LTC1504A
PIN FUNCTIONS
I
MAX
(Pin 1):
Current Limit Set. Connect a resistor from
V
CC
to I
MAX
to set the current limit threshold. An internal
12µA current source from I
MAX
to GND sets the voltage
drop across this resistor. This voltage is compared to the
voltage drop across the internal high-side switch (Q1)
while it is turned on. See the Applications Information
section for more information. To disable current limit,
leave I
MAX
floating.
V
CC
(Pin 2):
Power Supply Input. Connect to a power
supply voltage between 4V and 10V. V
CC
requires a low
impedance bypass capacitor to ground, located as close
as possible to the LTC1504A. See the Applications Infor-
mation section for details on capacitor selection and
placement.
SW (Pin 3):
Power Switch Output. This is the switched
node of the buck circuit. Connect SW to one end of the
external inductor. The other end of the inductor should be
connected to C
OUT
and becomes the regulated output
voltage. Avoid shorting SW to GND or V
CC
.
GND (Pin 4):
Ground. Connect to a low impedance ground.
The input and output bypass capacitors and the feedback
resistor divider (adjustable parts only) should be grounded
as close to this pin as possible. Pin 4 acts as a heat sink
in the LTC1504A S0-8 package and should be connected
to as large a copper area as possible to improve thermal
dissipation. See the Thermal Considerations section for
more information.
FB (LTC1504A) (Pin 5):
Feedback. Connect FB to a resistor
divider from V
OUT
to GND to set the regulated output
voltage. The LTC1504A feedback loop will servo the FB pin
to 1.265V.
SENSE (LTC1504A-3.3) (Pin 5):
Output Voltage Sense.
Connect directly to the output voltage node. The
LTC1504A-3.3 feedback loop will servo SENSE to 3.3V.
SENSE is connected to an internal resistor divider which
will load any external dividers. For output voltages other
than 3.3V, use the LTC1504A.
SHDN (Pin 6):
Shutdown, Active Low. When SHDN is at a
logic High, the LTC1504A will operate normally. When
SHDN is Low, the LTC1504A ceases all internal operation
and supply current drops below 1µA. In shutdown, the SW
pin is pulled low. This ensures that the output is actively
shut off when SHDN is asserted, but it prevents other
supplies from providing power to the output when the
LTC1504A is inactive. See the Applications Information
section for more details.
SS (Pin 7):
Soft Start. Connect an external capacitor
(usually 0.1µF) from SS to GND to limit the output rise time
during power-up. C
SS
also compensates the current limit
loop, allowing the LTC1504A to enter and exit current limit
cleanly. See the Applications Information section for more
details.
COMP (Pin 8):
External Compensation. An external RC
network should be connected to COMP to compensate the
feedback loop. COMP is connected to the output of the
internal error amplifier.
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