LT3437
High Voltage 500mA, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
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DESCRIPTIO
Wide Input Range: 3.3V to 60V
Load Dump (Input Transient) Protection to 80V
500mA Peak Switch Current
Burst Mode
®
Operation: 100µA Quiescent Current**
Low Shutdown Current: I
Q
< 1µA
Burst Mode Operation Defeat
200kHz Switching Frequency
Saturating Switch Design: 0.8Ω On-Resistance
Peak Switch Current Maintained Over
Full Duty Cycle Range*
1.25V Feedback Reference Voltage
Easily Synchronizable
Soft-Start Capability
Small 10-Pin Thermally Enhanced DFN Package
The LT
®
3437 is a 200kHz monolithic buck switching
regulator that accepts input voltages up to 80V. A high
efficiency 500mA, 0.8Ω switch is included on the die along
with all the necessary oscillator, control and logic cir-
cuitry. Current mode topology is used for fast transient
response and good loop stability.
Innovative design techniques along with a new high volt-
age process achieve high efficiency over a wide input
range. Efficiency is maintained over a wide output current
range by employing Burst Mode operation at low currents,
utilizing the output to bias the internal circuitry, and by
using a supply boost capacitor to fully saturate the power
switch. Burst Mode operation can be defeated by a logic
high signal on the SYNC pin which results in lower light
load ripple at the expense of light load efficiency. Patented
circuitry maintains peak switch current over the full duty
cycle range.* Shutdown reduces input supply current to
less than 1µA. External synchronization can be imple-
mented by driving the SYNC pin with logic-level inputs. A
single capacitor from the C
SS
pin to the output provides a
controlled output voltage ramp (soft-start).
The LT3437 is available in a low profile (0.75mm) 3mm
×
3mm 10-pin DFN package or a 16-Pin TSSOP Package
both with exposed pad leadframes for low thermal
resistance.
APPLICATIO S
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High Voltage Power Conversion
14V and 42V Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery-Powered Systems
Powered Ethernet
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. *Protected by U.S. Patents including 6498466. **See
Burst Mode Operation section for conditions.
TYPICAL APPLICATIO
V
IN
4.5V TO 80V*
V
IN
SHDN
LT3437
V
C
1500pF
25k
SYNC
GND
FB
330pF
C
SS
V
BIAS
27pF
BOOST
0.1µF
SW
0.1µF
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
SUPPLY CURRENT (µA)
2.2µF
100V
CER
100µH BAS21
10MQ100N
V
OUT
3.3V
400mA
Supply Current vs Input Voltage
200
180
160
140
120
100
80
60
40
20
3437 TA01
165k
100k
100µF
6.3V
TANT
*FOR INPUT VOLTAGES ABOVE 60V RESTRICTIONS APPLY
0
0
10
20
30 40 50 60
INPUT VOLTAGE (V)
70
80
3435 TA02
U
Input Voltage
Transient Response
V
IN
20V/DIV
V
IN
0V
V
OUT
20mV/DIV
AC COUPLED
I
OUT
250mA
LOAD DUMP
50ms/DIV
COLD CRANK
3437 TA03
U
U
3437f
1
LT3437
ABSOLUTE
(Note 1)
AXI U RATI GS
Operating Junction Temperature Range
LT3437EDD (Note 2) ....................... – 40°C to 125°C
LT3437IDD (Note 2) ........................ – 40°C to 125°C
LT3437EFE (Note 2) ........................ – 40°C to 125°C
LT3437IFE (Note 2) ......................... – 40°C to 125°C
Storage Temperature Range ................. – 65°C to 125°C
V
IN
, SHDN, BIAS, SW Operating ............................. 60V
V
IN
, SHDN 100ms Transient, <15% Duty Cycle ....... 80V
BOOST Pin Above SW ............................................ 35V
BOOST Pin Voltage Operating ................................. 75V
BOOST Pin 100ms Transient, <15% Duty Cycle ...... 85V
SYNC, C
SS
, FB .......................................................... 6V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SW
V
IN
BST
GND
C
SS
1
2
3
4
5
11
10 SHDN
9 SYNC
8 FB
