MP2910 – 5V/12V SYNCHRONOUS BUCK PWM DC-DC AND LINEAR POWER CONTROLLER

MP2910 Rev. 1.0

www.MonolithicPower.com

10

12/14/2011

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2011 MPS. All Rights Reserved.

OPERATION

The MP2910 is a 5V/12V synchronous buck

PWM DC/DC and linear power controller. It

adopts voltage mode PWM control and includes

internal

soft-start,

frequency-compensation

networks, power good signaling with specific

sequence. The part is operated at fixed 300 kHz

frequency providing an optimum compromise

between efficiency, external component size, and

cost. The linear controller is implemented to drive

an external MOSFET for regulation and it's

adjustable by setting external resistors. An

adjustable over-current protection (OCP) is

proposed to monitor the voltage drop across the

buck PWM DC-DC controller.

VCC Under-Voltage Lockout (UVLO)

VCC

Under-voltage

lockout

(UVLO)

is

implemented to protect the chip from operating at

insufficient supply voltage. The MP2910 UVLO’s

rising threshold is about 4.1V with a hysteresis of

400mV. It’s not-latch protection.

Internal Soft-Start

The soft-start is employed to prevent the

converter output voltage from overshooting

during startup. When the chip starts, the internal

circuitry generates a soft-start voltage (SS)

ramping up from 0V. When it is lower than the

internal reference (REF), SS overrides REF so

the error amplifier uses SS as the reference. The

output voltage smoothly ramps up with the SS

voltage. When SS is higher than REF, REF

regains control. The circuit enters into steady

stage operation. The SS time’s typical value is

2.5ms.

Power Good Indicator

The PG pin is the open drain of a MOSFET, it

should be connected to supply power by a

resistor network. When the FB voltage reaches

90% of REF voltage, the PG pin is pulled high

after an about 4ms delay. When the FB voltage

drops to 80% of REF voltage, the PG pin will be

pulled low.

Internal Loop Compensation

MP2910 is a voltage mode buck controller with

internal loop compensation using a high gain

transconductance error amplifier as shown in

Figure 2.

Figure 2 — Compensation Loop with

Transconductance Error Amplifier

The pole and zero of the compensation network

are:

P

12

1

f=

2π×R C

Z

11

1

f=

2π×R C

MP2910

internal

compensation

network

parameters:

GM=0.2mS ,

1

1

C =2.5nF ,

2

C =5pF

OPS (Over Current Setting, VIN Power on

Reset and Shutdown) (Pin 13)

OCP (Over Current Setting)

to set the over current trip point. Connect an over

(Pin 14), then the over current trip point can be

estimated according to the following equation:

OCSET

OCSET

DS(ON)

38μAR

- 0.4V

I

R

of the low-side MOSFET



