LP8867C-Q1: LP8867C-Q1 Gain Margin Gap

Lawrence He

Expert 2800 points

Part Number: LP8867C-Q1

Hi, Support Team

We use calculator tool, what is mean Gain Margin Gap?

i didnt see datasheet about this infomation.

Gain Margin Gap

#DIV/0!

If gap > 3dB, external compensation is needed
If gap < 3dB, external compesnation is not needed

LP8867CQPWPRQ1_Design-Cal_V1p1.xlsx

if any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence

over 1 year ago

0 Gracie Guo over 1 year ago

TI__Genius 11766 points

Hi Lawrence,

DO you meet such problem?

It means the loop gain performance of boost.

BR, Gracie

0 Lawrence He over 1 year ago in reply to Gracie Guo

Expert 2800 points

Hi, Gracie

so PIN 9 is short to GND, gain margin gap i can igonor. is correct?

if any, Please advise me.

Thanks,

Best regards,

Lawrence

0 Gracie Guo over 1 year ago in reply to Lawrence He

TI__Genius 11766 points

Hi Lawrence,

I don't understand your question. Why is this related?

Gracie

0 Lawrence He over 1 year ago in reply to Gracie Guo

Expert 2800 points

Hi, Gracie

calculator tool is show Illegal, how to fine tune it.

8156.LP8867CQPWPRQ1_Design-Cal_V1p1.xlsx

V_{Boost_MAX}	26.29	V	Vboost_max should be at least 2V higher than VOUT_max
V_MINBOOST	8.10	V	Vboost_min should be lower than VOUT_Min
V_{BOOST_OVP_LOW (Initial)}	26.39	V	Must < 48V to avoid mistriggering SW_OVP
V_{BOOST_UVP}	24.08	V	Must > VLED_MAX to avoid mistriggering LED open

if any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence

0 Gracie Guo over 1 year ago in reply to Lawrence He

TI__Genius 11766 points

Hi Lawrence,

Pls see this LED forward voltage means Vf for one LED. The VOUT which is the Vboost required is too high for LP8867, so it's illegal. If you put in this value correctly, there should be no problem.

BR, Gracie

0 Lawrence He over 1 year ago in reply to Gracie Guo

Expert 2800 points

Hi, Gracie

okay. i will fine tune LED vf.

And about loop gain performance of boost= Gain Margin Gap

how to know gain margin gap actual; -9db~+3db?

if any, Please advise me.

Thanks,

Best regards,

Lawrence

0 Gracie Guo over 1 year ago in reply to Lawrence He

TI__Genius 11766 points

Hi Lawrence,

Do you mean you want to know the calculation process of loop margin?

You can unhide the sheet in the calculation tool to find this process.

BR, Gracie

0 Lawrence He over 1 year ago in reply to Gracie Guo

Expert 2800 points

Hi,Gracie

seen with FB Resistor divider relate. am i right?\

if any, Please advise me.

Thanks,

Best regards,

Lawrence

0 Gracie Guo over 1 year ago in reply to Lawrence He

TI__Genius 11766 points

Hi Lawrence,

Yes. It's from this FB compensation network.

BR, Gracie

0 Lawrence He over 1 year ago in reply to Gracie Guo

Expert 2800 points

Hi, Gracie

as below link, is also talk about FB compensation network?

(How to Measure the Loop Transfer Function of Power Supplies (Rev. A)) to understand how to measure loop transfer function.

if any, Please advise me.

Thnaks,

Best regards,

Lawrence

+1 Gracie Guo over 1 year ago in reply to Lawrence He

TI__Genius 11766 points

Hi Lawrence,

Right.

Power management

Power management forum

LP8867C-Q1: LP8867C-Q1 Gain Margin Gap