Datasheet

LTC3442
6
3442fb
For more information www.linear.com/LTC3442
PIN FUNCTIONS
TYPICAL PERFORMANCE CHARACTERISTICS
(T
A
= 25°C unless otherwise specified).
Transition from Burst Mode
Operation to Fixed Frequency Mode
Pulsed Overload Using Average Input
Current Limit
200µs/DIV
3442 G22
C
OUT
= 100µF
LOW ESR TANTALUM
INDUCTOR
CURRENT
0.5A/DIV
V
OUT
50mV/DIV
1ms/DIV
3442 G23
R
LIM
= 133k
C
LIM
= .001µF
INDUCTOR
CURRENT
0.5A/DIV
R
LIM
PIN
0.5V/DIV
V
OUT
2V/DIV
SHDN/SS (Pin 1): Combined Soft-Start and Shutdown.
Applied voltage <0.4V shuts down the IC. Tie to >1.4V to
enable the IC and >2.4V to ensure the error amp is not
clamped from soft-start. For Burst Mode operation, this
pin must be pulled up to within 0.5V of V
IN
. An RC network
from the shutdown command signal to this pin will provide
a soft-start
function by limiting the rise time of the V
C
pin.
R
T
(Pin 2): Programs the Frequency of the Internal Os-
cillator. Place a resistor from this pin to ground. See the
Applications Information section for component value
selection.
SGND (Pin 3): Signal Ground for the IC.
SW1 (Pin 4): Switch Pin Where Internal Switches A and B
Are Connected. Connect inductor from SW1 to SW2. An
optional Schottky
diode can be connected from SW1 to
ground for a moderate efficiency improvement. Minimize
trace length to reduce EMI.
PGND (Pin 5, 13): Power Ground for the Internal NMOS
Power Switches. The exposed pad must be soldered to
PCB ground to provide both electrical contact and a good
thermal contact to the PCB.
SW2 (Pin 6): Switch Pin Where Internal Switches C
andD Are Connected. An optional Schottky
diode can be
connected from SW2 to V
OUT
for a moderate efficiency
improvement. Minimize trace length to reduce EMI.
BURST (Pin 7): Used to Set the Automatic Burst Mode Op-
eration Threshold. Place a resistor and capacitor in parallel
from this pin to ground. See the Applications Information
section for component value selection. For manual control,
ground the pin to force Burst Mode operation, connect to
V
OUT
to force fixed frequency mode.
V
OUT
(Pin 8): Output of the Synchronous Rectifier. A filter
capacitor is placed from V
OUT
to GND. A ceramic bypass
capacitor is recommended as close to the V
OUT
and GND
pins as possible.
V
IN
(Pin 9): Input Supply Pin. Internal V
CC
for the IC. A
10µF ceramic capacitor is recommended as close to V
IN
and SGND as possible.
R
LIM
(Pin 10): Sets the Average Input Current Limit
Threshold. Place a resistor and capacitor in parallel from
this pin to ground. See the Applications Information sec-
tion for component value selection.
V
C
(Pin 11): Error Amp Output. A frequency compensation
network is connected from this pin to FB to compensate
the loop. During Burst Mode operation, V
C
is internally
connected to a hold circuit.
FB (Pin 12):
Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to
5.25V. The feedback reference voltage is typically 1.22V.