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Original question:

DCP021212D: Outputs higher voltage than spec.

DCP021212D: Implementing an application circuit

Jongkap Oh
Intellectual 320 points
Part Number: DCP021212D

Hi, 

There are some resistors in the datasheet page 17 of DCP02. (R1 ~ R8)

What is the purpose of these resistors?

Do I need to add this kind of resistors to application circuit?

I would like to get regulated voltage(22V) from LDO after DCP021212D which is configured to output 24V.

Thanks.

  • 0
    TI__Guru 50120 points
    Hi Jongkap,

    I believe those resistors you see between the respective positive and negative output and output side common is to illustrate the load resistors. For a 24V output isolated solution you would need to use the DCP021212D and connect your load circuit between the positive and negative output terminals of the isolated power module.

    Regards,
    Jimmy
  • 0 in reply to Jimmy Hua
    Intellectual 320 points

    Hi jimmy,

    I tested a circuit as below. (without load at VCC22V_ISO)

    Firstly, I tested this circuit without R77. 

    U34 stopped working soon and permanently. I think the cause was Max input voltage of U34 is 36V, but VCCRAW_ISO showed over 39V.

    And then, I inserted R77 and tested. 

    VCCRAW_ISO showed about 29V and U34 was working without trouble.

    Q1.  To suppress output of DCP02 like this is the purpose of the load resistor?

    Q2. Is 10k OK for load resistor? or is there any recommended value or equation for calculation?

    Q3. I will use circuit below in case that I need more current capability. Would you review this circuit?

    Q4. By the way, what is the correct output capacitor connection? If it is "2", COM could be left float?

    Q5. I would like to ask whether there is 'single chip' solution which outputs isolated and regulated 20 ~ 24V , up to 200mA and can replace my circuit.

    Thanks.

  • 0
    TI__Mastermind 28020 points

    Hi Jongkap,

    The resistors shown in the datasheet are load resistors required to apply a pre-load to the output.

    From the customer's schematic, have them replace R77 with a 2kohm to apply a load 10%.

  • 0 in reply to J Arrigo
    Intellectual 320 points
    Hi Jason,

    1. Would you let me know why the pre-load is needed for DCP02? I didn't see any comment about pre-load in the datasheet.

    2. It has to be 10%? It seems high to requie heat dissipation and large-sized resistor.

    3. Would you answer Q4 in my previous post? Figure11 of datasheet looks for DCP02--P(U) part, not for DCP02--DP(U)

    4. Would you answer Q5 in my previous post?

    Thanks.
  • 0 in reply to Jongkap Oh
    TI__Mastermind 28020 points

    Hi Jongkap,

    1. The pre-load is needed to meet the load regulation of the device.  This device is unregulated and does not have output side feedback to the controller.

    2. Yes, 10% load is needed to ensure the output voltage is not too high and meets the load regulation of the device.

    3. The correct output capacitor connection is device #1.

    4. No, we do not offer a single device solution for 4W.

  • 0 in reply to J Arrigo
    Intellectual 320 points
    Hi Jason,

    In my case, I will use an LDO, TPS7A4901 to get regulated output. Then, can it be possible to use smaller pre-load (such as 10k) if the output of DCP02 is below maximum input of the LDO?

    How about single device solution for 2W?

    Thanks.
  • 0 in reply to Jongkap Oh
    TI__Mastermind 28020 points

    Hi Jongkap,
    Any pre-load will help to bring down the output voltage more than No load. However, at 10% is the minimum where we spec our load regulation. Powering the TPS7A4901 from the DCP02 will draw some current, but additional load may be needed.
    The DCP021212D is capable of 2W.