Linear Technology DC242 Demo Manual

DESCRIPTIO
Demonstration Circuit DC242 is a high input voltage, low
noise step-down (buck) regulator using the LT
switching regulator IC. Typical applications are automo-
tive cellular and GPS receivers, low noise telecom and
industrial-instrument power supplies. This controller in-
cludes an onboard 700mA peak-current switch and is
optimized for use with a high supply voltage. The input
voltage can range from 7.4V to 48V. In order to achieve low
noise, the LT1777 is equipped with dI/dt limiting circuitry,
which is programmed via a small external inductor in the
power path. It also contains internal circuitry to limit the
W U
PERFOR A CE SU
PARAMETER
Input Voltage Range
Output Voltage (Jumper Selectable)
Maximum Output Load Current
Typical Output Ripple Voltage
Nominal Operating Frequency
I , Supply Current in Shutdown
Q
≤ 12V and V
*I = 450mA for V
O IN
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
V Switching Waveforms
SW
V VOLTAGE
SW
10V/DIV
V CURRENT
SW
200mA/DIV
®
W W
ARY
T
A
CONDITIONS
I = 0mA to 500mA
OUT
V > 12V, V
IN
I = 500mA, V
OUT
V = 7.4V to 48V
IN
= 5V
OUT
W U
DC242 TA01
500ns/DIV
DEMO MANUAL DC242
Low Noise Step-Down
dV/dt turn-on and turn-off ramp rates. By slowing down
1777
the sharp edges during turn-on and turn-off of the power
switch, conducted and radiated EMI are significantly re-
duced. The output voltage is jumper selectable to either
3.3V or 5V. The LT1777 uses a 100kHz switching fre-
quency and current mode control, which offers excellent
dynamic input supply rejection and short-circuit protec-
tion. Additionally, the supply current can be shut down to
less than 30µA in standby mode. Gerber files for this
circuit are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
= 25°C
= 5V
OUT
= 24V
IN
U
DC/DC CONVERTER
LT1777 High Voltage,
DC/DC Converter
Component Side
VALUE
7.4V to 48V
3.3V, 5V
I = 500mA*
O
17mV
P-P
100kHz
30µA
1