LM5176-Q1: LM5176 -constant current circuit - link to COMP

Aska Lee

Part Number: LM5176-Q1
Other Parts Discussed in Thread: LM5176

Hi TI expert:

Quesiton: While the simulated circuit refer the below circuit, the constant current can't be lower.

e.g The setpoint of constant current is 2.5A, but the simulated current is around 3.5A at 5A load. Evan it is setting lower (1A), it is also 3.5A.

The reason is there is a 0.25V Vf between Comp and op-Amp. So the comp voltage can't be pull down to 0V by op-AMP.

Do you have any idea?

Thanks.

Aska

over 5 years ago

0 Garrett Roecker over 5 years ago

TI__Mastermind 21720 points

Hello Aska Lee,

Thanks for reaching out with your question and for considering the LM5176 in your design.

The COMP voltage can be calculated using the Equation 7 and and equation 9 of the datasheet based on the application component selection. This will let you know if the diode drop is too large.

Please let me know if you have any questions.

Thanks,

Garrett

0 Aska Lee over 5 years ago in reply to Garrett Roecker

Intellectual 610 points

Hi TI expert:

Your answer is clear, but the equation is complex by multi parameter.

I tried many times by simulated mode and finally found it can work as picture. But I am looking for the optimal parameter.

Questions:

1) What value is the Acs?

2) Any suggest about Cslope? (e.g what is the suggest range that Cslope? Or what kind impact for buck mode and bukc-boost mode?)

Thanks.

Aska

0 Garrett Roecker over 5 years ago in reply to Aska Lee

TI__Mastermind 21720 points

Aska,

ACS is the gain of the current sense amplifier and is equal to 5V/V.

CSLOPE can be calculated using equation 26 of the datasheet.

Please let me know if you have any questions.

Thanks,

Garrett

0 Aska Lee over 5 years ago in reply to Garrett Roecker

Intellectual 610 points

Dear Garrett:

Thanks for your reply.

I keep tring the simulated modeling.

Aska

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LM5176-Q1: LM5176 -constant current circuit - link to COMP