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MAX3232: Request for schematic review of MAX3232

Grady Lee
Genius 4165 points
Part Number: MAX3232
Other Parts Discussed in Thread: TRSF3223E

Tool/software:

Hi, TI expert

When the customer connected MAX3232IPWR(TI) and MCU(STM32F446RETx) as shown below, the current consumption seems to be more than what is stated in the spec.

The customer wants to achieve less than 0.5W when power off.

Please review if there is an error in the schematic, and is there any expected cause of the problem?

Please check. Thank you.

  • 0
    Guru 316360 points

    The DIN1/DIN2 pins must not be left floating. Add pull-up resistors.

    Switching power supplies require careful layout. Please show your board layout.

  • 0
    TI__Guru 71910 points

    Hi Grady,

    As Clemens pointed out, the TTL input pins should not be floating. Incased current can occur when inputs are not properly biased.

    For lower power, you may need to move to a device that has the auto power down feature which will put the device into shutdown mode when the RIN pins float (not connected) to another enabled RS232 transceiver.

    -Bobby

  • 0 in reply to BOBBY
    Genius 4165 points

    Hi, Clemens, Bobby

    Thank you for response.

    1) Would it be okay to add 3.3V Pull-up resistors to DIN1/DIN2 as below?

    2) For lower power, you may need to move to a device that has the auto power down feature which will put the device into shutdown mode when the RIN pins float (not connected) to another enabled RS232 transceiver.

    → Can you recommend a part with auto power down function?

    3) I have attached the schematic and PCB layout. Please review them.

    Please check. Thank you.

  • +1 in reply to Grady Lee
    TI__Guru 71910 points
    Grady Lee said:
    1) Would it be okay to add 3.3V Pull-up resistors to DIN1/DIN2 as below?

    Yes.

    Grady Lee said:

    2) For lower power, you may need to move to a device that has the auto power down feature which will put the device into shutdown mode when the RIN pins float (not connected) to another enabled RS232 transceiver.

    → Can you recommend a part with auto power down function?

    If you need a 2T2R, you can take a look at TRSF3223E

    Grady Lee said:
    3) I have attached the schematic and PCB layout. Please review them.

    The RS232 schematic looks the same as when we originally checked it earlier. 

    I don't really see any issues on the PCB side of things.

    -Bobby