MIC2204 Micrel, Inc.
M9999-042205 10 April 2005
PWM Operation
The MIC2204 is a pulsewidth modulation (PWM) controller.
By controlling the ratio of on-to-off time, or duty cycle, a
regulated DC output voltage is achieved. As load or supply
voltage changes, so does the duty cycle to maintain a
constant output voltage. In cases where the input supply runs
into a dropout condition, the MIC2204 will run at 100% duty
cycle.
The MIC2204 provides constant switching at 2MHz with
synchronous internal MOSFETs. The internal MOSFETs
include a high-side P-Channel MOSFET from the input
supply to the switch pin and an N-Channel MOSFET from the
switch pin to ground. Since the low-side N-Channel MOSFET
provides the current during the off cycle, a free wheeling
Schottky diode from the switch node to ground is not required.
PWM control provides fixed frequency operation. By main-
taining a constant switching frequency, predictable funda-
mental and harmonic frequencies are achieved. Other meth-
ods of regulation, such as burst and skip modes, have
frequency spectrums that change with load and can interfere
with sensitive communication equipment.
Synchronization
SYNC_IN allows the user to change the frequency from
2MHz up to 2.5MHz or down to 1.8MHz. This controls the
fundamental frequency and all the resultant harmonics. Main-
taining a predictable frequency creates the ability to either
shift the harmonics away from sensitive carrier and IF fre-
quency bands, or to accurately filter out specific harmonic
frequencies.
Connecting the SYNC_OUT function pin to the SYNC_IN of
other MIC2204s will synchronize multiple MIC2204s in a
daisy-chain. Synchronizing multiple MIC2204s means that
regulators will run at the same fundamental frequency, result-
ing in matched harmonic frequencies and simplifying design
for sensitive communication equipment.
