HB pin waveform is not true

8 posts / 0 new

Hi,everyone!

      Recently,Our team design a 400w led driver. My task is the LLC part. But,I have a problem.The LLC input voltage is 15v for D pin,12v for VCC pin. The HB pin waveform is not square wave,it's a straight line.I think it can not drive the MOSFET. I don't know why. And I also want to know how to test LCS708 is work properly.I need your help.Thank you.

첨부 파일Size
LLC part.pdf113.59 KB

D voltaeg of 15V is not high enough to start LCS. LCS OV/UV pin control the brown in and brown out behaviour. Refer to datasheet OV/UV pin section for more details.

D voltaeg of 15V is not high enough to start LCS. LCS OV/UV pin control the brown in and brown out behaviour. Refer to datasheet OV/UV pin section for more details.

I have change the register to meet the requirement of OV/UV pin, when I plugged into a power supply LCS708 was burned. What elements can burn this chip?

And this is my Schematic.12V for VCCPR,15v for B+.Thank you .

TitleSize
llc.pdf91.11 KB

From your shcematic, is there any reson you connect UV/OV pin to Vccp? UV/OV pin is supposed to be commected to B+ to sense the bus votlage through a resistor divider. You can refer to design example in our datasheet page 4 for an example schematic. Also when you power up the chip, double check if you apply the voltage on the right pin as your intention. otherwise applying high voltage on a low voltage rated pin may lead to faliure.

      I want to test this chip through a low voltage,so I have to forbidden OV/UV pin to make sure OV/UV pin's voltage satisfy the demand. When I test it from 10v for B+ to 37v for B+,it is OK. But when I increase the voltage to 38v,the HB pin's  wave form is wrong. After start up I see the square wave on the HB pin with 133 kHz,but it dissapears after 3 seconds. And I continue to increase the voltage , the HB pin have nothing.I can't find reason.

 

I see. To test out the chip using lower voltage, you can change the OV/UV divider ratio and allow the chip to start up with lower B+ voltage and proprotion to your desired level. is the operation coming back after certain time or it is operate once and never come back? Check if it is auto restart or not. if you have your spreadsheet, could you share with us so we have more information about your design.