MIC2207 Datasheet, PDF (9/21 Pages) Micrel Semiconductor – 3mmx3mm 2MHz 3A PWM Buck Regulator

Micrel
Pin Descriptions
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 MIC2207. 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
R2
+
1⎟⎞
⎠
where V_REF is equal to 1.0V.
A feedforward capacitor is recommended for most
designs using the adjustable output voltage option.
To reduce current draw, a 10K feedback resistor is
recommended from the output to the FB pin (R1).
Also, a feedforward capacitor should be connected
between the output and feedback (across R1). The
large resistor value and the parasitic capacitance of
the FB pin can cause a high frequency pole that can
reduce the overall system phase margin. By placing
a feedforward capacitor, these effects can be
significantly reduced. Feedforward capacitance (C_FF)
can be calculated as follows:
C_FF
=
2π
1
× R1× 200kHz
MIC2205
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 Signal ground (SGND) 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
Micrel, Inc • 2180 Fortune Drive • San Jose, Ca 95131 • USA • tel [phone] • fax [phone] • http://www.micrel.com
April 2005
M9999-040705
www.micrel.com