LP8860-Q1 with minimum external components

Di Wang

Hi,

I followed Figure 66 in the datasheet to design a solution with minimum external components. The 4 LED strings were not lit.

I measured, VLED+ was 30V, which 36.6V/360mA was suppose to be normal. OUT 1 to 4 were about 4V. FAULT was 5V high logic. EN was set 5V. The input frequency on PWM dimming pin was 200Hz.

It did not help,if I reset the NSS. Could you help check my SCH to find out why it was not lit?

Thanks.

over 9 years ago

0 Tomi Koskela over 9 years ago

TI__Genius 11020 points

Hello,

Which versio of the LP8860 do you have? There is A, B, C, D, E versions, which all have different EEPROM content. Most probably you have a version that is programmed to use register control for controlling brightness by default, not PWM input.

I don't see any obvious problem with the schematic. The inductor current rating looks quite low. Also make sure that there are good separate bypass capacitors on VDD and CPUMP. See also datasheet page 99 for details on the layout.

Thanks.

Best Regards,

Tomi Koskela

0 Di Wang over 9 years ago in reply to Tomi Koskela

Expert 1740 points

Thank you, Tomi.
Which version should I select?

0 Di Wang over 9 years ago in reply to Tomi Koskela

Expert 1740 points

Thank you, Tomi.
Which version should I select?

0 Di Wang over 9 years ago in reply to Tomi Koskela

Expert 1740 points

Thank you, Tomi.
Which version should I select?

0 Tomi Koskela over 9 years ago in reply to Di Wang

TI__Genius 11020 points

Hi,
B or D version has the brightness control mode set as PWM input duty cycle. See page 47 in datasheet for the default EEPROM settings in each version. Register address 0x66 two lowest bits define the brightness control mode, 00b = PWM input duty cycle. Note that there are other differences between versions as well, such as LED current, boost frequency etc.
Thanks.Best Regards,Tomi Koskela

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LP8860-Q1 with minimum external components