SC21152 Datasheet, PDF (14/18 Pages) Semtech Corporation – Tiny 1.2A Synchronous Buck Regulator with Power Good

SC21152
Applications Information (continued)
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.
VOUT
R to p
To FB pin ^Ctop
To FB pin
Rbot
The FB regulation setpoint is 800mV. The output voltage
can be calculated as shown.
9₂₈₇

u
¨§
©
5WRS
5ERW
¸·
¹
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.
5WRS
9287  9 u 5ERW
9
The optimum value for Ctop is 22pF.
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.
14