LT1777 Datasheet, PDF (1/24 Pages) Linear Technology – Low Noise Step-Down Switching Regulator

FEATURES
s _{Programmable dI/dt Limit}
s _{Internally Limited dV/dt}
s _{High Input Voltage: 48V Max}
s _{700mA Peak Switch Rating}
s _{True Current Mode Control}
s _{100kHz Fixed Operating Frequency}
s _{Synchronizable to 250kHz}
s _{Low Supply Current in Shutdown: 30µA}
s _{Low Thermal Resistance 16-Pin SO Package}
U
APPLICATIO S
s _{Automotive Cellular and GPS Receivers}
s _{Telecom Power Supplies}
s _{Industrial Instrument Power Supplies}
LT1777
Low Noise Step-Down
Switching Regulator
DESCRIPTIO
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.
TYPICAL APPLICATIO
Low Noise 5V Step-Down Supply
V_IN
24V ₊
10
39µF
63V
V_IN
3
4
SHDN V_CC
100pF
LT1777
1µH*
100pF 12k
12
SYNC
14
V_C
6
V_SW
5
V_D
13
FB
SGND
2200pF
7
220µH
+
MBRS1100
*PROGRAMS dI/dT
100µF
10V
V_OUT
5V
400mA
36.5k
1%
12.1k
1%
1777 TA01
V_SW
VOLTAGE
10V/DIV
V_SW
CURRENT
200mA/DIV
V_SW Switching Waveforms
500ns/DIV
1777 TA02
1