MIC2208 Datasheet, PDF (8/19 Pages) Micrel Semiconductor – 3mmx3mm 1MHz 3A PWM Buck Regulator

Micrel, Inc.
Pin Description
VIN
Two pins for VIN provide power to the source of the
internal P-channel MOSFET along with the current
limiting sensing. The VIN operating voltage range is
from 2.7V to 5.5V. Due to the high switching speeds,
a 10µF capacitor is recommended close to VIN and
the power ground (PGND) for each pin for
bypassing. Please refer to layout recommendations.
BIAS
The bias (BIAS) provides power to the internal
reference and control sections of the MIC2208. A 10
Ohm resistor from VIN to BIAS and a 0.1uF from
BIAS to SGND is required for clean operation.
EN
The enable pin provides a logic level control of the
output. In the off state, supply current of the device
is greatly reduced (typically <1µA). Do not drive the
enable pin above the supply voltage.
FB
The feedback pin (FB) provides the control path to
control the output. For adjustable versions, a resistor
divider connecting the feedback to the output is used
to adjust the desired output voltage. The output
voltage is calculated as follows:
V_OUT
=
V_REF
× ⎜⎛ ^R1 + 1⎟⎞
⎝ ^R2 ⎠
where V_REF is equal to 1.0V.
COMP
The COMP pin is the output of the internal error
amplifier. This pin is used to compensate the
MIC2208 for stability over a varying range of
MIC2208
external components. Refer to the compensation
section of the datasheet for determining nessasary
component values.
SW
The switch (SW) pin connects directly to the inductor
and provides the switching current nessasary to
operate in PWM mode. Due to the high speed
switching on this pin, the switch node should be
routed away from sensitive nodes. This pin also
connects to the cathode of the free-wheeling diode.
PGOOD
Power good is an open drain pull down that
indicates when the output voltage has reached
regulation. For a power good low, the output voltage
is within +/- 10% of the set regulation voltage. For
output voltages greater or less than 10%, the
PGOOD pin is high. This should be connected to the
input supply through a pull up resistor. A delay can
be added by placing a capacitor from PGOOD to
ground.
PGND
Power ground (PGND) is the ground path for the
MOSFET drive current. The current loop for the
power ground should be as small as possible and
separate from the Analog ground (AGND) loop.
Refer to the layout considerations fro more details.
SGND
Signal ground (SGND) is the ground path for the
biasing and control circuitry. The current loop for the
signal ground should be separate from the power
ground (PGND) loop. Refer to the layout
considerations for more details.
September 2005
8
M9999-092905
www.micrel.com