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TPS22929D O/P powered while switch off or no i/p voltage- Implications?

Ashutosh Jain
Prodigy 60 points
Other Parts Discussed in Thread: TPS22929D

Hi,

We are using TPS22929D as a power switch.

Attached is the snapshot of the schematic for the power switching section.

 

This is the functionality:

1)       When VBAT is available  and there is no VUSB_5V, then the ON control for TPS22929 is high and VOUT= VBAT

2)       If both  VUSB_5V  and VBAT are available. Q5 NMOS would turn on, thereby disabling the TPS22929 and VOUT is disconnected from VIN.

  1. In this case VUSB_5V is directly connected to the output of TPS22929
  2. I have few questions regarding this: I read from datasheet that when TPS22929  is off, a 150 ohm load resistor will be enabled to bring down the o/p to 10% value. Since In this case, it will not be able to discharge the o/p ever, will it have any implication on the operation of this IC? Any damage on long term usage in this operation?

3)       In case VBAT is not available and VUSB_5V is available. VUSB_5V will be connected to the O/P while the switch is off. Do you expect any issues/anomalies in this case while VIN is 0 V but VOUT is 5 V?

 Thanks,

BR,
Ashutosh

  • 0
    TI__Genius 15740 points

    Hi Ahsutosh,

    1) That is correct.

    2) The internal output discharge resistance is meant to discharge the output down to 10% of its value.  If the output is held high, then the QOD resistance is dissipating a lot of power which might damage the device over time.  There are very similar parts available which do not come with this discharge resistance but still provide reverse current protection.  However, they are CSP devices.  What are the packaging limitations for this application?

    3) Because the ON pin is pulled low, the device should block reverse current effectively.

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Prodigy 60 points
    Hi Alek Kaknevicius:

    Thanks for your reply. Since we are dissipating almost 0.165 W on the internal resistor when the o/p is powered separately, Could you let us know if this power is enough to damage the device over time?

    Thanks,

    BR,
    Ashutosh
  • 0 in reply to Ashutosh Jain
    TI__Genius 15740 points

    Hi Ashutosh,

    Could you please provide the temperature range for this application as well as the expected lifetime for this device?

    Thanks,

    Alek Kaknevicius