LM3481: Schematic Review

Editing your title for the correct part no.

Hi John,

Thanks. Any update on the above queries?

Cheers.

I don't support that part.  Let me see if i can find someone to help.

Hi Florent,

The switching frequency is 300Khz
The value of C620 is 0.15uF
Please advise how to decide pin 3 COMP capacitor and resistor value.(C603,R603 and C620).

Below a much clearer schematic.

Thanks.

For choosing compensation components, you can refer to SNVA067C (AN-1286), using Rout=152kohm for the output impedance of the error amplifier:

Hi Florent,

Updated schematic below.

Currently this circuit with input 12V output can get 13.8V with 2.5A load.

But input 6V only can get  about 13.4V with 1.3A load. If increase the load more than 1.3A output voltage will slowly drop to about 8V.
Please let me know which pin or condition the capture waveform you need.

Thanks.

Hi Ikon,

With lower input voltage the peak current of the inductor is higher for the same output current. You will need to reduce the Rsense to 14ohm or below for the converter to be able to output 2.5A. 

Best Regards,

Florent

Dear Ambreesh,

After the change, the result isn't better.
1. Change R609 from 20m to 10m
2. Delete C620
3. Change C603 from 0.12uF t0 22nF
4. Change R603 from 1.3K to 6.8k

Vin 12V, output can’t remain voltage at 14V—Drop to 12V (load current  can’t get 2.5A)
Vin 6V, can’t get load current 2.5A, output voltage drop to 8V.

Please advise.

Thanks.

Dear Florent, Ambreesh,

Any update?

Customer want to achieve 6Vin and 4AIin with 14Vout and 2.5Aout. But is seeing Vout decreasing with increase in load.

Customer requirement is similar to PMP9491 reference design but also couldn't achieve what's stated in this reference.

Thanks.

Hi Florent,

Please refer attached file for the waveform requested.
The saturation inductance is 4.4A (will change to more higher value).
For the pattern design, followed the datasheet.

Cheers.

LM3841.xlsxLM3841.xlsx

Hi Perry,

Customer will keep their design for Booster circuit. (input 6-12V, output 14V, 2A).
Please advise whether the compensation circuit is alright in attached schematic.
For D608 will change to 8A , L608  will change to 6.8uH , 10A.

Thanks.

For the compensation, I would suggest you keep the changes that Ambreesh suggested earlier as well:

1. Change R609 from 20m to 10m
2. Delete C620
3. Change C603 from 0.12uF t0 22nF
4. Change R603 from 1.3K to 6.8k

Please take some oscilloscope shots of the switch node waveform, Isense, and COMP signals when this is done at the 5us/div timescale.  This will help us greatly in understanding the issues you are seeing.  

Perry

Hi Perry,

Please refer attached file for the waveform as requested and schematic.
Following your suggestion value for COMP pin, we can’t get output 14V.
Detail, please refer to attached file.

Thanks.

LM3841rev.xlsx

LM3481.pdf

Ikon,

Based on our testing and simulation, we believe that the circuit should work properly.  It is possible that the issue is with the particular design and due to an issue with the layout or other factors we cannot see from the schematic.  It might also help to send us the design files so we can look at the layout.

Is it possible to ship the board to us here in Santa Clara, CA

Perry

Hi Perry,

Customer is testing their custom board and the booster circuit is functioning properly.
But there is ome noise under no load and load.
After taking out the output E-cap C616,C617, C612,C613, noise become OK.
They try to change using Low ESR capacitor, the result is same as normal E-cap.
Is this what is also oberserved in your EVM (having this noise)?

Thanks.

Hi Perry,

Any feedback?

Thanks.

Dear Ambreesh,

Customer built limited prototype boards and therefore cant spare any.

Need your advise whether the switching frequency during no load is dependant on RFA.

Thanks.