［AP2152］

MS1348-E-00

14

2012/05

3) Protection Function

Protection

Description

Detection time

Shut-off state

Detection

condition

Release

condition

PGOOD

Thermal

When the IC temperature rises and reaches

the

detection

condition

and

exceeds

the

detection time, the DC/DC boost converter and

the LED constant current circuit are latched off.

*2

Latch off

125℃min

*1

ON

Over

current

Internal Nch power MOSFET drain current is

monitored by using an internal detection

resistor. If exceeding the detection condition,

the power MOSFET is turned off. And if

exceeding the detection time, the DC/DC boost

converter and the LED constant current circuit

are latched off.

*2

Latch off

2.6A

*1

ON

Over

voltage

(OVP)

If the OVP pin voltage reaches the detection

condition,

the

DC/DC

boost

converter

is

immediately shut off. In this case, the LED

constant current circuit is still operating

LED anode

voltage control

Auto-release

More than

1.2V

1.2V

or less

OFF

OVP pin

short

If the OVP pin reaches the detection condition

caused by the OVP pin shorted to GND, the LED

anode shorted to GND or the Schottky diode

open, the DC/DC boost converter and the LED

constant current circuit are immediately shut off

and the internal PGOOD FET is turned on. If the

OVP pin voltage reaches the release condition,

normal operation is resumed.

If exceeding the detection time, the DC/DC

boost converter and the LED constant current

circuit are latched off.

Cease all

Auto-release

↓

*2

Latch off

Lass than

0.1V

More than

0.1V

↓

*1

ON

UVLO

To prevent malfunction of the IC when the VIN

voltage reaches the detection condition. Circuits

excluding the UVLO circuit stop the operation. If

the VIN voltage returns to the release condition,

the IC resumes normal operation.

Cease all

Auto-release

3.75Vmin

4.45Vmax

ON

LDO

short

To prevent malfunction and over heating of the

IC when the VDC pin shorts to GND. The LDO

current is limited to low levels. If the short state

goes away, the IC resumes normal operation.

Cease all

Auto-release

More than

30mA

30mA

or less

OFF

CH

short

When the CH pin shorts to GND, the voltage

reaches the detection condition, and exceeds the

detection time, the DC/DC boost converter and

the LED constant current are ceased.

*2

Latch off

0.1V

*1

ON

LED

open

If the CH pin is opened due to an LED

disconnection or destruction as an open state,

the CH pin is latched off.

Internal timer

each CH

Latch off

Less than

LED set

current

when OVP

Voltage

*1

OFF

*3

LED

short

If the CH pin voltage reaches the detection

condition due to destruction by an LED short,

the CH pin is latched off.

Internal timer

each CH

Latch off

12V

*1

OFF

*4

ISET

short

To prevent heat generation due to increases in

the LED current when the ISET pin shorts to

GND, the Nch power MOSFET operation is

ceased. If the short state goes away, the IC

resumes the normal operation.

Cease Nch Power

MOSFET

Auto-release

ISET pin

GND

short

ISET pin

normal 1V

OFF

RT

short

To prevent heat generation due to increases in

the switching frequency when the RT pin shorts

to GND, the Nch power MOSFET operation is

ceased. If the short state goes away, the IC

resumes the normal operation.

Cease Nch Power

MOSFET

Auto-release

RT pin GND

short

RT pin

Normal 1V

OFF

Note:

*1. In order to release the latch off state, the PWM pin should be maintained at a low level for 50ms or longer or

the supply voltage should be pulled down less than the UVLO voltage.

*2. Set time by external capacitor on the TM pin. Refer to the timer latch setting.

*3. OFF when 1 CH or 2 CHs out of 3 CHs is/are open state, ON when all 3 CHs are open state.

*4. OFF when 1 CH or 2 CHs out of 3 CHs is/are short state, ON when all 3 CHs are short state.