4

LTC1504

Shutdown Threshold vs

Supply Voltage

SUPPLY VOLTAGE (V)

35

7

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

10

1504 • TPC07

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

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 1

µA. 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 0.1

µF)fromSStoGNDtolimittheoutputrisetime

12

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,

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

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 –25

0

25

50

75

1504 • TPC05

125

500

450

400

350

300

250

200

150

100

50

0

100