2014/03/21

preliminary

7

EM8822A

Switch Driver

The EM8822A contains a single totem-pole output

stage designed for direct drive of the power

MOSFET. The drive output is capable of typical rise

and fall time of 60ns with 1nF load.

Under voltage lockout

If the VDD voltage reaches UVLO(17V), the IC’s

internal blocks are enabled and start operation. If

the VCC voltage drops below 9.5V, most of the

internal blocks are disabled to reduce the operating

current. VDD voltage should reach UVLO(17V) again

to do restart up operation.

Constant current control

The output current IOUT can be represented by,

REF

out

CS

V

I

=

R

(2)

REF

V

：333mV

The pigure.15 show the Rcs location in Buck PFC

converter.

U1

EM8822

3

1

6

5

4

2

COMP

ZC D

VDD

GATE

CS

GN D

LED+

D1

LED-

+

C2

C5

L2

EE10 400uH

R2

R10

Q1

EMD02N60C TO-251

R cs

C1

Fig. 15

LED Open Protection

For LED lighting applications, when LEDs are opened,

the control loop tends to regulate rated current in

the converter. The VDD is connected to output

voltage directly. Under this condition, the output

output capacitor will be damage because of high

voltage.

EM8822A VDD pin has over voltage protection and

that voltage is 29V typical. When VDD reach 29V,

VDD down to UVLO(off) and restart up again. The

auto-recovery function can protect the output

capacitor avoid from damage.

LED Short Protection

For LED lighting applications, when a number of

LEDs in a string are shorted, the output voltage

drops. The VDD is connected to output voltage

directly. So VDD drops below UVLO(off) 9.5V and

the IC will cease operation.

Once EM8822A is shutdown, the rectified line

voltage will charge the VDD hold-up capacitor via

start-up resistor. This is same as start-up operation.

Thermal Shutdown

Thermal shutdown occurs when the IC experiences

a

junction

temperature

that

is

exceeds

approximately 140 degree C. It resumes normal

operation when the junction temperature drops to

or below approximately 110 degree C.

EM8822A