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SC1404ITSTR Datasheet(PDF) 11 Page - Semtech Corporation

Part # SC1404ITSTR
Description  Mobile Multi-Output PWM Controller with Virtual Current Sense
PDF  27 Pages
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Manufacturer  SEMTECH [Semtech Corporation]
Direct Link  http://www.semtech.com
Logo SEMTECH - Semtech Corporation

SC1404ITSTR Datasheet(HTML) 11 Page - Semtech Corporation

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11
 2003 Semtech Corp.
www.semtech.com
SC1404
POWER MANAGEMENT
SC1404 Startup Sequence Chart
Reference Circuit Design
Introduction
The SC1404 is a versatile dual switching regulator with fixed 5V
and 3.3V outputs . In addition, there is an on-chip 5V linear regulator
capable of supplying 50mA output current and a 12V linear regulator
able to provide 200mA. The SC1404 is designed for notebook
applications but has is suited to applications where high efficiency,
small package, and low cost are required.
Design Guidelines
The schematic for the reference circuit is shown on page 22. The
reference circuit is configured as follows:
Switching Regulator 1
Vout1 = 3.3V @ 6A
Switching Regulator 2
Vout2 = 5.0V @ 6A
Linear Regulator 1
Vout3 = 12V, 200mA
Linear Regulator 2
Vout3 = 5.0V @ 50mA
Designing the Output Filter
Before calculating the output filter inductance and output
capacitance, an acceptable amount of output ripple current must
be determined. The maximum allowable ripple current depends
on the transient requirement of the power supply. Under normal
situation, the ripple current is usually set around 10 to 20% of the
Functional Information
maximum load. However, in order to speed up the output transient
response, ripple current can be much higher. In this design, we are
going to set the ripple current to be 40% of maximum load. So
once the ripple voltage specification is determined, the capacitor
ESR is chosen. The output ripple voltage is usually specified at +/
- 1% of the output voltage.
For the reference circuit 3.3V switcher, we selected a maximum
ripple voltage of 33mV. Choosing one 180uF, 4V Panasonic SP
Polymer Aluminum Electrolytic Cap, of which ESR is 15 Ω
m , sets
the maximum ripple current as follows:
Checking to see if the maximum RMS current can be met by the
SP cap.
Irms=0.635 A << Irms_rated=3.0A
The output inductance can now be found by:
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