LTC3125_15 Datasheet, PDF (12/18 Pages) Linear Technology – 1.2A Synchronous Step-Up DC/DC Converter with Input Current Limit

LTC3125
APPLICATIONS INFORMATION
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.
Table 3.
STANDARD 1% RESISTOR VALUE
(K)
22.1
24.9
28.0
29.4
31.6
37.4
54.9
71.5
82.5
TYPICAL APPLICATION
INPUT LIMIT (A)
1.001
0.890
0.791
0.750
0.699
0.588
0.393
0.295
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
PC Card (3.3V/1000mA Maximum) 4.5V Output, GSM Pulsed Load
V_IN
PC CARD V_CC
3.3V ±10%
1000mA MAX
2.7μH*
10μF
CER
OFF ON
22.6k
CS
SW
V_IN
V_OUT
LTC3125
SHDN
PROG
FB
GND
V_OUT
4.5V, 2A PULSED LOAD
(577μs PW, 4.6ms PERIOD)
2.74M
2200μF**
s2
55mΩ
TANT
1M
3125 TA03a
*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
V_IN = 3.3V
V_OUT = 4.5V
C_OUT = 4.4mF
L = 2.7μH
R_PROG = 22.6k
1ms/DIV
3125 TA03b
3125fa
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