MIC2150 Datasheet, PDF (10/27 Pages) Micrel Semiconductor – 2-Phase Dual Output PWM Synchronous Buck Control IC

Micrel, Inc.
MIC2150
Functional Description
The MIC2150 is a dual channel, synchronous buck
controller built with the latest BiCMOS process for
optimum speed and efficiency. Both PWM channels
operate 180^o out of phase with each other to minimize
input capacitor ripple current and input noise. The
control loop has two stages of regulation. During steady
state to medium output disturbances, the loop operates
in fixed frequency, PWM mode while, during a large
voltage disturbance (~±6.5% nominal), the loop
becomes hysteretic; meaning that for a short period, the
switching MOSFETs are switched on continuously until
the output voltage returns to its nominal level. This
maximizes transient response for large load steps, while
operating nominally in fixed frequency PWM mode.
Voltage mode control is used to allow for maximum
flexibility and maintain good transient regulation. The
operating voltage range is 4.5V to 14.5V and the output
voltage can be set down to 0.7V. Start-up surges are
prevented using built in soft-start circuitry as well as
resistor-less current sensing for overload protection.
Other protection features include UVLO, dual level
enable thresholds, over voltage latch off protection,
power good signal and dual level over current protection.
Theory of Operation
The output voltage of the converter is sensed at the
inverting input of the error amplifier. This is connected to
V_OUT via the two feedback resistors. The non-inverting
input is connected to the internal 0.7V reference and the
two are compared to produce an error voltage. This error
voltage is then fed into the non-inverting input of the
PWM comparator and compared to the 1.5V voltage
ramp to create the PWM pulses. The PWM pulses
propagate through to the MOSFET drivers which drive
the external MOSFETs and create the power switching
waveform at the set DC (duty cycle). This is then filtered
by a power inductor and low ESR capacitor to produce
the output voltage where V_OUT ≈ DC×V_IN. As an example,
due to a load increase or an input voltage drop, the
output voltage will instantaneously drop. This will cause
August 2009
10
M9999-082809-A
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