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TPS7A49 TPS7A30

Hirotsugu Kobayashi
Mastermind 9530 points
Other Parts Discussed in Thread: TPS7A47, TPS7A33, TPS7A49, TPS7A30

Hi, all.

TPS7A4901 and TPS7A3001 are used for the positive and negative voltage application
Even if a negative power supply is started first, does TPS7A4901 start with no problem?

When the negative voltage started first by TPS7A47 and TPS7A33 in the past, the problem that TPS7A47 doesn't start occurred, so I'd like to confirm whether the same problem doesn't form.

Best regards, 

Kobayashi

  • 0
    TI__Prodigy 215 points
    Hi Kobayashi,

    When using a dual rail setup, the output of the positive rail can be pulled below ground if the negative supply is started first. This could cause problems for positive output LDOs, since they aren’t designed to operate in those conditions. I would suggest powering up the TPS7A4901 first to avoid such an issue.

    Also please be aware the absolute minimum for the output voltage is -0.3V. Lower voltages will damage the device.

    Regards,
    Yuanhao
  • 0 in reply to Yuanhao Wang
    Mastermind 9530 points

    Hi, Yanhao-san,

    Thank you for your answer.

    When the positive side started first, and negative voltage output made a bias positive, is it no problem?

    Best Regards,

    Kobayashi

  • 0 in reply to Hirotsugu Kobayashi
    TI__Prodigy 215 points

    Hi Kobayashi-san,

    Both the TPS7A49 and the TPS7A30 are actually able to turn on as long as their output voltages remain within the specified absolute maximums and minimums. Attached are some scope shots. The outputs are at non-zero values at the beginning, but once Vin is high, the output also turns high (The pink is the output, the yellow is the input):

    If you require further assistance, could you provide more information regarding your circuit? 

    Regards, 

    Yuanhao

  • 0 in reply to Yuanhao Wang
    Mastermind 9530 points

    Yuanhao-san

    Thank you for your support.

    How was it tested? Is there a load?

    Could you test in the state with the plus or minus load?

    Our waveform is attached.

    The positive and negative voltage starts up the same time mostly.

    But ambient temperature is changed, positive doesn't start thoght the output isn't biased.

    Regards,

    Kobayashi

  • 0 in reply to Hirotsugu Kobayashi
    TI__Prodigy 215 points
    Hi Kobayashi-san,

    I tested the TPS7A49 by applying a bias voltage of -0.3V and a bias current of 10mA, and I tested the TPS7A30 by applying a bias voltage of 0.3V and a bias current of 10mA. A bias of 0.3V was selected as to not exceed the Absolute Maximum ratings of the device.

    These devices are designed, characterized, and tested for operation within the recommended operating conditions stated in the respective datasheet. Exposure beyond the recommended operating may result in performance and reliability degradation. As such care should be taken to design applications within the recommended operating conditions.

    Regards,
    Yuanhao