SC1462(2000) Ver la hoja de datos (PDF) - Semtech Corporation
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SC1462 Datasheet PDF : 9 Pages
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HIGH OUTPUT CURRENT
CHARGE PUMP DOUBLER
SC1462
October 20, 2000
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
THEORY OF OPERATION
The SC1462 utilizes a switched capacitor charge
pump, to generate an output voltage approximately
2xVin.
An internal oscillator generates two out of phase
fixed frequency clock signals which turn on and off
internal MOSFET switches. During phase1 of clock,
the flying charge pump capacitor is charged to Vin
through switches S1, and S2. During phase2 the
flying charge pump capacitor is connected in series
with the input voltage via S3, and S4, producing an
output voltage.
Charge transfer from Cin to C_charge
ON
S1,S2
OFF
ON
S3,S4
OFF
Charge transfer from (Cin,and C_charge) to Cout
OUTPUT CURRENT
The dropout voltage for a charge pump doubler is
defined as 2*Vin-Vout. The maximum output current
is usually specified as that which will not cause the
dropout voltage to exceed the requirements of the
application. The calculation of the dropout voltage is
given in the capacitor selection section on page 7.
Typical dropout voltages versus Iout are graphed on
page 8.
THERMAL SHUTDOWN
The thermal shutdown circuit provides added protec-
tion to the SC1462. During a VOUT short circuit condi-
tion or if the load is excessive , the over temperature
circuitry will shut down the charge pump if the junction
temperature exceeds approximately 140°C. The
charge pump is enabled only if the junction tempera-
ture drops to approximately 120°C. The SC1462 will
cycle in and out of thermal shut down until the short
circuit or the excessive load condition on Vout is
removed, therby improving device reliability. The junc-
tion temperature can be calculated from the following
formula if the ambient temperature (Ta) and the
charge pump power dissipation (Pdiss) are known.
Vin
Gnd
S1 C1+
C1-
S3
Cin
S4
C_charge
S2
Cout
Vout
TJ = Ta + Pdiss * θJA
;
Gnd
θJA = 230 °C/W
SHORT CIRCUIT / SOFT START
An internal current limit and soft start circuit provides
protection against output short circuit and limits large
current spikes generated during the initial start up to
charge output capacitor.
If VOUT is less than VIN - 200mV, then all switches are
turned off and VOUT is charged with a 200mA current
source from VIN. When VOUT reaches VIN - 200mV ,
the current source is disconnected from output and
the charge pump circuitry is enabled again.
© 2000 SEMTECH CORP.
6
652 MITCHELL ROAD NEWBURY PARK CA 91320
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