LMR62421: About setting of output voltage.

Hi Abe,

It is possible that the lower Vout is caused by the Vref deviation. Well, when the ambient temperature is around 25C, I think the deviation won't be so big. 

Here are some debug suggestion for your reference:

1. For the R1=10kohm, R2=110.4kohm, are they the actually measured resistances or the marked resistances?
2. How do you measure the Vout? For example, what equipment you used? And where is the test point?
3. Is the Vout stable? It's better to provide the Vout waveform for check.

Regards

Lei

Dear Lei san,

Thank you for your reply.

I answer your questions.

Q.
>For the R1=10kohm, R2=110.4kohm, are they the actually measured resistances or the marked resistances?

Ans.
That value is on the marked resistances.
However, I used accuracy of resistances are +/-1% and when I measured, it's kept the inside of +/-1%

Q.
>How do you measure the Vout? For example, what equipment you used? And where is the test point?

Ans.
I used eqipment was general voltage tester and test point was VOUT show on the data sheet.

Q.
>Is the Vout stable? It's better to provide the Vout waveform for check.

Ans.
I didn't have VOUT waveform picture but when I checked it by using the ociloscope, I couldn't be show strange wave of oscillation or confusion and so on.

I use coil value of 10uH now, is there a connection to the strange VOUT?

Best regurds,
Abe

Hi Abe san,

The inductor value you used should be OK. The feedback resistances and the setup look all good.

If you have more than one boards, could you take a AB swap experiment to check whether the lower Vout is linked to this specific device?

Regards

Lei

Dear Lei san,

Thank you for your fast reply.

I already swapped four pieces of deveice on the same board and cheked VOUT, but it result was same all thing.

Is it possible that VREF varies between VREF-min and VREF-max at 25℃ ?

By the way, I already used LMR62014 on the board, in stead of that I want to use LMR62421 because LMR62014 is EOL.
So I am trying to use LMR62421.
LMR62421 was no problem such as this.

If you have a recommend replacement parts, let me show please.
However it is notice that should be same package and pin assignment.

Best regards,
Abe

Hi Abe san,

abe yusuke said:

Is it possible that VREF varies between VREF-min and VREF-max at 25℃ ?

Generally, the VREF may varies between min and max within the whole temperature range. But it's very stable at one specific temperature. 

When you use LMR62014 on the same board, what's the Vout when there is no load?

Among the available devices, TLV61048 is recommended, but it's not p2p with LMR62014/LMR62421.

Regards

Lei

Dear Lei san,

Thank you for your reply.

I understood about connection between VREF and temprature you said.

>When you use LMR62014 on the same board, what's the Vout when there is no load?

When I was setting following, I can be show VOUT = 14.88V for actual value.

R1 = 10kohm
R2 = 110.051kohm
VOUT = 15.066V(->setting value)

I know that Vout is down if it put the loads.

Best regards,
Abe

P.S.
Sorry, it actual value is no load condition.

Dear Lei san,

>When I was setting following, I can be show VOUT = 14.88V for actual >value.
>
>R1 = 10kohm
>R2 = 110.051kohm
>VOUT = 15.066V(->setting value)

Sorry twice.
The above value is when I used LMR62421.
When I use LMR62014 it was shown below.

R1 = 13.3kohm
R2 = 150.051kohm
Vout = 15.11V(->actual value)
VREF = 1.23V

it actual value is no load condition.

Best regards,
Abe

Hi Abe san,

Could you take a photo of the top side of the four LMR62421 you used on which lower Vout was observed?

I'd like to check the top side markings of the four devices.

Regards

Lei

Dear Lei san,

Thank you for your reply.

I will try to take phots, hold on for a while please.

Best regard,
Abe

Dear Lei san,

Sorry to keep you waiting.

I send the photos of top and bottom side to you.
That is the same for four LMR62421.

Check it please.

Bestregard,
Abe

Hi Abe san,

Sorry based on the information so far, I didn't find the reasonable reasons that why the Vout is lower than expected. 

If necessary, could you ship several samples to me for further debug?

Regards

Lei

Dear Lei san,

Thank you for your reply every time.

Where can I send it if I want to do so ?

Best regards,
Abe

Hi Abe san,

Could you accept the E2E friend request I sent? After be E2E friends, I'll send the address by private message.

Regards

Lei

Dear Lei san,

I accepted your E2E friend request.

Best regards,
Abe

Hi Abe san,

I've sent the shipping address by E2E friend message.

Regards

Lei