Datasheet

LTC3125
12
3125fa
PC Card (3.3V/1000mA Maximum) 4.5V Output, GSM Pulsed Load
CS
2.7µH*
LTC3125
GND
V
IN
2.74M
2200µF**
s2
55m
TANT
10µF
CER
V
OUT
4.5V, 2A PULSED LOAD
(577µs PW, 4.6ms PERIOD)
V
IN
PC CARD V
CC
3.3V ±10%
1000mA MAX
1M
3125 TA03a
SHDN
PROG
V
OUT
FB
22.6k
SW
OFF ON
*WURTH 7440420027
**VISHAY 592D228X6R3X220H
Waveforms of Input Current,
V
OUT
for Pulsed Load Current
V
OUT
100mV/DIV
INPUT CURRENT
500mA/DIV
LOAD CURRENT
2A/DIV
1ms/DIVV
IN
= 3.3V
V
OUT
= 4.5V
C
OUT
= 4.4mF
L = 2.7µH
R
PROG
= 22.6k
3125 TA03b
AVERAGE INPUT ILIMIT PROGRAMMING RESISTOR
SELECTION
The input current limit is user programmable by selection
of an external resistor, R
PROG
. It is important to locate
the resistor as close to the pin as possible to minimize
capacitance and noise pick-up. Resistor tolerance directly
affects the current limit accuracy so it must be factored in
to the application requirements. Table 3 shows standard
resistors for typical current limit values. Also refer to the
graph, “Average Input Current vs R
PROG
”, in the Typical
Performance Characteristics section of this datasheet.
APPLICATIONS INFORMATION
Table 3.
STANDARD 1% RESISTOR VALUE
(K)
TYPICAL APPLICATION
INPUT LIMIT (A)
22.1 1.001
24.9 0.890
28.0 0.791
29.4 0.750
31.6 0.699
37.4 0.588
54.9 0.393
71.5 0.295
82.5 0.252
For most applications the loss in accuracy from standard
1% resistors is tolerated but for critical applications the
use of 0.1% resistors is recommended.
TYPICAL APPLICATIONS