MP3221

–2.7A, 1.2MHZ, HIGH-EFFICIENCY STEP UP CONVERTER WITH INPUT DISCONNECT

MP3221 Rev. 1.0

www.MonolithicPower.com

10

9/23/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

The MP3221 uses a constant frequency, peak

current mode boost regulator architecture to

regulate voltage at the feedback pin.

The

operation

of

the

MP3221

can

be

understood by referring to the block diagram of

Figure 1. At the start of each oscillating cycle

the MOSFET is turned on through the control

circuitry. To prevent sub-harmonic oscillations

at duty cycles greater than 50%, a stabilizing

ramp is added to the output of the current

sense amplifier and the result is fed into the

negative input of the PWM comparator. When

this voltage equals the output voltage of the

error amplifier the power MOSFET is turned off.

The voltage at the output of the error amplifier

is

an

amplified

version

of

the difference

between the band gap reference voltage and

the feedback voltage. In this way the peak

current level keeps the output in regulation. If

the feedback voltage starts to drop, the output

of the error amplifier increases, which results in

more current flow through the power MOSFET,

thus increasing the power delivered to the

output.

Start-Up Sequence

When MP3221 is enabled, the FAULT pin

drives the external Fault Disconnection PMOS

to turn on slowly. After the FAULT pin voltage

drops to VIN -1.8V, parts works and checks all

fault condition, if they are all in function.

MP3221 will boost the output voltage to the

expect voltage controlled by the internal soft

start.

Protection Operation

MP3221 has short-circuit protection function by

turning off the external PMOS after parts

startup. When FB voltage drops to 150mV due

to the SCP occurs or any other factors, FAULT

pin voltage will pull up quickly by MP3221`s

internal logic. Then the PMOS will disconnect to

isolate input and output.

This function won’t act

also check other safety limits including UVLO

and OTP.

To prevent the battery from discharging, the

FAULT pin of MP3221 will drive and turn off the

battery when the part is in shut down mode. It

also can disconnect output from input while the

output is shorted to GND, thus help protect

battery and circuit.