• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 2651 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MAX3232: Charge pump frequency

K.Hamamoto
Guru 12155 points
Part Number: MAX3232

Hi

I would like to know how much is the frequency of the internal charge pump.

Our customer found unknown current spike on the input current of 3.3V supply(VCC) with a fixed period which is 270us.

Do you think that is caused by the internal charge pump?

Regards,

Koji Hamamoto

  • 0
    TI__Mastermind 25705 points

    Koji,

    The internal charge pump is pretty fast. However it's the regulation loop that governs the TX output periodic amplitude variation, which is related to c1~c4 capacitor and TX output load (resistance and capacitance). Can you check if the supply current spike is correlated to TX output voltage ripple?

    Regards,

  • 0 in reply to Hao L
    Guru 12155 points
    Hi Hao,

    Thank you for your reply.
    OK. I will ask them to check the output of TX.
    I will feedback to you as soon as I get the update.

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    Guru 12155 points
    Hi Hao,

    They checked the relation of TX and the supply current spike. It was related to the TX and the spike.
    Why this spike is happen ? And how can they reduce this spike?

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Mastermind 25705 points

    Koji,

    MAX3232 has an internal charge pump to provide the voltage of TX. This voltage is also monitored and regulated to keep it within the spec - larger than 5V and less than abs max 7V. The mechanism is feedback. If the TX output is too low, the charge pump starts working. If the TX output is too high, the charge pump stops. Therefore you see the TX output has ripples and supple current has spikes. If you want to reduce the spike, you may try to add more cap on TX output pin to make the node is harder to charge/discharge. Please let me know if you have any questions.

    Regards,

  • 0 in reply to Hao L
    Guru 12155 points
    Hi Hao,

    The customer added the capacitor(1uF) to the output of TX. However the spikes(80mApeak) of supply current is not reduced.

    Is there any way to reduce the spike?



    Regards,

    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Mastermind 25705 points

    Koji,

    What cap valuex did the customer use for C1-C4? I assume they're 0.1uF since the supply is 3.3V.

    Maybe you can try use another option, C1=0.1uF and C2, C3, C4=0.47uF. By doing this, the output voltage ripple will be smaller. It might help current spike as well. Please let me know if it woud work.

    Regards,

    Hao