SC1578 Ver la hoja de datos (PDF) - Semtech Corporation
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SC1578 Datasheet PDF : 5 Pages
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HIGH-EFFICIENCY STEP-DOWN
DC-DC CONVERTER
January 29, 1998
TYPICAL APPLICATION CIRCUIT
SC1578
Figure 3. Battery Charge Circuit with High-Side Current Sensing Constant Current Source
NOTE: RSENSE=0.1 ohm, charge current=0.5A ± 10%, VIN>VBATT + 3.5V
RSENSE=0.05 ohm, charge current=1A ± 10%, VIN>VBATT + 4V
RSENSE=0.033 ohm, charge current=1.5A ± 10%, VIN>VBATT + 4.5V
Efficiency>90%, measured at CS- node
PIN DESCRIPTIONS
PIN 1: VIN 4V to 24V input supply voltage.
PIN 2:
DUTY Duty cycle adjustment pin. To be tied
to the VIN pin directly or through a re-
sistor to adjust oscillator duty cycle.
See Electrical Characteristics: RDUTY
must be above 1MΩ if VIN>20V.
PIN 3:
SHDN Logical input to shutdown the chip:
VSHDN = high for normal operation,
VSHDN = low for shutdown.
This pin should not be left floating or
forced greater than 15V. In shutdown
mode the DRI pin is high.
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:
VOUT = 1.22 x (R1+R2)/R2
PIN 5: GND Power ground.
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 7: CS- Current sense comparator inverting
input, not to exceed VIN.
PIN 8: CS+ Current sense comparator non-
inverting input, not to exceed VIN.
© 1997 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
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