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MAX3232: Question about charge pump waveform

Satoshi
Guru 19655 points
Part Number: MAX3232


Customer measured two MAX3232's charge pump voltage, but one MAX3232 measured reverse polarity.

Is this waveform normal or abnormal?

※Probe polarity and the other condition (schematic, layout, BOM) are the same.

　2pin(V+) and 6pin(V-)  are both 6V and -5.6V.

Best regards,

Satoshi

  • 0
    TI__Mastermind 25705 points

    Satoshi-san,

    The waveforms from MAX3232 device 2 (right side) look normal to me. But the ones from device 1 don't. Generally depending on the load condition, the charge pump works periodically. If the output voltage (V+) is high enough (or low enough on V-), the charge pump stops charging. You can refer to this app note for more detail.

    e2e.ti.com/.../how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

    Can you swap device 1 and 2 between the boards to see if the behavior is related to the device itself. My wild guess is that somehow device 1's loading on the output is much heavier than that of device 2. You can also try multiple fresh devices in each test condition. Please let me know how the experiments go.

    Regards,

    Hao