LM3495EVAL: lm3495 eval

Hello John

Thank you for your answer.

I calculate the ILP with Vout = 3.8V and Vin =12V Fsw = 5,5E5Hz and Lout = 1E-6 and i got as result 5.19E-12 for ILP.

The average (load) current is the valley current plus one half ILp-p  , I don't understand what you mean in this part.

I want to limit my current at 8A and i use the Rilim formula to determine de Rilim that i need for 8A limitation

i have Rdson= 2.5E-3.

 i got as Rilim = 1.36E-2

What do you think ??

Thank you for your help.

Hello John,

i realize that with any resistance i put on Rilim there is no limitation of current.

I choose Vout = 4V  with a Vin = 12V and for the current limitation i want to 6A so i choose for Rilim = 1.06K but i realize that the current increase more than 8A

so i decided to put a Rilim = 500 ohm  it is the same.

do you have any idea of what can be the problem?

Best Regards,

Adjagbe

Adjagbe,

I need your inductor value and switching frequency to calculate it with Vin = 12 V and Vout = 4 V.

hello John

Fsw = 5,5E5Hz and Lout = 1E-6

best regards

Adjagbe,

I also need the low side FET RDSon.  The calculated p-p inductor current is 4.85 A.

John,

the rdson value that i use for my calculation are 3.4 mOhm

i took this value from the datasheet of the low side FET whuch reference is HAT2165H

Best regards,

Adjagbe

John,

i had the same result as you for tes resistance value but in my test i didn't see any limitation of current.

i checked on my oscilloscope the value of my current it was around 8A i don't know why.

i don't understand why the limitation i'm suppose to have i don't have it.

it is possible to have some new eval board to make another test maybe the eval board i'am using it's damage.

thank you for your help,

Best regards,

Adjagbe

Adjagbe,

I have ordered a board to check.  I will close this thread for now and re-open it after I receive the board.

Hello John,

Hope you are doing good.

I have just reconsidered my design and read thoroughly the datasheet and your blog about valley current detection and I think I got it wrong from the start, the datasheet has me confused especially this part for page 22:

CURRENT LIMIT

For this design, the trip point for the current limit circuitry should be below the peak current rating of the output inductor, which is 18A. To account for the tolerance of the internal current source, the change in the RDSON of the low-side FET, and to prevent excessive heating of the inductor, a target of 15A has been chosen. A 3.8A margin exists between the expected 11.2A peak current and the current limit threshold to allow for line and load transients. Following the equation from the Applications Information section the value used for RLIM should be 3.32 kΩ 1%.

In this part, the explanation goes as if we should take the maximum current (average output current + half of peak to peak current) as current limit. This is true when the controller operating in “peak current detection”.

Since the LM3495 performs Valley current detection, the current limit should be set at: Average output Current minus half of peak to peak Current. Am I right?

I have done some calculations (see attached file) and performing tests and it seems to corroborate. Can you take a look and see if my assumptions are wrong and misleading?

Thank you.

Buck Considerations LM3495.xlsx