MIC22400 Datasheet, PDF (11/19 Pages) Micrel Semiconductor – 4A Integrated Switch Synchronous Buck Regulator with Frequency Programmable up to 4MHz

Micrel, Inc.
Functional Description
PVIN
PVIN is the input supply to the internal 60mΩ P-Channel
Power MOSFET. This should be connected externally to
the SVIN pin. The supply voltage range is from 2.6V to
5.5V. A 10µF ceramic is recommended for bypassing
each PVIN supply.
EN
This pin is internally fed with a 1µA current source to
VIN. A delayed turn on is implemented by adding a
capacitor to this pin. The delay is proportional to the
capacitor value. The internal circuits are held off until EN
reaches the enable threshold of 1.24V.
RC
RC allows the slew rate of the output voltage to be
programmed by the addition of a capacitor from RC to
ground. RC is internally fed with a 1µA current source
and VOUT slew rate is proportional to the capacitor and
the 1µA source.
Delay
Adding a capacitor to this pin allows the delay of the
POR signal.
When VOUT reaches 90% of its nominal voltage, the
Delay pin current source (1µA) starts to charge the
external capacitor. At 1.24V, POR is asserted high.
Comp
The MIC22400 uses an internal compensation network
containing a fixed frequency zero (phase lead response)
and pole (phase lag response) which allows the external
compensation network to be much simplified for stability.
The addition of a single capacitor and resistor will add
the necessary pole and zero for voltage mode loop
stability using low value, low ESR ceramic capacitors.
MIC22400
FB
The feedback pin provides the control path to control the
output. A resistor divider connecting the feedback to the
output is used to adjust the desired output voltage. Refer
to the feedback section in the “Applications Information”
for more detail.
POR
This is an open drain output. A 47k resistor can be used
for a pull up to this pin. POR is asserted high when
output voltage reaches 90% of nominal set voltage and
after the delay set by CDELAY. POR is asserted low
without delay when enable is set low or when the output
goes below the -10% threshold. For a Power Good (PG)
function, the delay can be set to a minimum. This can be
done by removing the Delay capacitor.
SW
This is the connection to the drain of the internal P-
Channel MOSFET and drain of the N-Channel MOSFET.
This is a high frequency high power connection;
therefore traces should be kept as short and as wide as
practical.
CF
Adding a capacitor to this pin can adjust switching
frequency from 800kHz to 4MHz.
SGND
Internal signal ground for all low power sections.
PGND
Internal ground connection to the source of the internal
N-Channel MOSFETs.
February 2008
11
M9999-022108-A