2013/04/22

Rev.A.5

9

EM5301

Functional Description

EM5301 is a voltage mode synchronous buck PWM

controller.

This

device

provides

complete

protection function such as over current protection,

under

voltage

protection

and

over

voltage

protection.

Supply Voltage

control circuit, as well as lower MOSFET’s gate and

the BOOT voltage for the upper MOSFET’s gate. A

minimum 0.1uF ceramic capacitor is recommended

to bypass the supply voltage.

Power ON Reset

be higher than its POR voltage even when REFIN

voltage is pulled higher than enable high voltage.

Typical POR voltage is 4.0V.

Shutdown

The COMP/SD pin can be used to enable or disable

EM5301. Pull down COMP/SD pin below 0.2V can

disable the controller.

Soft Start

EM5301 provides soft start function internally. The

FB voltage will track the internal soft start signal,

which ramps up from zero during soft start period.

OCP, Over Current Protection

The over current function protects the converter

from a shorted output by using lower MOSFET’s

on-resistance to monitor the current. The OCP level

can be calculated as the following equation:

DS(ON)

OCP

OCP

R

V

I

−

=

When OCP is triggered, EM5301 will shut down the

converter and cycles the soft start function in a

hiccup mode. If over current condition still exist

after 3 times of hiccup, EM5301 will shut down the

controller and latch.

UVP, Under Voltage Protection

The FB voltage is monitored for under voltage

protection. The UVP threshold is typical 0.6V.

When UVP is triggered, EM5301 will shut down the

converter and cycles the soft start function in a

hiccup mode.

OVP, Over Voltage Protection

The FB voltage is monitored for over voltage

protection. The OVP threshold is typical 1.04V.

When OVP is triggered, EM5301 will turn off upper

MOSFET and turn on lower MOSFET.

Feedback Compensation

Fig.1 shows the voltage mode control loop for a

synchronous-rectified

buck

converter.

The

compensation network consists of the error

The goal of the compensation network is to

provide a closed loop transfer function with

adequate phase margin.

OSC

Lo

Co

ESR

PHASE

DRIVER

PWM

COMPARATOR

REFERENCE

ERROR

AMP

DRIVER

REFERENCE

FB

COMP

C1

R2

C2

C3

R3

R1

Fig.1 Compensation for Voltage Mode Buck Converter