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UCC39002: Fail to load share for DC 20V output

wells
Intellectual 460 points
Part Number: UCC39002

Hi Expert,

I want to use UCC39002 to load share with two 20V outputs of  DCDC Regulators.  I reworked UCC39002 EVB according to figure 5 high voltage application.

The schematics we tested are attached.

The preset circuit goal is that the input voltage of DCDC is 27V and the voltage of shared load terminal is 20.06v. However, in the actual debugging process, the voltage at the output terminal is about 27V, not the 20.06v I set. At present, the voltage measured to VDD is 9.37v, the voltage of triode e is 8.33v, and the voltage of triode C is 27.90v. The voltage at CS + of IC chip is 1.093v, and the voltage at CS - is 2.497v. The test values provided here are from the test 01 circuit diagram. Please help check whether the test 01 circuit diagram is correct.

 At present, I have two questions to ask:

 Question 1: At present, I use test 01 and test 02 circuits for debugging. The output voltage is close to the input voltage. When the input voltage is 25V, the output voltage is also 25V, which is equivalent to that the current sharing chip does not adjust the voltage and current. Please help check whether the circuit diagrams of test 01 and test 02 are correct? Please correct.

Question 2: How to set CS +, CS -, radj and rsens in the circuit diagram in the high voltage circuit?

 

Thank you very much!

Test 02.pdfTest 01.pdf

  • 0
    TI__Mastermind 40520 points

    Hello wells,

    Thank you for your interest in he UCC39002 load-share controller.

    In both Test 01.pdf and Test 02.pdf schematics, the adjustment signal to the top of R11 should come from the collector of transistor Q1, NOT from the emitter. The way is connected now, the regulator is working with no feedback signal and that is why the 20V output is running at ~27V.

    After that, the high-side current-sense arrangement of Test01.pdf is not recommended. The divider strings of R9,R16 and R10,R17 are usually 1% resistor and can have an error of up to 4% on the current signal.  This signal which is ~2.5A in 10mR is only 25mV and represents about 0.1% of the output voltage, so the UCC39002 could actually be presented with a negative current signal. You would need dividers with 0.01% accuracy to overcome this issue.

    I recommend to use only the low-side current-sense arrangement of Test 02.pdf (and Figure 5) when working with the high-voltage implementation.

    Please read the datasheet thoroughly to understand the principles of current sharing and to adjust the circuit values to work within the requirements of the controller.
    For example, the gain of the current sense is required to be >3, yet your circuit shows a DC gain of 1. I also believe that the ADJ resistor R7 is too high in value.

    Finally, in the Test 02.pdf, the sense resistor R14 appears to be shorted out with GND symbols on both sides.  Please staudy the connections in figure 5 for the propoer way to connect R14 and the load-share circuit.  Be aware that the bottom end of R11 corresponds to SENS- and should be connected at the load.

    Regards,
    Ulrich 

  • +1 in reply to Ulrich Goerke
    Intellectual 460 points

    Hi Ulrich,

    Thanks for your kind help.

    According to your commments, I reworked the EVB. It worked well.

    Best Regards,

    Wells