LD8116C

05/05/2018

11

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD8116C-DS-00 May 2018

faster than 3 V/μs through 1.2V to 3.2V and continuous

8 cycles become into PWM dimming mode. If PWM

rising slew rate of DIM pin is larger than 3 V/μs, ICs will

reset cycles counter. Once into PWM dimming mode, it

will keep dimming mode until VCC is reset by UVLO_off.

Potentiometer Dimming

When DIM pin is connected a potentiometer to GND,

bias current source of DIM pin is pass thought this

potentiometer then cause a DC voltage potential on DIM

pin , LD8116C will transfer to PWM signal output on

OUT pin. The frequency of PWM signal on OUT pin is

1.5kHz around.

Internal Over Temperature Protection

When internal over temperature protection is occur

(135

C typ.). The OUT pin of LD8116C is open drain

and auto-recovery after thermal down to normal

operating temperature.

Optocupler Selection Guide

LD8116C converts an analog dimming signal into a

PWM waveform. In the majority of applications the

dimming signal needs to be isolated from the rest of the

application and an optocoupler is used to implement

either functional or reinforced isolation. Optocouplers

are an excellent choice since they are very cost effective

but nevertheless able to comply with virtually all safety

standards. The most common and cost effective

optocouplers are four-pin devices consisting of a LED

and a photosensitive BJT. With four pin devices only

collector and emitter of the BJT are connected to pins.

This limits device performance, especially switching

times, as will be discussed later. Six-pin devices having

the base of the BJT as well connected to a pin are seen

less often. With these six-pin devices bandwidth of the

transmission can be improved if necessary. Finally there

are high-speed digital couplers available that are

designed for very high data rates and offer a buffered

output with a nearly perfect PWM signal. While offering

superior

performance

high

speed

couplers

are

considerably more expensive than simple LED-BJT

couplers.

There are two parameters of an optocoupler that are

most important for use with LD8116C: the current

transfer ratio CTR and the switching times Tr and Tf.

A typical plot of Tr and Tf vs, RL taken from the data

sheet of a widely used 4-pin optocoupler.