LP8861 Phase margin/Gain margin

kura

Genius 4680 points

Our customer would like to check LP8861 Phase margin/Gain margin using with LP8861-Q1EVM.

LP8861-Q1EVM http://www.ti.com/lit/ug/snvu456/snvu456.pdf

Could you please let us know resistor insertion point on EVM.

over 7 years ago

0 Sung Ho Yoon over 7 years ago

TI__Expert 4565 points

Hi,

You can add 20ohm(or so) resistor between boost output and upper FB resistor as shown here.

There is no pad for this, so you will need to lift up R12(upper FB resistor) to add this resistor.

Hope this helps,

0 kura over 7 years ago in reply to Sung Ho Yoon

Genius 4680 points

Sung Ho Yoon-san

Thank you for your reply.

Customer has additional request.

Could you please send actual Phase margin/Gain margin plot of LP8861 EVM to us,if you have.

Regards,

0 Liaqat Khan over 7 years ago in reply to kura

TI__Mastermind 18550 points

Hi,

Can you please give me the application conditions like Vin, boost output voltage (number of LEDs/string, LED Vf), current per string and boost switching frequency. Once I have these application conditions, I will measure stability margin and provide the plots.

Thannk you.

Liaqat

0 kura over 7 years ago in reply to Liaqat Khan

Genius 4680 points

Liaqat-san
Thank you for your reply.

Please use EVM default and LED configuration is 7S3P,Vin:13.2V.

regards,

0 Liaqat Khan over 7 years ago in reply to kura

TI__Mastermind 18550 points

Hi Kurahara-san,

Under these conditions, measured phase margin is 66.4 degree, gain margin is -18.53dB and cross over frequency is 5.33KHz.

I sent you a plot of this measurement via separate e-mail.

Regards,

Liaqat

0 kura over 7 years ago in reply to Liaqat Khan

Genius 4680 points

Liaqat-san

Thanks,I could receive a plot.

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LP8861 Phase margin/Gain margin