LT1976
High Voltage 1.5A, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
s Wide Input Range: 3.3V to 60V
s 1.5A Peak Switch Current
s Burst Mode® Operation: 100µA Quiescent Current**
s Low Shutdown Current: IQ < 1µA
s Power Good Flag with Programmable Threshold
s Load Dump Protection to 60V
s 200kHz Switching Frequency
s Saturating Switch Design: 0.2Ω On-Resistance
s Peak Switch Current Maintained Over
Full Duty Cycle Range*
s 1.25V Feedback Reference Voltage
s Easily Synchronizable
s Soft-Start Capability
s Small 16-Pin Thermally Enhanced TSSOP Package
U
APPLICATIO S
s High Voltage Power Conversion
s 14V and 42V Automotive Systems
s Industrial Power Systems
s Distributed Power Systems
s Battery-Powered Systems
DESCRIPTIO
The LT®1976 is a 200kHz monolithic buck switching
regulator that accepts 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 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. 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
device also has a power good flag with a programmable
threshold and time-out and thermal shutdown protection.
The LT1976 is available in a 16-pin TSSOP package with
exposed pad leadframe for low thermal resistance.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent 6,498,466 **See Burst Mode Operation section for conditions
TYPICAL APPLICATIO
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
VIN
3.3V TO 60V
0.047µF
12.5k
4.7µF
100V
CER
100pF
1µF
VIN BOOST
SHDN
SW
0.33µF 33µH 4148
LT1976 0.1µF
10MQ100N
VC CSS
CT
SYNC
GND
VBIAS
FB
PGFB
PG
27pF
165k
1%
100k
1%
VOUT
3.3V
1A
100µF
6.3V
TANT
1976 TA01
Supply Current vs
Input Voltage
150
VOUT = 3.3V
TA = 25°C
125
100
75
50
25
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
1976 F05
Efficiency vs Load Current
100
90
VOUT = 5V
80
TA = 25°C
70 VOUT = 3.3V
60
50
40
30
20
10
0
0.0001 0.001 0.01
0.1
LOAD CURRENT (A)
1
10
1976 TA02
1976f
1
