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Original question:

TPS7B81-Q1: TPS7B8150QDGNRQ1 Schematic review

TPS7B81-Q1: TPS7B8150QDGNRQ1: Protection diode

Arun Kumar X
Prodigy 10 points
Part Number: TPS7B81-Q1

Hello Together,

We are using this part TPS7B8150QDGNRQ1 in our C-Sample phase with the below configuration.

UBD_VP_PI is the reverse voltage and transient protected automotive battery voltage.VDZ5_PERM is 5V which is present always even during the sleep mode.

Output (VDZ%_PERM) has very lighter load and hence to protect the OUT PIN during OFF scenario (If Input voltage discharges faster than output voltage), we have used a protection diode D3280. 

      1. Please let us know if we have body diode present inside the chip itself or not?

      2, Do we really need diode for this part?

Regards,

Arun.

Bosch.

  • 0
    TI__Mastermind 34365 points

    Hi Arun,

    This device does not have integrated reverse-current protection, so this diode will be necessary if there is a possibility of a reverse voltage. The device does have a body diode that will conduct when there is enough reverse voltage. 

    Regards,

    Nick

  • 0
    Prodigy 10 points

    Hello Nick,

    Thank you for the reply.

    We also have given series resistor of 47R with the input supply.. If there is an diode already available in the chip, then during fast discharge of input the diode conducts and the current will be limited by 47R resistor.

    Wrost case (During power supply interruptions, battery voltage will be short for a while multiple times) internal diode current will be (5-0.4)V/47R = ~100mA. Does this discharge current handled by the device?

    Do you think still an external diode is necessary even we have an internal diode and the resistor to limit the discharge current?

  • 0 in reply to Arun Kumar X
    TI__Mastermind 34365 points

    Hi Arun,

    The body diode is a parasitic diode that is not intended to be used to conduct any current. The 47ohm resistor at the input will limit the current upstream, but the reverse current through the device will be unlimited when the input falls below the output because the input capacitor will quickly charge to the output voltage. In general we advise limiting reverse current to 5% of the rated current of a given device (7.5mA for this device), but it is difficult to estimate the reverse current because of the non-linear I-V characteristics of the body diode. Hence, it is recommended to use an external diode to avoid this issue altogether. 

    Regards,

    Nick