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Industrial Interface Forum

Pokkun
Genius 4695 points
Part Number: UCC21520

Hi members.

We are now proposing the following circuit at UCC 21520.

On top of that, I have a question about UCC 21520.

So, please teach me about below.

＜Question＞

①Can PowerA and PowerB share the same power supply?

(Assuming PowerA = PowerB = 24 V)

②When using this proposed circuit to generate PowerA and PowerB with separate power supply,

　do I have to connect a power supply with a capacity of 4 to 6 A to the VDDA / B terminal?

　(I ask you questions after checking the description below)

Could you help us?

Best Regards,

Masumi Sekiguchi

  • 0
    TI__Genius 9130 points
    Masumi-san,

    (1) If you connect PowerA to 24 V, this will be ok for the UCC21520 abs max rating on VDDA/B. However, the external FETs CSD18504 are limited to Vgs +/-20 V abs max - so the drive output would exceed the FET abs max rating. Since most FET's are limited to +/-20 Vgs max, I would recommend connecting VDDA/B to a bias supply ~12-16 V max. FET's with higher Vgs max rating are available, but they are not so common, the choice will be very limited.

    (2) The spec for Io peak source/sink current is not a steadt sate or DC requirement, it's the maximum peak charging or discharging current into/out of the the FET gate capacitance. This peak current will actually be supplied by the local decoupling caps which are conncted to the VDDA/B pins. As shown in the table above, they are assumed to be 10 uF value for the test conditions above. The external power supply only has to supply the DC or average load current to keep the VDD caps charged, which will be much lower than the 4/6 A peak ratings above. The bias power depends on the switching freq and the total gate charge of the external FET's.


    I hope this answers your question, if so please click the "verify answer" button.

    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Genius 4695 points
    Bernard-san,
    Thank you very much for the answer.

    In addition, please tell me more one question about (2).

    ＜Question＞
    That is, when considering generating PowerA from PowerB (24 V) power supply,
    I think that PowerA can use the voltage dropped by LDO from PowerB.

    Is the consider correct ?

    ※As I/O peak source / sink current was supposed to be 4/6 A peak,
    　I thought that LDO seems not to be able to using.
  • 0 in reply to Pokkun
    Genius 4695 points

    I deleted it because I posted a wrong thread by Sekiguchi.

  • 0 in reply to Pokkun
    TI__Genius 9130 points
    Masumi-san,

    Yes you can use an LDO to generate the VDD rails PowerA from PowerB. You need to ensure that the use large decoupling caps on the VDD pins, these supply the high peak drive currents, not the LDO.


    I don't understand your question in the most recent post. Maybe you posted this to wrong thread?


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Genius 4695 points
    Bernard-san,
    Thank you very much for the answer.

    ＞Yes you can use an LDO to generate the VDD rails PowerA from PowerB.
    ＞You need to ensure that the use large decoupling caps on the VDD pins, these supply the high peak drive currents, not the LDO.

    ⇒I was able to understand this content.
    　Thank you very much.

    ＞I don't understand your question in the most recent post.
    ＞Maybe you posted this to wrong thread?

    ⇒Sorry, that's right.
    　I post it on appropriate thread, after that I will delete it.


    Best Regards,
    Masumi Sekiguchi