SS6578CSTR datasheet(5/11 Pages) SSC

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SS6578

BLOCK DIAGRAM

70mV

Current Limit Comparator

Output

Driver

GND

DRI

CS+

CS-

VIN

PFM

OSC

1.22V

Reference

Voltage

Error

Comparator

DUTY

SHDN

VIN

LATCH

PIN DESCRIPTIONS

PIN 1: VIN

- Input supply voltage - a range of

4V to 18V is recommended.

PIN 2: DUTY - Duty cycle adjustment pin. To be

tied to the VIN pin directly or

through a resistor RDUTY to adjust

oscillator duty cycle. RDUTY must

be over 1M

Ω if V

IN=20V.

See TYPICAL PERFORMANCE

CHARACTERISTICS.

PIN 3:

SHDN- Logical input to shutdown the

chip:

VSHDN

High

for

normal

operation.

VSHDN = Low for shutdown.

This pin should not be floating or

forced

over

15V.

shutdown mode DRI pin is held

high.

PIN 4: FB

- Feedback comparator input, to

compare the feedback voltage

with the internal reference voltage.

Connecting

resistor

converter output node and a

resistor R2 to ground yields the

output voltage:

VOUT=1.22 x (R1+R2)/ R2

PIN 5: GND - Power ground.

PIN 6: DRI

- Push-pull driver output to drive an

external P-channel MOSFET or

PNP transistor. When driving a

PNP bipolar transistor, a base

resistor and a capacitor to the

base of PNP are recommended.

PIN 7: CS-

- Current-sense

comparator

inverting input. This pin voltage

should go over 2V but should

not exceed VIN voltage.

PIN 8: CS+ - Current

sense

comparator

non-inverting

input.

This

voltage should go over 2V but

should not exceed VIN voltage.

Rev.2.02 4/06/2004

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