LT3437
High Voltage 500mA, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
DESCRIPTIO
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.
FEATURES
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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
Defeatable Burst Mode Operation
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
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
, LT, LTC and LTM 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
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
SUPPLY CURRENT (µA)
V
IN
4.5V TO 80V*
Supply Current vs Input Voltage
200
V
OUT
3.3V
400mA
180
160
140
120
V
IN
20V/DIV
2.2µF
100V
CER
V
IN
SHDN
BOOST
0.1µF
SW
0.1µF
100µH BAS21
10MQ100N
LT3437
V
C
C
SS
100
80
60
1500pF
25k
330pF
V
BIAS
27pF
165k
SYNC
GND
FB
100k
100µF
6.3V
TANT
40
20
*FOR INPUT VOLTAGES ABOVE 60V RESTRICTIONS APPLY
3437 TA01
0
0
10
20
30 40 50
60
INPUT VOLTAGE (V)
70
80
3437 TA02
U
U
U
Input Voltage
Transient Response
V
IN
0V
V
OUT
20mV/DIV
AC COUPLED
I
OUT
250mA
LOAD DUMP
50ms/DIV
COLD CRANK
3437 TA03
3437fc
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
LT3437HFE (Note 2) .......................... –40°C to 140°C
Storage Temperature Range ................. – 65°C to 125°C
DD Package ....................................... –65°C to 125°C
FE Package ........................................ –65°C to 150°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
BOOST
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.
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the –40°C to 125°C
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)
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V, BIAS = 0V
BIAS = 0V, FB = 1.35V
FB = 1.35V
●
●
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
LT3437HFE
FE PART MARKING
3437EFE
3437IFE
3437HFE
MIN
1.15
●
●
TYP
1.3
5
2.5
0.1
150
45
MAX
1.45
30
3
2
300
75
UNITS
V
µA
V
µA
µA
µA
3437fc
LT3437
ELECTRICAL CHARACTERISTICS
SYMBOL
I
VIN
PARAMETER
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
I
BIASS
I
BIAS
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)
The
●
denotes the specifications which apply over the –40°C to 125°C
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
BIAS = 0V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
BIAS = 5V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
●
MIN
TYP
1.35
0.475
2.7
110
0.75
1.8
11
8
MAX
2
1
3.15
180
1
2.5
16
13
1.275
200
UNITS
mA
mA
V
µA
mA
V
mA
mA
V
nA
V/V
µMho
SYNC = 2V
I
SW
= 500mA
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
●
650
15
15
35
30
1
500
1.75
650
200
400
165
200
95
1.5
240
50
2
700
10
16
2.1
900
400
800
240
500
55
55
µA
µA
A/V
mV
V
mA
mV
mV
kHz
%
V
kHz
kΩ
µA
I
SW
= 250mA
I
SW
= 500mA
●
●
●
FB = 0V
4
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the –40°C to 140°C
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)
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V, BIAS = 0V
BIAS = 0V, FB = 1.35V
FB = 1.35V
●
●
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
1.1
●
●
TYP
1.3
5
2.5
0.1
150
45
MAX
1.5
30
3.5
2
300
75
UNITS
V
µA
V
µA
µA
µA
SHDN = 12V
3437fc
3
LT3437
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the –40°C to 140°C
I
VIN
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
I
BIASS
I
BIAS
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
●
●
●
●
●
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.
BIAS = 0V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
BIAS = 5V, FB = 1.15V, V
C
= 0.8V, SYNC = 2V
1.35
0.475
2.7
110
0.75
1.8
11
8
●
●
2
1
3.15
180
1
2.5
16
13
1.288
1.288
200
mA
mA
V
µA
mA
V
mA
mA
V
V
nA
V/V
µMho
SYNC = 2V
I
SW
= 500mA
I
SW
= 0.5A
I
SW
= 0.25A
3.3V < V
VIN
< 60V
V
VIN
= 80V
1.212
1.190
1.25
1.25
50
900
dI(V
C
)=
±10µA
FB = 1.15V
FB = 1.35V
V
SYNC
= 2V
1.5
400
15
15
650
35
30
1
500
1.75
650
200
400
140
200
95
1.5
2
500
2.1
900
400
800
240
55
55
µA
µA
A/V
mV
V
mA
mV
mV
kHz
%
V
kHz
kΩ
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 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. The LT3437HFE is also tested
to the LT3437 Electrical Characteristics table at 140°C operating junction
temperature. High junction temperatures degrade operating lifetimes.
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.
3437fc
4
LT3437
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency and Power Loss
vs Load Current
100
V
IN
= 12V
90 V
OUT
= 3.3V
T
A
= 25°C
80
70 EFFICIENCY
500
450
400
1.28
FREQUENCY (kHz)
1.30
EFFICIENCY (%)
FB VOLTAGE (V)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
POWER LOSS
SHDN Threshold
1.50
1.45
1.40
VOLTAGE (V)
I
SHDN
(µA)
8
10
CURRENT (µA)
1.35
1.30
1.25
1.20
1.15
1.10
–50 –25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
3437 G04
Input Current vs Temperature
600
500
400
I
VIN
(µA)
600
500
I
VIN
(µA)
400
300
PEAK SWITCH CURRENT (mA)
RUN MODE
300
200
100
SLEEP MODE V
BIAS
= 0V
SLEEP MODE V
BIAS
= 5V
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3437 G07
U W
FB Voltage vs Temperature
250
240
230
220
210
200
190
180
170
160
1.20
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3437 G02
Oscillator Frequency
vs Temperature
350
300
250
200
150
100
50
0
1000
3437 G01
POWER LOSS (mW)
1.26
1.24
1.22
150
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3437 G03
SHDN Pin Current
22
20
18
16
6
Shutdown Supply Current
vs Temperature
14
12
10
8
6
4
2
0
–50 –25
V
VIN
= 80V
V
VIN
= 60V
V
VIN
= 12V
0
25 50 75 100 125 150
TEMPERATURE (°C)
3437 G06
4
2
0
10
20
30
V
SHDN
(V)
40
50
60
3437 G05
Bias Current vs Temperature
800
700
RUN MODE
800
700
600
500
400
300
200
100
Switch Peak Current Limit
vs Temperature
200
SLEEP MODE
100
0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3437 G08
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3437 G09
3437fc
5
