LT1976/LT1976B
High Voltage 1.5A, 200kHz
Step-Down Switching Regulator
with 100μA Quiescent Current
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FEATURES
DESCRIPTIO
The LT®1976/LT1976B are 200kHz monolithic step-down
switching regulators that accept input voltages up to 60V.
A high efficiency 1.5A, 0.2Ω switch is included on the die
along with all the necessary oscillator, control and logic
circuitry. Current mode topology is used for fast transient
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Wide Input Range: 3.3V to 60V
1.5A Peak Switch Current (LT1976)
100μA Quiescent Current (LT1976)**
1.6mA Quiescent Current (LT1976B)
Low Shutdown Current: IQ < 1μA
Power Good Flag with Programmable Threshold
Load Dump Protection to 60V
200kHz Switching Frequency
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response and good loop stability.
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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
rangebyemployingBurstModeoperationatlowcurrents,
utilizing the output to bias the internal circuitry, and by
using a supply boost capacitor to fully saturate the power
switch. The LT1976B does not shift into Burst Mode
operation at low currents, eliminating low frequency out-
put ripple at the expense of 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 implemented
by driving the SYNC pin with logic-level inputs. A single
capacitor from the CSS pin to the output provides a
controlled output voltage ramp (soft-start). The devices
also have a power good flag with a programmable thresh-
old and time-out and thermal shutdown protection.
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Saturating Switch Design: 0.2Ω On-Resistance
Peak Switch Current Maintained Over
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Full Duty Cycle Range*
1.25V Feedback Reference Voltage
Easily Synchronizable
Soft-Start Capability
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Small 16-Pin Thermally Enhanced TSSOP Package
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APPLICATIO S
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High Voltage Power Conversion
14V and 42V Automotive Systems
Industrial Power Systems
Distributed Power Systems
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Battery-Powered Systems
, 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
The LT1976/LT1976B are available in a 16-pin TSSOP
package with Exposed Pad leadframe for low thermal
resistance.
**See Burst Mode Operation section for conditions
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TYPICAL APPLICATIO
LT1976 Supply Current vs
Input Voltage
LT1976 Efficiency and Power
Loss vs Load Current
14V to 3.3V Step-Down Converter with
100μA No Load Quiescent Current
150
100
75
50
25
0
10
V
= 3.3V
= 25°C
OUT
A
T
EFFICIENCY
V
3.3V
1A
OUT
125
100
75
50
25
0
V
IN
V
BOOST
SW
IN
3.3V TO 60V
1
4.7μF
100V
CER
33μH
0.33μF
4148
SHDN
5V
0.1μF
LT1976
3.3V
10MQ60N
0.1
C
SS
V
C
330pF
1500pF
10k
TYPICAL
POWER LOSS
V
BIAS
165k
47pF
FB
1%
100μF
6.3V
TANT
0.01
0.001
C
T
PGFB
PG
1μF
SYNC
GND
100k
1%
1976 TA01
0
10
20
30
40
50
60
0.1
1
10
100
1000 10000
INPUT VOLTAGE (V)
1976 F05
LOAD CURRENT (mA)
1976 TA02
1976bfg
1