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REF2030: Internal pulldown of VIN pin and the necessity of diode from VREF to VIN

Part Number: REF2030

1. VIN pin

The internal circuit of EN pin, pull-down or pull-up, is not seen in the datasheet. 

The external resister should be added if necessary ?

2. Diode from VREF to VIN

What happens when the input voltage is off (0V) after VREF goes up to 3V ?

Is a diode that VREF charge flows back to VIN necessary?

I will appreciate if anyone will answer.

Regards,

M. Ogawa

  • Hello,

    1. The datasheet does not specify the need for an external resistor on the EN pin. The pin should be pulled high or low and not left floating.

    2. There should be no path from the output to the input. I will get back to you if there are any bench results that say otherwise.

    Please let me know if you have any other questions.

    Thanks,

    Jackson

  • Thank you for the information.

    1. I'd like to know REF2030 has an internal pull-up or pull-down or nothing.

    2. VIN is min. VREF + 0.02 max. 5.5V in 7.3 Recommended Operating Conditions. So the path from output to input is necessary?

    Regards,

    Masa

  • Hi,

    1. The datasheet does not specify an internal pull up or pull down, but I can share with you my lab observations. If the device EN pin is pulled to ground, the device becomes disabled. If the EN pin is then disconnected from ground and left floating, the device is enabled again with the expected VREF value. By observing the behavior of a REF20 device, there appears to be an internal pull up. 

    2. I can look into this question, but I have some clarifying questions first: Is your question regarding reverse current protection? In this situation, what is the EN pin state?

    Thanks,

    Jackson

  • Hello, Jackson

    Thank you for the reply.

    1. I understood that EN pin has an internal pull-up in fact.

    2. EN pin is connected to VIN. VIN becomes below than VREF when power supply to VIN is stopped because VREF has a bigger capacitor than input-pin.

    Or the above situation will not occur because the input voltage decreases in the same way as the output voltage ?

    Regards,

    Masa

  • Hello,

    We cannot guarantee that the VIN of the REF2030 will remain at the same level as VREF once the supply voltage forced on the VIN pin goes to zero. I would expect in this situation, with a capacitor on VREF that is larger than the capacitor on VIN, that there would be a period of time where VREF is at a higher voltage than VIN. In this situation, I would expect that your explanation "VIN becomes below than VREF when power supply to VIN is stopped" is correct.

    Thanks,

    Jackson

  • I understood your explanation. Do you think it would be better to implement a diode that makes current path from VREF to VIN?

  • Putting a diode from VREF to VIN in the appropriate direction could be helpful, and if done correctly can be beneficial. I would expect it would be helpful to protect against reverse current for the REF2030.

  • OK. Thank you for your support.