7 V
C
6 BIAS
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO GND (PIN 4)
ORDER PART NUMBER
LT3437EDD
LT3437IDD
Order Options
Tape and Reel: Add #TR
DD PART MARKING
LBDJ
LBDK
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BIAS = 5V, FB = 1.25V,
C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
V
SHDN
I
SHDN
I
VINS
PARAMETER
SHDN Threshold
SHDN Input Current
Minimum Input Voltage (Note 3)
Supply Shutdown Current
Supply Sleep Current (Note 4)
I
VIN
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V
BIAS = 0V, FB = 1.35V
FB = 1.35V
BIAS = 0V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
BIAS = 5V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
SHDN = 12V
2
U
U
W
W W
U
W
TOP VIEW
NC
SW
NC
V
IN
NC
BOOST
NC
GND
1
2
3
4
5
6
7
8
17
16 NC
15 SHDN
14 SYNC
13 NC
12 FB
11 V
C
10 BIAS
9
C
SS
FE PACKAGE
16-LEAD PLASTIC TSSOP
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO GND (PIN 8)
ORDER PART NUMBER
LT3437EFE
LT3437IFE
FE PART MARKING
3437EFE
3437IFE
MIN
1.15
●
●
TYP
1.3
5
2.5
0.1
300
25
1.35
0.475
2.7
MAX
1.45
30
3
2
500
50
2
1
3.15
UNITS
V
µA
V
µA
µA
µA
mA
mA
V
3437f
LT3437
ELECTRICAL CHARACTERISTICS
SYMBOL
I
BIASS
I
BIAS
PARAMETER
BIAS Sleep Current (Note 4)
BIAS Quiescent Current
Minimum Boost Voltage (Note 6)
Input Boost Current (Note 7)
V
REF
I
FB
Reference Voltage (V
REF
)
FB Input Bias Current
EA Voltage Gain (Note 8)
EA Voltage g
m
EA Source Current
EA Sink Current
V
C
to SW g
m
V
C
Switching Threshold
V
C
High Clamp
I
PK
SW V
CESAT
SW Current Limit
Switch Saturation Voltage
(Note 9)
Switching Frequency
Maximum Duty Cycle
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Impedance
I
CSS
C
SS
Current Threshold (Note 10)
FB = 0V
4
240
50
10
16
I
SW
= 250mA
I
SW
= 500mA
●
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BIAS = 5V, FB = 1.25V,
C
SS
/SYNC = 0V unless otherwise noted.
CONDITIONS
●
MIN
TYP
150
0.75
1.8
11
8
MAX
250
1
2.5
16
13
1.275
200
UNITS
µA
mA
V
mA
mA
V
nA
V/V
µMho
SYNC = 2V
I
SW
= 250mA
I
SW
= 0.5A
I
SW
= 0.25A
3.3V < V
VIN
< 80V
●
1.225
1.25
50
900
dI(V
C
)=
±10µA
FB = 1.15V
FB = 1.35V
V
SYNC
= 2V
1.5
500
15
15
650
35
30
1
500
1.75
650
200
400
170
200
95
1.5
2
700
2.1
900
400
800
240
55
55
µA
µA
A/V
mV
V
mA
mV
mV
kHz
%
V
kHz
kΩ
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
The LT3437EDD/LT3437EFE 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
LT3437IDD/LT3437IFE are guaranteed and tested over the full –40°C to
125°C operating junction temperature range.
Note 3:
Minimum input voltage is defined as the voltage where switching
starts. Actual minimum input voltage to maintain a regulated output will
depend upon output voltage and load current. See Applications Information.
Note 4:
Supply input current is the quiescent current drawn by the input
pin. Its typical value depends on the voltage on the BIAS pin and operating
state of the LT3437. With the BIAS pin at 0V, all of the quiescent current
required to operate the LT3437 will be provided by the V
IN
pin. With the
BIAS voltage above its minimum input voltage, a portion of the total
quiescent current will be supplied by the BIAS pin. Supply sleep current is
defined as the quiescent current during the “sleep” portion of Burst Mode
operation. See Applications Information for determining application supply
currents.
Note 5:
Minimum BIAS voltage is the voltage on the BIAS pin when I
BIAS
is
sourced into the pin.
Note 6:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 7:
Boost current is the current flowing into the BOOST pin with the pin
held 3.3V above input voltage. It flows only during switch on time.
Note 8:
Gain is measured with a V
C
swing from 1.15V to 750mV.
Note 9:
Switch saturation voltage guaranteed by correlation to wafer level
measurements for DD package parts.
