIT CLAMP
SWITCHING THRESHOLD
0
–50 25–25 0 50 75 100 150125
TEMPERATURE (°C)
3693 G22
Switching Waveforms;
Continuous Operation
V
SW
5V/DIV
I
L
0.5A/DIV
Power Good Threshold
95
90
85
80
THRESHOLD VOLTAGE (%)
75
–50 25–25 0 50 75 100 150125
TEMPERATURE (°C)
3693 G23
V
OUT
10mV/DIV
VIN = 12V
V
= 3.3V
OUT
I
= 110mA
LOAD
1μs/DIV
3693 G25
V
OUT
10mV/DIV
VIN = 12V
V
= 3.3V
OUT
I
= 1A
LOAD
1μs/DIV
3693 G26
3693f
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UUU
PI FU CTIO S
LT3693
BD (Pin 1): This pin connects to the anode of the boost
Schottky diode. BD also supplies current to the internal
regulator.
BOOST (Pin 2): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
SW (Pin 3): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
(Pin 4): The VIN pin supplies current to the LT3693’s
V
IN
internal regulator and to the internal power switch. This
pin must be locally bypassed.
RUN/SS (Pin 5): The RUN/SS pin is used to put the
LT3693 in shutdown mode. Tie to ground to shut down
the LT3693. Tie to 2.5V or more for normal operation. If
the shutdown feature is not used, tie this pin to the V
IN
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
SYNC (Pin 6): This is the external clock synchronization
input. Ground this pin when not used. Tie to a clock source
for synchronization. Clock edges should have rise and
fall times faster than 1μs. Do not leave pin fl oating. See
synchronizing section in Applications Information.
PG (Pin 7): The PG pin is the open collector output of an
internal comparator. PG remains low until the FB pin is
within 9% of the fi nal regulation voltage. PG output is valid
when V
is above 3.6V and RUN/SS is high.
IN
FB (Pin 8): The LT3693 regulates the FB pin to 0.790V.
Connect the feedback resistor divider tap to this pin.
(Pin 9): The VC pin is the output of the internal error
V
C
amplifi er. The voltage on this pin controls the peak switch
current. Tie an RC network from this pin to ground to
compensate the control loop.
RT (Pin 10): Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.
Exposed Pad (Pin 11): Ground. The Exposed Pad must
be soldered to PCB.
BLOCK DIAGRA
V
V
IN
IN
4
C1
RUN/SS
5
RT
10
R
T
SYNC
6
SOFT-START
PG
7
GND
11 8
W
INTERNAL 0.79V REF
ERROR AMP
+
0.7V
–
FB
R1
R2
–
BOOST
SW
BD
1
2
3
V
C
9
C3
L1
D1
C
C
C
F
R
C
C2
3693 BD
V
OUT
+
SLOPE COMP
5
OSCILLATOR
200kHzTO2.4MHz
+
–
SWITCH
LATCH
R
S
VC CLAMP
Q
3693f
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LT3693
OPERATION
The LT3693 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT,
enables an RS fl ip-fl op, turning on the internal power
switch. An amplifi er and comparator monitor the current
fl owing between the V
off when this current reaches a level determined by the
voltage at V
voltage through an external resistor divider tied to the FB
pin and servos the V
increases, more current is delivered to the output; if it
decreases, less current is delivered. An active clamp on the
pin provides current limit. The VC pin is also clamped to
V
C
the voltage on the RUN/SS pin; soft-start is implemented
by generating a voltage ramp at the RUN/SS pin using an
external resistor and capacitor.
An internal regulator provides power to the control circuitry.
The bias regulator normally draws power from the V
but if the BD pin is connected to an external voltage higher
than 3V bias power will be drawn from the external source
(typically the regulated output voltage). This improves
. An error amplifi er measures the output
C
and SW pins, turning the switch
IN
pin. If the error amplifi er’s output
C
pin,
IN
effi ciency. The RUN/SS pin is used to place the LT3693
in shutdown, disconnecting the output and reducing the
input current to less than 0.5μA.
The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate
the internal bipolar NPN power switch for effi cient operation.
The oscillator reduces the LT3693’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during startup
and overload.
The LT3693 contains a power good comparator which trips
when the FB pin is at 91% of its regulated value. The PG
output is an open-collector transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3693 is
enabled and V
is above 3.6V.
IN
8
3693f
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