LTC3125_15 Datasheet, PDF (6/18 Pages) Linear Technology – 1.2A Synchronous Step-Up DC/DC Converter with Input Current Limit

LTC3125
TYPICAL PERFORMANCE CHARACTERISTICS (T_A = 25°C unless otherwise noted)
V_OUT and I_IN During Soft-Start
V_OUT
2V/DIV
SHDN
5V/DIV
INPUT
CURRENT
200mA/DIV
V_IN = 3.3V
V_OUT = 4.5V
C_OUT = 1F
L = 2.7μH
2s/DIV
3125 G20
Efficiency vs V_IN
100
I_LOAD = 200mA
95 V_OUT = 3.8V
90
85
80
75
70
65
60
55
50
2
3
4
V_IN (V)
5
3125 G21
PIN FUNCTIONS
GND (Pin 1, Exposed Pad Pin 9): Ground. The exposed
pad must be soldered to the PCB ground plane for electrical
connection and for rated thermal performance.
FB (Pin 2): Feedback Input to the Error Amplifier. Connect
the resistor divider tap to this pin. The top of the divider
connects to V_OUT and the bottom of the divider connects
to GND. The output voltage can be adjusted from 1.8V
to 5.25V.
PROG (Pin 3): Programming Input for Average Input Cur-
rent. This pin should be connected to ground through an
external resistor (R_PROG) to set input average current limit
threshold. Refer to the Component Selection section in
Applications Information for details on selecting R_PROG.
V_IN (Pin 4): Input Voltage. The device is powered from V_IN
until V_OUT exceeds V_IN. Once V_OUT is greater than (V_IN +
0.25V), the device is powered from V_OUT. Place a ceramic
bypass capacitor from V_IN to GND. A minimum value of
1μF is recommended. Also connects to CS through 60mΩ
internal sense resistor.
CS (Pin 5): Current Sense Resistor Connection Point.
Connect the inductor directly to CS. An internal 60mΩ
sense resistor is connected between CS and V_IN.
SHDN (Pin 6): Logic Controlled Shutdown Input. Bringing
this pin above 1V enables the part, forcing this pin below
0.35V disables the part.
V_OUT (Pin 7): Output Voltage Sense and the Output of the
Synchronous Rectifier. Connect the output filter capacitor
from V_OUT to GND, close to the IC. A minimum value of
150μF is recommended. Due to the output disconnect
feature, V_OUT is disconnected from V_IN when SHDN is low.
SW (Pin 8): Switch Pin. Connect an inductor from this
pin to CS. An internal anti-ringing resistor is connected
across SW and CS after the inductor current has dropped
near zero.
3125fa
6