Note 10:
The C
SS
threshold is defined as the value of current sourced into the
C
SS
pin which results in an increase in sink current from the V
C
pin. See the
Soft-Start section in Applications Information.
3437f
3
LT3437
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency and Power Loss
vs Load Current
100
60
50
40
300
250
200
150
1.26
FREQUENCY (kHz)
EFFICIENCY (%)
FB VOLTAGE (V)
V
IN
= 12V
90
V
OUT
= 3.3V
T
A
= 25°C
80
70
EFFICIENCY
30
20
10
0
0.1
POWER LOSS
1
10
100
LOAD CURRENT (mA)
SHDN Threshold
1.50
1.45
1.40
VOLTAGE (V)
I
SHDN
(µA)
1.35
1.30
1.25
1.20
CURRENT (µA)
1.15
1.10
–50 –25
50
25
0
75
TEMPERATURE (°C)
Input Current vs Temperature
700
600
500
I
VIN
(µA)
RUN MODE
I
BIAS
(µA)
700
600
PEAK SWITCH CURRENT (mA)
400
300
200
100
SLEEP MODE V
BIAS
= 0V
SLEEP MODE V
BIAS
= 5V
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
4
U W
3437 G01
FB Voltage vs Temperature
500
450
400
350
Oscillator Frequency
vs Temperature
250
240
1.30
1.28
POWER LOSS (mW)
230
220
210
200
190
180
170
160
1.24
100
50
0
1000
1.22
1.20
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
150
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3437 G02
3437 G03
SHDN Pin Current
10
10
9
Shutdown Supply Current
vs Temperature
8
8
7
6
6
5
4
3
V
VIN
= 80V
V
VIN
= 60V
4
2
2
1
V
VIN
= 12V
0
100
125
0
10
20
30
V
SHDN
(V)
40
50
60
3437 G05
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3437 G04
3437 G06
Bias Current vs Temperature
900
800
RUN MODE
700
600
500
400
300
200
100
800
Switch Peak Current Limit
vs Temperature
500
400
300
200
100
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
SLEEP MODE
0
–50 –25
–0
25
50
75
TEMPERATURE (°C)
100
125
3437 G07
3437 G08
3437 G09
3437f
LT3437
TYPICAL PERFOR A CE CHARACTERISTICS
Soft-Start Current Threshold
vs FB Voltage
35
SOFT-START DEFEATED
30
200
FREQUENCY (kHz)
25
I
CSS
(µA)
20
15
10
5
0
0
0.2
0.6
0.8
0.4
FB VOLTAGE (V)
1.0
1.2
3437 G10
150
VOLTAGE (mV)
Supply Current vs Input Voltage
200
180
160
V
OUT
= 3.3V
7.5
7.0
6.5
SUPPLY CURRENT (µA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
140
120
100
80
60
40
20
0
0
10
20
30 40 50 60
INPUT VOLTAGE (V)
70
80
Minimum On-Time
500
450
400
11
12
BOOST CURRENT (mA)
350
ON-TIME (ns)
10
9
8
7
6
100
OUTPUT VOLTAGE (V)
300
250
200
150
100
50
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
U W
3437 F13
Oscillator Frequency
vs FB Voltage
250
Switch On Voltage (V
CESAT
)
600
500
400
300
200
100
0
100
T
J
= 25°C
T
J
= –40°C
T
J
= 125°C
100
50
0
0
0.25
0.75
0.50
FB VOLTAGE (V)
1.00
1.25
3437 G11
400
300
200
LOAD CURRENT (mA)
500
3437 G12
Minimum Input Voltage
200
5V TO START
180
160
5V TO RUN
140
120
100
80
60
40
3.3V TO RUN
0
100
200
300
400
LOAD CURRENT (mA)
500
3437 G14
Burst Mode Threshold
vs Input Voltage
V
OUT
= 3.3V
6.0
5.5
5.0
4.5
4.0
3.5
3.0
ENTER
EXIT
3.3V TO START
20
0
0
10
40
30
20
INPUT VOLTAGE (V)
50
60
3437 G15
Boost Current vs Load Current
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
400
300
200
LOAD CURRENT (mA)
500
3437 G17
Dropout Operation
V
OUT
= 3.3V
I
LOAD
= 250mA
BOOST DIODE =
DIODES INC B1100
0
2.0
2.5
3.0
3.5
INPUT VOLTAGE (V)
4.0
4.5
3437 G18
3437 G16
3437f
5
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