LT1977 Datasheet, PDF (1/24 Pages) Linear Technology – High Voltage 1.5A, 500kHz Step-Down Switching Regulator with 100uA Quiescent Current

LT1977
High Voltage 1.5A, 500kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
DESCRIPTIO
■ _{Wide Input Range: 3.3V to 60V}
■ _{1.5A Peak Switch Current}
■ _{Burst Mode}^® _{Operation: 100µA Quiescent Current**}
■ _{Low Shutdown Current: IQ < 1µA}
■ _{Power Good Flag with Programmable Threshold}
■ _{Load Dump Protection to 60V}
■ _{500kHz Switching Frequency}
■ _{Saturating Switch Design: 0.2Ω On-Resistance}
■ _{Peak Switch Current Maintained Over}
Full Duty Cycle Range*
■ _{1.25V Feedback Reference Voltage}
■ _{Easily Synchronizable}
■ _{Soft-Start Capability}
■ _{Small 16-Pin Thermally Enhanced TSSOP Package}
U
APPLICATIO S
■ _{High Voltage Power Conversion}
■ _{14V and 42V Automotive Systems}
■ _{Industrial Power Systems}
■ _{Distributed Power Systems}
■ _{Battery-Powered Systems}
, 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 and 6,531,909 **See Burst Mode Operation section for conditions
The LT^®1977 is a 500kHz 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 C_SS 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 LT1977 is available in a 16-pin TSSOP package with
exposed pad leadframe for low thermal resistance. The
LT1976, a 200kHz reduced switch frequency version of the
LT1977, is also available. See the Applications Information
section for selection criteria between the LT1976 and
LT1977.
TYPICAL APPLICATIO
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
V_IN
1500pF
26k
2.2µF
100V
CER
330pF
1µF
V_IN BOOST
SHDN
SW
0.1µF 10µH _1N4148
LT1977
0.1µF
10MQ100N
V_C
C_SS
C_T
SYNC
GND
V_BIAS
FB
PGFB
PG
10pF
165k
1% ₊
100k
1%
V_OUT
3.3V
1A
100µF
6.3V
TANT
1977 TA01
Supply Current vs Input Voltage
150
V_OUT = 3.3V
T_A = 25°C
125
100
75
50
25
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
1977 F05
Efficiency and Power Loss
vs Load Current
100 _{VIN = 12V}
10
EFFICIENCY
5V
75
1
3.3V
50
0.1
TYPICAL
POWER LOSS
25
0.01
0
0.0001 0.001 0.01 0.1
LOAD CURRENT (A)
0.001
1
10
1977 TA02
1977f
1