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LM27762: About protection diode and output capacitor capacity

Kaji@PAN
Mastermind 7805 points
Part Number: LM27762

Hi,

I am a FAE of a distributor dealing with TI products.
I received two questions from customers about the LM27762 device.
Could you answer the following questions?

1. In the charge pump circuit, when the input voltage is applied for a short time at startup, but the inverter is not yet operated,
The output capacitor may be charged positively by the load. In such a case, the output voltage may not rise normally, so add a Schottky diode in parallel with the output.
I am thinking of adding a diode to the OUT- of the LM27762.
But my customer's diode VF is 0.35V.
Although the maximum rating of OUT- is not described in particular, is 0.35V VF acceptable?

2. The recommended value for the output capacitor is 2.2uF.
However, the load side needs to use 10uF.
Is it possible to use 10 uF as the output capacitance of the LM27762?
Best regards,
  • 0
    TI__Genius 14876 points

    Hi,

    1. As discussed here:

    https://e2e.ti.com/support/power-management/f/196/t/806026?tisearch=e2e-quicksearch&keymatch=LM27762

    It depends of your load specifications. Can you give more details about your load?

     

    2. As mentioned in the LDO output capacitor (8.2.2.5.4) topic, you would need to make sure that ESR of your 10uF output capacitor stays low. I guess you would use those 10uF cap on the positive and negative side. The regulation of the system could be slightly worse, then it will be up to you to define if the regulation is good enough for your load.

    Thank you.

    Best Regards,

    Dorian 

  • 0 in reply to Dorian Brillet de Cande
    Mastermind 7805 points
    Thank you for your reply.

    1. Load is assumed to be about 120mA on OUT- side. There is no waveform because it is in the process of making a circuit diagram.
    Why is there no mention of the maximum rating of OUT- in the data sheet?
    This makes customer judgment difficult.

    2. There is additional information about your circuit.
    Since three identical circuits are connected to the output side of the LM27762, a capacitor of about 30uF is actually connected.
    Change the question, but is there a limit on the maximum capacitance of the output capacitor?
    Also, I was advised to keep the ESR low, but what should I assume about the ESR value?
    Best regards,
  • 0 in reply to Kaji@PAN
    TI__Genius 14876 points

    Hello,

    In the absolute maximum ratings GND to VOUT is specified to be at 5.8V. 

    I recommend you order an EVM : http://www.ti.com/tool/LM27762EVM and try the 30uF output capacitor or else and see if the regulation can suit your load specification. I think it would be easier for you to evaluate your system this way.

    Thank you very much!

    Best Regards,

    Dorian