EM5305VT datasheet(9/12 Pages) EXCELLIANCE

9 / 12 page

2013/7/11

A.2

EM5305

Functional Description

EM5305 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

The VCC pin provides the bias supply of EM5305

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

To let EM5305 start to operation, VCC voltage must

be higher than its POR voltage even when the

COMP/SD# voltage is pulled higher than enable

high voltage. Typical POR voltage is 4.05V.

Shutdown

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

disable EM5305. Pull down COMP/SD# pin below

0.4V can disable the controller.

Soft Start

EM5305 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)

OCSET

OCP

•

When OCP is triggered, EM5305 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, EM5305 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 60% VOFS.

When UVP is triggered, EM5305 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 130% VOFS.

When OVP is triggered, EM5305 will turn off upper

MOSFET and turn on lower MOSFET.

REFOUT and OFS

The REFOUT pin provides the 0.8V voltage output

with 5mA sourcing/sinking capability. The OFS pin

is high impedance input and receives a voltage

range from 0.4V to 3V as the reference voltage.

Connecting a resistor between REFOUT pin and

OFS pin can provide 0.8V as the reference input. By

sourcing or sinking OFS pin through the resistor can

adjust the input reference. Show as Fig.1

Source/sink

control

OFS

REFOUT

0.8V

Fig.1

REFOUT and OFS application.

EM5305VT Datasheet(PDF) 9 Page - Excelliance MOS Corp.

EM5305VT Datasheet(HTML) 9 Page - Excelliance MOS Corp.

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