© 1997 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

HIGH-EFFICIENCY STEP-DOWN

DC-DC CONVERTER

SC1578

January 29, 1998

PIN DESCRIPTIONS

PIN 1:

V

IN

4V to 24V input supply voltage.

PIN 5:

GND Power ground.

PIN 2:

DUTY Duty cycle adjustment pin. To be tied

to the V

sistor to adjust oscillator duty cycle.

See Electrical Characteristics: R

DUTY

must be above 1M

Ω if V

PIN 6:

DRI

Push-Pull driver output to drive an ex-

ternal P-channel MOSFET or PNP

transistor. When driving a PNP bipolar

transistor, a base resistor and a capac-

itor to the base of PNP are recom-

mended.

PIN 3:

SHDN Logical input to shutdown the chip:

V

V

This pin should not be left floating or

forced greater than 15V. In shutdown

mode the DRI pin is high.

PIN 7:

CS-

Current sense comparator inverting

input, not to exceed V

PIN 4:

FB

Feedback comparator input, to com-

pare the feedback voltage with the in-

ternal reference voltage. Connecting a

resistor R1 to the converter output and

a resistor R2 to ground yields the out-

put voltage:

V

PIN 8:

CS+

Current sense comparator non-

inverting input, not to exceed V

Figure 3. Battery Charge Circuit with High-Side Current Sensing Constant Current Source

NOTE: R

R

R

Efficiency>90%, measured at CS- node

TYPICAL APPLICATION CIRCUIT