MP2212 – 16V, 3A, 600kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2212 Rev. 1.01

www.MonolithicPower.com

8

2/22/2012

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© 2012 MPS. All Rights Reserved.

FUNCTIONAL DESCRIPTION

PWM Control

The MP2212 is a constant frequency peak-

current-mode control PWM switching regulator.

Refer to the functional block diagram. The high

side N-Channel DMOS power switch turns on at

the beginning of each clock cycle. The current in

the inductor increases until the PWM current

comparator trips to turn off the high side DMOS

switch. The peak inductor current at which the

current comparator shuts off the high side power

switch is controlled by the COMP voltage at the

output

of

feedback

error

amplifier.

The

transconductance from the COMP voltage to the

output current is set at 11.25A/V.

This current-mode control greatly simplifies the

feedback compensation design by approximating

the switching converter as a single-pole system.

Only Type II compensation network is needed,

which is integrated into the MP2212. The internal

compensation in the MP2212 simplifies the

compensation

design,

minimizes

external

component counts. The loop bandwidth can be

adjusted by adding a feed-forward capacitor

which is in parallel with the feedback resistor from

output to FB pin.

Enable and Frequency Synchronization

(EN/SYNC PIN)

This is a dual function input pin. Forcing this pin

below 0.4V for longer than 4

part; forcing this pin above 1.6V for longer than

4µs turns on the part. Applying a 500kHz to 2MHz

clock signal to this pin also synchronizes the

internal oscillator frequency to the external clock.

When the external clock is used, the part turns on

after detecting the first few clocks regardless of

duty cycles. If any ON or OFF period of the clock

is longer than 4µs, the signal will be intercepted

as

an

enable

input

and

disables

the

synchronization. For automatic startup, connect

Soft-Start and Output Pre-Bias Startup

When the soft-start period starts, an internal

current source begins charging an internal soft-

start capacitor. During soft-start, the voltage on

the soft-start capacitor is connected to the non-

inverting input of the error amplifier. The soft-start

period lasts until the voltage on the soft-start

capacitor exceeds the reference voltage of 0.8V.

At this point the reference voltage takes over at

the non-inverting error amplifier input. The soft-

start time is internally set at 120µs. If the output of

the MP2212 is pre-biased to a certain voltage

during startup, the IC will disable the switching of

both high-side and low-side switches until the

voltage on the internal soft-start capacitor

exceeds the sensed output voltage at the FB pin.

Over Current Protection

The MP2212 offers cycle-to-cycle current limiting

for both high-side and low-side switches. The

high-side current limit is relatively constant

regardless of duty cycles. When the output is

shorted to ground, causing the output voltage to

drop below 50% of its nominal output, the IC is

shut down momentarily and begins discharging

the soft start capacitor. It will restart with a full

soft-start when the soft-start capacitor is fully

discharged. This hiccup process is repeated until

the fault is removed.

Bootstrap (BST PIN)

The gate driver for the high-side N-channel

DMOS power switch is supplied by a bootstrap

capacitor connected between the BS and SW pins.

When the low-side switch is on, the capacitor is

charged through an internal boost diode. When

the high-side switch is on and the low-side switch

turns off, the voltage on the bootstrap capacitor is

boosted above the input voltage and the internal

bootstrap diode prevents the capacitor from

discharging.

Input UVLO

Both VCC and IN pins have input UVLO detection.

Until both VCC and IN voltage exceed under

voltage lockout threshold, the parts remain in

shutdown condition. There are also under voltage

lockout hysesteres at both VCC and IN pins.

VCC Power Supply

control circuit and the gate drivers.

provided directly by a proper power rail or

circuit for VOUT=5V application.

It is noteworthy that the voltage applied on the