LD6801GL datasheet(8/11 Pages) LEADTREND

8 / 11 page

LD6801

07/28/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD6801-DS-00 July 2016

Application Information

Basic Description

LD6801 is an external MOSFET controller for LED

lighting

current

ripple

eliminated.

The

REF

connection a filter capacitor to GND to suppressor the

100/120Hz LED current ripple. In the start-up process,

the LD6801 charges the REF capacitor quickly to avoid

LED voltage overshoot this time. And the device provide

adjustable short LED string protection, LED string open

protection and programmable over current limiting.

Theory of Operation

The LED light bar and LD6801 are both supplied by an

AC/DC current source. The drain of external MOSFET is

connected to the cathode of LED light bar. A sensing

resistor ROCP is connected between the source of

MOSFET and GND. The gate is connected to the OUT

pin of LD6801.

The LD6801 detects the OVP pin and OCP pin voltage

to adjust CREF Voltage and control the external MOSFET

operate in saturation region. When external MOSFET

working in the saturation region, the LED current ripple

transfer to LED voltage on MOSFET. If the drain Voltage

of external MOSFET break away saturation region, the

LED current ripple suppressor will invalid naturally.

Reference Voltage to LED Current Ratio

and LED Current Limit

There is K value ratio of the LED current and VREF

voltage. It provides stable voltage to let MOSFET be

working in saturation Region and suppress LED current

100~120Hz ripple. The following table is the K value

ratio setting.

RK parameter

(Ω)

K value ratio (VREF/VOCP)

< 1k

45~58k

> 75k

The over current protection is regulation the LED current

to limit threshold. The VREF operation voltage is limited

to 3V on REF pin. So that the LED limit current threshold

VOCP = ILED * ROCP = VREF / K

The suggestion for normal LED operation current is

0.4~0.8 times LED limit current threshold. It avoids the

larger LED current ripple to trigger over current limit

protection or produce MOSFET thermal issue.

LED String Open Protection

When OVP pin voltage and REF Voltage is under 0.2V.

The LD6801 would be go to LED open stage and OUT

pin and VREF voltage pull high until the LED string reply

connection.

LED string Short Protection

Fig. 11 is the function block of LED short protection. If

OVP pin voltage larger than 4V and in condition of IOVP >

40uA and continuous 150uS around, the LD6801 would

be turn off MOSFET until 40mS around. Then, the Over

voltage protection state is reset.

The programed over voltage protection calculated as

below:

VOVP_TH = 4V + (ROVP * 40A)

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