MIC2238_10 Datasheet, PDF (9/16 Pages) Micrel Semiconductor – 2.5MHz Dual Phase PWM Buck Regulator

Micrel, Inc.
Functional Block Diagram
MIC2238
Functional Description
VIN
VIN provides power to the MOSFETs for the switch
mode regulator section, along with the current limiting
sensing. Due to the high switching speeds, a 10µF
capacitor is recommended close to VIN and the power
ground (PGND) pin for bypassing. Please refer to layout
recommendations.
AVIN
Analog V_IN (AVIN) provides power to the analog supply
circuitry. AVIN and VIN must be tied together. Careful
layout should be considered to ensure high frequency
switching noise caused by VIN is reduced before
reaching AVIN. A 1µF capacitor as close to AVIN as
possible is recommended. See layout recommendations
for detail.
EN1
Enable 1 controls the on and off state of regulator 1. A
high logic on Enable 1 (EN1) activates regulator 1 while
a low logic deactivates regulator 1. MIC2238 features
built-in soft-start circuitry that reduces in-rush current
and prevents the output voltage from overshooting at
start up.
EN2
Enable 2 controls the on and off state of regulator 2. A
high logic on Enable 2 (EN2) activates regulator 2 while
a low logic deactivates regulator 2. MIC2238 features
built-in soft-start circuitry that reduces in-rush current
and prevents the output voltage from overshooting at
start up.
/FPWM
The Forced PWM Mode selects the mode of operation
for this device. Grounding this pin forces the device to
stay in constant frequency PWM mode only. Pulling this
pin high enables automatic selection of Trickle or PWM
mode operation, depending on the load. While /FPWM
is high and the load is below 100mA, the device will go
into Trickle mode. If the load is above 100mA, PWM
mode will automatically be selected. Do not leave this
pin floating.
PGOOD
The Power Good Output is pulled down unless the
regulator 1 output voltage is within +6.25% or -8.5% of
regulation. When the output voltage is in regulation, the
PGOOD capacitor will be charged to AVIN by an internal
5μA current source through a 1kΩ resistor. The charge
April 2010
9
M9999-040810-A