Datasheet

4
LTC1504
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
Shutdown Threshold vs
Supply Voltage
SUPPLY VOLTAGE (V)
357
SHUTDOWN PIN THRESHOLD (V)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
10
1504 • TPC07

PIN FUNCTIONS
UUU
as large a copper area as possible to improve thermal
dissipation. See the Thermal Considerations section for
more information.
FB (LTC1504CS8) (Pin 5): Feedback. Connect FB to a
resistor divider from V
OUT
to GND to set the regulated
output voltage. The LTC1504CS8 feedback loop will servo
the FB pin to 1.265V.
SENSE (LTC1504CS8-3.3) (Pin 5): Output Voltage Sense.
Connect directly to the output voltage node. The
LTC1504CS8-3.3 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 LTC1504CS8.
SHDN (Pin 6): Shutdown, Active Low. When SHDN is at a
logic High, the LTC1504 will operate normally. When
SHDN is Low, the LTC1504 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
LTC1504 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
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 LTC1504. See the Applications Informa-
tion 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 LTC1504 S0-8 package and should be connected to
Current Limit Threshold vs
Temperature
TEMPERATURE (°C)
–50
CURRENT LIMIT THRESHOLD (mA)
–25 0 25 50 75
1504 • TPC05
125
500
450
400
350
300
250
200
150
100
50
0
100
V
CC
= 5V
R
IMAX
= 47k
R
IMAX
= 22k