ltc3440 Linear Technology Corporation, ltc3440 Datasheet - Page 6

• Manufacturer Part Number: ltc3440
• Description: Micropower Synchronous Buck-boost Dc/dc Converter
• Manufacturer: Linear Technology Corporation

PI FU CTIO S
LTC3440
R
Frequency. The programming frequency range is 300kHz
to 2MHz.
MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Syn-
chronization of the internal oscillator. A clock frequency of
twice the desired switching frequency and with a pulse
width between 100ns and 2μs is applied. The oscillator
free running frequency is set slower than the desired
synchronized switching frequency to guarantee sync. The
oscillator R
where f
SW1 (Pin 3): Switch Pin Where the Internal Switches A
and B are Connected. Connect inductor from SW1 to SW2.
An optional Schottky diode can be connected from SW1 to
ground. Minimize trace length to keep EMI down.
SW2 (Pin 4): Switch Pin Where the Internal Switches C
and D are Connected. For applications with output volt-
6
T
U
R
f
(Pin 1): Timing Resistor to Program the Oscillator
OSC
T
=
SW
=
8 10
U
6 10
•
= desired synchronized switching frequency.
f
T
SW
•
R
component value required is given by:
10
T
10
Hz
U
ages over 4.3V, a Schottky diode is required from SW2 to
V
GND (Pin 5): Signal and Power Ground for the IC.
V
capacitor is placed from V
V
ceramic bypass capacitor as close to the V
(Pin 5) is required.
SHDN/SS (Pin 8): Combined Soft-Start and Shutdown.
Grounding this pin shuts down the IC. Tie to >1.5V to
enable the IC and > 2.5V to ensure the error amp is not
clamped from soft-start. An RC from the shutdown com-
mand signal to this pin will provide a soft-start function by
limiting the rise time of the V
FB (Pin 9): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.5V to
5.5V. The feedback reference voltage is typically 1.22V.
V
network is connected from this pin to the FB pin to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.
Exposed Pad (Pin 11, DFN Package Only): Ground. This
pin must be soldered to the PCB and electrically connected
to ground.
OUT
OUT
IN
C
(Pin 10): Error Amp Output. A frequency compensation
(Pin 7): Input Supply Pin. Internal V
to ensure the SW pin does not exhibit excess voltage.
(Pin 6): Output of the Synchronous Rectifier. A filter
OUT
C
to GND.
pin.
CC
IN
for the IC. A
pin and GND
3440fb