Questions regarding this power module

[FreshmanNewbie]

I'm seeing this power IC module - Link

I assume its a buck converter. In that case, on page 16 of the datasheet, Equation 4.1, There's this formula. Rvout = 8.2kohm * TRIM. If TRIM is 5, Then what would be the value of Rvout? Would it be

8.2kOhm5%= 0.41kOhm or 8.2kOhm5= 41kOhm. What happens when I like to increase more than 5 %?

Can someone please explain?

Also, there is increased ripple when 41kohm is used in series. Can someone also tell me how to reduce this.

 

[FvM]

Considering the requirement "Connect VOUT as close to the output capacitor", 0.41k seems the only reasonable assumption. The datasheet is rather unclear in this point.

Trim range is explicitely limited to 5% in the datasheet.

 

[KlausST]

Hi,

I agree with FvM.

If TRIM is 5

5 isn´t the same as 5%.

TRIM = 5 isn´t allowed at all. (But if you calaculate with 5 then the result would be 41k).

So use TRIM = 5% and get 0.41k.

Klaus

 

[FreshmanNewbie]

Hi,

I agree with FvM.

5 isn´t the same as 5%.

TRIM = 5 isn´t allowed at all. (But if you calaculate with 5 then the result would be 41k).

So use TRIM = 5% and get 0.41k.

Klaus

Thank you for your response. Can you tell me why TRIM can't be 5? 41k is not a valid resistor value that cannot be used? Can you please explain? And could you also tell me a way to reduce the ripple?

 

[KlausST]

Can you tell me why TRIM can't be 5?

Open the datasheet. Go to the place where the given equation is.
Look two lines above:

"This allows slightly higher out-put value programming, but should not exceed 5%
deviation from the VSEL selected value. "

It´s just meant for "fine tuning" ... as written in the same chapter.


Klaus

 

[FreshmanNewbie]

Cou

Open the datasheet. Go to the place where the given equation is.
Look two lines above:

"This allows slightly higher out-put value programming, but should not exceed 5%
deviation from the VSEL selected value. "

It´s just meant for "fine tuning" ... as written in the same chapter.


Klaus

Could you please provide an answer on the ripple?

 

[KlausST]

Hi,

Could you please provide an answer on the ripple?

Just keep on the datasheet information.

It´s makes no sense to complain about ripple in a situation this is off datasheet specification.
I guess it just becomes unstable with 41 kOhm .. that´s why they tell to just "fine tune" in the region of 5%.

Klaus

 

[FvM]

As stated before, the datasheet doesn't clearly specify trim resistor calculation. My conclusion that +5% trimming is achieved with 0.41k rather than 41k series resistor is substantiated by plausibility considerations not an exact datasheet specification. It could be verified by additional manufacturer info or empirically, not by additional guesses.

A series resistor of maximal 0.41k shouldn't pick up much noise (I guess that"s what you mean with "ripple"), but you may bypass the resistor with a parallel capacitor.