MIC25400 Datasheet, PDF (13/27 Pages) Micrel Semiconductor – 2A Dual Output PWM Synchronous Buck Regulator IC

Micrel, Inc.
R2 = ^{VREF × R1}
V_OUT − V_REF
Minimum Pulse Width
Output voltage is regulated by adjusting the on-time
pulse width of the high-side FET. This is accomplished
by comparing the error amplifier output with a sawtooth
waveform (see block diagram). The pulse width output of
the comparator becomes smaller as the error amplifier
voltage decreases. Due to propagation delay and other
circuit limitations, there is a minimum pulse width at the
output of the comparator. If the error amplifier voltage
drops any further, then the output of the comparator will
be low.
The PWM circuit will skip pulses if a smaller duty-cycle is
required to maintain output voltage regulation. This
effectively cuts the output frequency in half.
Thermal Protection
The internal temperature of the regulator is monitored to
prevent damage to the device. Both outputs are inhibited
from switching if the over-temperature threshold is
exceeded. Hysteresis in the circuit allows the regulator
to cool before turning back on.
MIC25400
January 2011
13
M9999-020111-C