UCC256304: No use ACIN Wide range input DCDC converter

Hiroshi Doi35

Expert 2845 points

Part Number: UCC256304
Other Parts Discussed in Thread: UCC256303, UCC256302, LM5122

Hi Ben-san,

My customer want to use UCC256304 for Input DC90V-300V to output DC385V 200W isolated DCDC.

UCC256302 or UCC256303 does not meet such a wide range input by BLK voltage range.

How about the HV pin connection to kill the X cap discharge function?

Please propose the cct of Input DC90V-300V to HV pin cct.

over 5 years ago

0 Benjamin Lough over 5 years ago

TI__Mastermind 26215 points

Hi Doi-san,

It is not possible to use a DC input to HV pin of UCC256304. It is not possible to disable X cap discharge. The X cap discharge function will fail to detect a zero crossing and will attempt to discharge what it thinks is the X cap. This will lead to additional power loss and the IC package becoming hot.

I think it would make more sense to use UCC256302 or UCC256303 and use a circuit to clamp the maximum voltage on the BLK pin. This could be as simple as a zener diode connected into the BLK resistor string and gnd.

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Thank you Ben-san,

Do you mean kill the OVP function and make another OVP way such Rvcc to Vfb zenner Diode ?

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26215 points

Hi Doi-san,

The method I proposed would kill the input OVP function. Does your customer need this feature?

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Hi Ben-san,

May be Yes. But I think it is no problem. Choice another way.

DC50V to DC150V —-> no need efficiency.

DC150V to DC300V —> need High efficiency.

So I will recommend DC90V to DC300V input UCC256303.

For DC50V to DC90V add LM5122 boost controler before UCC256303.

I think the will use another aux. Flyback cct.

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26215 points

Hi Doi-san,

This seems reasonable to me.

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Hi Ben-san,

My customer corrected output voltage to DC50V.

Of course full wave S.R.

He asked me, both DC150V in and DC400V in, 97% maximum efficiency expected?

Can I say it depends on the design of the circuit such as a transformer?

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26215 points

Hi Doi-san,

Wider input voltage range tends to be more challenging for LLC. The wider input range forces you to operate over a wider switching frequency range. The further away from resonant frequency you operate, the less efficient the conversion will be. This is true for all LLC designs.

I think it is appropriate to say meeting the peak efficiency target will depend on the power stage design.

Best Regards,
Ben Lough

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UCC256304: No use ACIN Wide range input DCDC converter