LT1777
Low Noise Step-Down
Switching Regulator
FEATURES
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DESCRIPTIO
Programmable dI/dt Limit
Internally Limited dV/dt
High Input Voltage: 48V Max
700mA Peak Switch Rating
True Current Mode Control
100kHz Fixed Operating Frequency
Synchronizable to 250kHz
Low Supply Current in Shutdown: 30µA
Low Thermal Resistance 16-Pin SO Package
The LT
®
1777 is a Buck (step-down) regulator designed for
noise sensitive applications. It contains a dI/dt limiting
circuit programmed via a small external inductor in the
switching path. Internal circuitry also generates controlled
dV/dt ramp rates.
The monolithic die includes all oscillator, control and
protection circuitry. The part can accept operating input
voltages as high as 48V, and contains an output switch
rated at 700mA peak current. Current mode control offers
excellent dynamic input supply rejection and short-circuit
protection. The internal control circuitry is normally pow-
ered via the V
CC
pin, thereby minimizing power drawn
directly from the V
IN
supply (see Applications Informa-
tion). The fused-lead SO16 package and 100kHz switch-
ing frequency allow for minimal PC board area
requirements.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Automotive Cellular and GPS Receivers
Telecom Power Supplies
Industrial Instrument Power Supplies
TYPICAL APPLICATIO
Low Noise 5V Step-Down Supply
V
IN
24V
+
10
39µF
63V
100pF
12
14
100pF 12k
SGND
2200pF
7
12.1k
1%
1777 TA01
3
V
IN
SHDN
V
CC
V
SW
V
D
FB
LT1777
SYNC
V
C
4
1µH*
6
5
13
MBRS1100
220µH
V
OUT
5V
400mA
100µF
10V
36.5k
1%
V
SW
VOLTAGE
10V/DIV
+
V
SW
CURRENT
200mA/DIV
1777 TA02
*PROGRAMS dI/dT
U
V
SW
Switching Waveforms
500ns/DIV
U
U
1
LINER [ LINEAR TECHNOLOGY ]
