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TPS62901: Use for 3V3: Is an external resistor avoidable set operating mode?

Julian Sandrock
Prodigy 20 points
Part Number: TPS62901
Other Parts Discussed in Thread: TPS62162,

I currently use the TPS62162 and I don't need any external resistor there to set the output voltage to 3V3.

When looking at the datasheet of the TPS62901 as an alternative part (due to bad availability of the 62162) it is not completely clear to me, wether or not this same configuration is possible.

It seems to me like I bascially have two options:

1) Connect MODE/S-CONF Pin directly to GND to activate AEE. In this case the output voltage is set with a voltage divider at the FB pin --> two external resistors needed

2) Alternatively I can leave the FB/VSET pin open to select 3V3 fixed voltage. But in this case I have to connect a resistor to the MODE pin to set the mode to fixed voltage operation, correct?

What would happen if I connect MODE to GND and leave the FB/VSET pin open? Is that an undefined operation mode?

Best regards

Julian

  • +1
    TI__Expert 3335 points

    Hi Julian,

    When you set MODE to LOW, it will enable the use of power save mode with AEE. When MODE is HIGH, it will be in forced PWM mode.

    You are correct that there are two options with the FB/VSET pin. Option 1 use an external resistor divider at FB pin. The device will sense the FB through the external divider network. Option 2 is to set the output voltage with a single resistor and the VOS is sensed through an internal resistor divider all according to the table 7-2 in the datasheet.

    The two pins are basically independent. If you connect MODE to LOW and leave FB/VSET open, it will have the target output voltage at 3.3V and have the device enabled to operate in Power save mode with AEE if needed. However, we recommend to use the 249K or larger resistor instead of leaving the pin open because noise can be injected into the pin if let open.

    MODE pin GND or HIGH only works with the external FB. If you would like to use VSET option, a resistor is required on the MODE pin.

    Hope this answers your question!

    Regards,

    Akshat

  • 0 in reply to Akshat Murali
    Prodigy 20 points

    Thank you, that explains the behaviour very good.

    I would suggest to take this explanation into account for the next revision of the datasheet. At least for me it was not obvious, that pulling MODE to LOW and leaving FB open would be a valid operating mode (because the datasheet says that MODE at GND means that the the voltage is controlled via external feedback).

  • 0 in reply to Julian Sandrock
    TI__Expert 3335 points

    Hi Julian,

    Yes, I apologize for the misunderstanding. Thank you for your input!

    Regards,

    Akshat