MIC2601 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – 1.2A, 1.2MHz/2MHz Wide Input Range Integrated Switch Boost Regulator

Micrel, Inc.
Functional Description
The MIC2601/2 is a constant frequency, PWM current
mode boost regulator. The block diagram is shown in
Figure 1. The MIC2601/2 is composed of an oscillator,
slope compensation ramp generator, current amplifier,
g_m error amplifier, PWM generator, and a 1.2A bipolar
output transistor. The oscillator generates a
1.2MHz/2MHz clock. The clock’s two functions are to
trigger the PWM generator that turns on the output
transistor and to reset the slope compensation ramp
generator. The current amplifier is used to measure the
switch current by amplifying the voltage signal from the
internal sense resistor. The output of the current
amplifier
is
summed
with the output of the slope compensation ramp
generator. This summed current-loop signal is fed to one
of the inputs of the PWM generator.
The g_m error amplifier measures the feedback voltage
through the external feedback resistors and amplifies the
error between the detected signal and the 1.25V
reference voltage. The output of the gm error amplifier
provides the voltage-loop signal that is fed to the other
input of the PWM generator. When the current-loop
signal exceeds the voltage-loop signal, the PWM
generator turns off the bipolar output transistor. The next
clock period initiates the next switching cycle,
maintaining the constant frequency current-mode PWM
control.
Pin Description
VIN
VIN provides power to the MOSFETs for the switch
mode regulator section. Due to the high switching
speeds, a 2.2µF capacitor is recommended close to VIN
and the power ground (PGND) pin for bypassing. Please
refer to layout recommendations.
VDD
The VDD pin supplies the power to the internal power to
the control and reference circuitry. The VDD is powered
from VIN. A small 0.1µF capacitor is recommended for
bypassing.
MIC2601/2
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 <0.1µA). Also, in the off state,
the output drive is placed in a "tri-stated" condition,
where bipolar output transistor is in an “off” or non-
conducting state. Do not drive the enable pin above the
supply voltage.
SS
The SS pin is the soft start pin which allows the
monotonic buildup of output when the MIC2601/2 comes
up during turn on. The SS pin gives the designer the
flexibility to have a desired soft start by placing a
capacitor SS to ground. A 0.1µF capacitor is used for in
the circuit.
FB
The feedback pin (FB) provides the control path to
control the output. For fixed output controller output is
directly connected to feedback (FB) pin.
SW
The switch (SW) pin connects directly to the inductor
and provides the switching current necessary to operate
in PWM mode. Due to the high speed switching and high
voltage associated with this pin, the switch node should
be routed away from sensitive nodes.
PGND
Power ground (PGND) is the ground path for the high
current PWM mode. 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 for more details.
AGND
Analog ground (AGND) 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 2009
8
M9999-090909-A