LTC3125 Linear Technology, LTC3125 Datasheet - Page 6

• Manufacturer Part Number: LTC3125
• Description: 1.2A Synchronous Step-Up DC/DC Converter
• Manufacturer: Linear Technology

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PIN FUNCTIONS
LTC3125
TYPICAL PERFORMANCE CHARACTERISTICS
GND (Pin 1): Signal Ground.
FB (Pin 2): Feedback Input to the Error Amplifi er. Connect
the resistor divider tap to this pin. The top of the divider
connects to V
to GND. The output voltage can be adjusted from 1.8V
to 5.25V.
PROG (Pin 3): Programming Input for Average Input
Current. This pin should be connected to ground through
an external resistor (R
limit threshold. PROG pin gain = 22.1kΩ-A/A. The average
input current limit threshold is set by R
to the following:
V
until V
0.25V), the device is powered from V
bypass capacitor from V
1μF is recommended. Also connects to CS through 60mΩ
internal sense resistor.
6
IN
R
(Pin 4): Input Voltage. The device is powered from V
PROG
OUT
=
exceeds V
200mA/DIV
CURRENT
Desired I
OUT
2V/DIV
5V/DIV
INPUT
SHDN
V
22 1 .
OUT
and the bottom of the divider connects
V
V
C
L = 2.7μH
V
IN
OUT
OUT
OUT
k
IN
AVG
= 3.3V
Ω-A
PROG
. Once V
= 4.5V
= 1F
and I
IN
( )
) to set input average current
to GND. A minimum value of
A
IN
During Soft-Start
OUT
2s/DIV
is greater than (V
OUT
. Place a ceramic
PROG
3125 G20
according
IN
IN
+
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
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
Synchronous Rectifi er. Connect the output fi lter capaci-
tor from V
of 10μF ceramic is recommended. Due to the output
disconnect feature, V
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.
Exposed Pad (Pin 9): Power Ground. This pin must be
soldered to the PCB ground plane.
OUT
(Pin 7): Output Voltage Sense and the Output of the
100
90
85
80
70
50
95
75
65
60
55
Effi ciency vs V
2
OUT
(T
I
V
LOAD
OUT
A
= 25°C unless otherwise noted)
= 3.8V
to GND, close to the IC. A minimum value
= 200mA
3
OUT
IN
V
IN
is disconnected from V
(V)
4
3125 G21
5
IN
.
IN
when
3125f