SC21152 datasheet(14/18 Pages) SEMTECH

14 / 18 page

SC21152

25°C. Note that RDS

ON is a function of both VIN and

temperature.

The automatic discharge feature can optionally be dis-

abled from the device.

Over-current Protection

The SC21152 provides overload protection through pulse

by pulse current limiting. During the high-side on-time,

the high-side switches off if the inductor current exceeds

2.2A typically. The low-side turns on briefly, followed by

the next high-side on-time. Switching continues while

the output overload exists. When the overload is removed,

the SC21152 will resume normal operation. If the over-

load causes high junction temperature, the SC21152 will

go into Over-temperature protection.

Over-temperature Protection

The SC21152 will shut down if the junction temperature

exceeds typically 160 °C. The device will automatically

restart after the junction temperature has dropped typi-

cally 10 °C.

Component Selection

The SC21152 is optimized for use with components as

shown in the Detailed Applications Circuit on page 10.

Inductor: the inductor should be 0.47uH and capable of

supporting a minimum current of 1.2A.

Input capacitor: ceramic capacitor, minimum 4.7uF, X5R

or X7R or better dielectric.

Output capacitor: ceramic capacitor, minimum 10uF, X5R

or X7R or better dielectric.

Note when operating in Min Off mode, higher output

capacitance may needed to reduce output ripple when

VIN approaches VOUT.

The FB components provide output voltage sensing and

feedback compensation to regulate the output. The

output voltage is programmed using two resistor along

with a compensation capacitor.

Applications Information (continued)

Rtop

To FB pin

Rbot

VOUT

Ctop

To FB pin

The FB regulation setpoint is 800mV. The output voltage

can be calculated as shown.

The FB resistor values can be calculated as shown. It is

recommended to use 100kΩ for Rbot to minimize power

loss in the FB network.

The optimum value for Ctop is 22pF.

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