SC1462AISKTR View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC1462AISKTR' PDF : 9 Pages View PDF
5+ "$ )
POWER MANAGEMENT
Applications Information
THEORY OF OPERATION
The SC1462A 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 Cbucket
If VOUT is less than VIN - 200mV, then all switches are
turned off and VOUT is charged with a 100mA current source
from VIN. When VOUT reaches VIN - 200mV , the current
source is disconnected from output and the charge pump
circuitry is enabled again.
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 calcu-
lation of the dropout voltage is given in the capacitor se-
lection section on page 6. Typical dropout voltages versus
Iout are graphed on page 8.
ON
S1,S2
OFF
ON
S3,S4
OFF
Charge transfer from:
Cin and Cbucket to Cout (Doubler)
S1
1
2
S4 Vout = 2 x Vin
1
2
THERMAL SHUTDOWN
The thermal shutdown circuit provides added protection
to the SC1462A. During a VOUT short circuit condition 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 en-
abled only if the junction temperature drops to approxi-
mately 120°C. The SC1462A will cycle in and out of ther-
mal shut down until the short circuit or the excessive
load condition on Vout is removed, there by improving de-
vice reliability. The junction temperature can be calculated
from the following formula if the ambient temperature (Ta)
and the charge pump power dissipation (Pdiss) are known.
Cbucket
Cout
Vin
S3
S2
1
2
1
2
Cin
Doubler
TJ = Ta + Pdiss * θJA ; θJA = 230 °C/W
SHORT CIRCUIT / SOFT START
An internal current limit and soft start circuit provides pro-
tection against output short circuit and limits large cur-
rent spikes generated during the initial start up to charge
output capacitor.
2001 Semtech Corp.
5
www.semtech.com
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