SC4911IMSTR datasheet(10/14 Pages) SEMTECH

10 / 14 page

 2006 Semtech Corp.

www.semtech.com

SC4911

POWER MANAGEMENT

Typical Applications (Cont.)

48V to 12V FLYBACK CONVERTER AS BATTERY

CHARGER

Figure 5 is another example of non-isolated feedback,

low power and compact application of the SC4911 as a

battery charger. Battery charging rate is determined by

current sense resistor R8. LUVLO is used to not only turn

on or turn off the charger by battery charge controller,

but also monitors the input line voltage via resistor R2

and R5 to determine turn-on and turnoff of the converter.

During the start-up, the input source trickle charges the

capacitor C3 through start-up resistor R1. As long as

voltage across C3 reaches the Vcc turn-on threshold,

the SC4911 turns on abruptly and starts driving the gate

of MOSFET Q1. After the SC4911 starts up the secondary

winding supplies the primary circuitry.

Si2320DS

150pF

To Battery Charger Controller

U1 SC4911

LUVLO

COMP

ILIM

GND

OUT

VCC

1000pF

100K

1.00

D1 1N5819

2.7MEG

R10

100K

Vin = 48V

10uF

4.7K

To 12V Battery

619K

D2 1N5819

47uF

100K

10uF

47nF

100K

Figure 5. 48V to 12V Flyback Converter as Battery Charger

In this application, voltage feedback is directly brought

from the output to the input error amplifier of SC4911

through R4 and R7. C5 and R9 are for frequency

compensation.

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