Other Parts Discussed in Thread: LM61460, , LM76005
Hi TI,
I would like to use TPS5450DDAR as -12V/3.5A output.
Can help to review my schematic?
Thanks.
Best regards,
Syukri
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Hi Syukri,
I would double-check this again given that you are want a 24Vin|-12Vout|3.5A IBB conversion.
Using Equation 6 from this app note (https://www.ti.com/lit/an/snva856a/snva856a.pdf#page=7) assuming 85% efficiency and 20% inductor ripple current, the calculated Ipeak is around 5.9A which is very close to the 6A minimum current limit of the device.
You may want to pick a 6A rated device which will have a slightly higher minimum current limited and allow for a more robust design given your application power conversion.
Perhaps you can look into the LM61460?
Regards,
Jimmy
Hi Jimmy,
Thanks for your reply.
Understood the Ipeak is closed to the min current limit.
By the way, we have another application as well with output as below.
+12V/3.5
5V/3.5A
3.3V/5A
Is the equation for the Ipeak applicable for this TPS5450 output as well?
LM61460 seems good but it has too long LT since I need it urgently.
Thanks.
Best regards,
Syukri
Hi Syukri,
I don't see any issues operating with those conditions for conventional buck topology.
The TPS5450 is able to handle 5A continuous current.
Only when the convert is configured for IBB is when the peak current should be observed since the current in an IBB setup is different than the current in a normal conventional buck.
Regards,
Jimmy
Hi Jimmy,
Thanks a lot for explanation.
For -12V, if I could reduce the Ipeak to have more margin from the Current Limit, should it be OK?
and do we have Pspice simulation model to simulate TPS5450 IBB?
Best regards,
Syukri
Hi Syukri,
Yes that is correct, you would need to make sure that the calculated Ipeak in IBB topology is below the minimum high side current limit with some margin. I think a 6A rated device will be appropriate for this conversion.
Unfortunately the Pspice model does not have IBB feature.
Regards,
Jimmy
Hi Jimmy,
Thanks for your prompt response.
For Ipeak, how much margin should we consider?
and regarding the voltage stress, my nominal input is 24V.
With output -12V, VMAX will be 36V which is OK since it is under the absolute maximum rating.
Is my understanding is correct?
Best regards,
Syukri
Hi Syukri,
I think a good margin would be 10% from the minimum peak current limit would be a good start.
There should not be any issue with voltage stress since the voltage seen on the IC is within the recommended operating conditions of 36Vin.
Regards,
Jimmy
Hi Jimmy,
OK, noted with thanks.
by the way, do you have other recommendation for this application with higher VIN rating?
Best regards,
Syukri
Hi Syukri,
Perhaps you might also want to look into the LM76005 which is a 60V|5A device that would be suitable given the higher VIN rating.
Regards,
Jimmy