2013/05/16

A.1

11

EM8564A

Protection

The EM8564A provides many protection functions

that intend to protect system from being damaged.

All the protection functions are listed as below:

Cycle-by-cycle current limit

The EM8564A has over-current

protection

thresholds. It is for cycle-by-cycle current limit,

which turns off MOSFET for the remainder of

the switching cycle when the sensing voltage of

MOSFET current reaches the threshold.

Over-load / Open-loop Protection (OLP)

When feedback loop is open, as shown in Fig. 18,

no current flows through the opto-coupler

transistor, the EM8564A pulls up the COMP pin

voltage to 5.2V.

When the COMP pin voltage is above 4.0V

longer than 56mS, OLP is triggered. This

protection is also triggered when the SMPS

output drops below the normal value longer

than 56mS due to the overload condition.

Fig. 18

Over Voltage Protection (OVP) on VCC

The

EM8564A

are

implemented

an

Over-Voltage-Protection

(OVP)

on

VCC.

Whenever the VCC voltage is high than the OVP

threshold voltage (29V), the output gate drive

will be shutdown to stop the switching of the

power MOSFET until the next UVLO (on).

The Over-Voltage-Protection on VCC function in

EM8564A is an auto-restart type protection. If

the OVP condition is not released, the VCC will

tripped the OVP level again and re-shutdown

the gate output. The VCC is working as a hiccup

mode as shown in Fig. 19. On the other hand, if

the OVP condition is removed, the VCC level will

go back to normal level and the output will

automatically return to the normal operation.

Fig. 19

Internal Over-Temperature Protection (OTP)

Internal 150

℃ comparator will provide over

temperature protection (OTP). OTP will not

shutdown system. It stops the system from

switching until the VCC is below the UVLO (off)

threshold voltage, the system will hiccup.

Gate out

VCC

t

t

UVLO(on)

UVLO(off)

OVP level

No Switch out