MP3910 –PEAK CURRENT MODE BOOST CONTROLLER

MP3910 Rev. 1.11

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13

11/6/2014

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pin to 3.6V source with 14.4kΩ resistor, the

feedback signal can be connected to COMP pin

directly. If the detection voltage is lower than

185mV, MP3910 will enable the internal error

amplifier but turn off the pull up resistor. Then

COMP pin is just one output pin of error

amplifier and the feedback signal should be

connected to FB pin.

GATE

Start up

50µs

+

-

0.185V

55µA

High / Low

 

Figure 2: Feedback Mode Setting

Generally, it is recommended to place one

resistor with 5Kohm~10Kohm between ISENSE

pin and current sense resistor for the feedback

mode through directly COMP pin, and connect

ISENSE pin to current sense resistor directly for

feedback mode through FB pin.

Soft-Start

MP3910 uses one external capacitor on SS pin

to control COMP voltage rising for soft-start.

When the chip starts, the capacitor on SS pin is

charged by one 54uA current source at a slow

pace set by the capacitance. When the SS

voltage is lower than the external COMP

voltage, SS overrides the COMP signal so the

PWM comparator uses SS instead of COMP as

the PWM turn off reference. When SS is higher

than COMP voltage, COMP gains the control

back and the soft start finishes. The soft-start

can reduce voltage stresses and surge currents

during start up, also prevent the converter

output voltage from overshooting during startup.

Soft start occurs during the start up time and

protection recovery time after OLP, SCP and

OVP. During normal condition, the SS voltage

is clamped at 3.65V.

Programmable Oscillator

The MP3910 oscillating frequency is set by an

external resistor from the RT pin to ground. The

3

2.35 10





T

SW

R

f

The frequency setting resistor value shouldn’t

be too large for noise immunity consideration. It

is recommended to set the frequency within

30kHz to 400kHz.

Enable/SYNC Control

EN/SYNC is a digital control pin that turns

MP3910 on and off. Drive EN high to turn on

the controller; drive it low to turn it off. An

internal 1MΩ resistor from EN/SYNC to GND

allows EN/SYNC to be floated to shut down the

chip.

For external clock synchronization, connect a

clock with a frequency higher than RT set

frequency and between 80kHz to 400kHz, the

internal clock rising edge will synchronize with

the external clock rising edge. Select an

external clock pulse signal with low level width

less than 10μs, or else MP3910 may treat it as

EN power off.

EN/SYNC pin can not be connected to voltage

higher than 6V, when voltage source is higher

than 6V, a pull up resistor is recommend. For

resistor pull up condition, an internal zener

diode clamps the voltage at EN/SYNC pin. The

maximum pull-up current for the internal clamp

zener (assuming clamped at 6V) should be less

than 0.4mA. Typically 100k pull up resistor is

recommended. There is no problem if the clamp

voltage is distributed at higher than 6V if pull up

current is less than 0.4mA.

Current Sense and Over Current Protection

The MP3910 is peak current mode controller.

The current through the external FET can be

sensed through a sensing resistor used in

series with the source terminal of FET. The

sensed voltage on ISENSE pin is then amplified

and fed to the high speed current comparator

for the current mode control purpose. The

current comparator takes this sensed voltage

(plus slope compensation) as one of its inputs,

then compares the power switch current with

the COMP voltage. When the amplified current