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TPS22965 backbiasing

Bertram Brummer
Intellectual 1906 points
Other Parts Discussed in Thread: TPS22965

my customer is using this device in multible sockets as a kind of or-ing function.  In his application the TPS22965 could be powered off with a high impedance load in Vin/Vbias (connected together).

Due to the or-ing architecture Vout  will see in his case 1.5 Volt  and with the body diode of the FET he is seeing a backbias voltage of 0.8 Volt at Vin/Vbias. I have received now the following questions:

* could this 1.5 Volt at Vout damage the device ?

* why is the low side FET not acive in this case? ( I guess this is due to a too low Vbias)

* could it happen that already the 0.8 Volt or a slightly higher voltage @ Vin/Vbias could activate the low side FET and therefore an oscillation could occure?

Thanks in advance

  • 0
    TI__Genius 15770 points

    Hi Bertram,

    To answer your questions:

    * The 1.5V at VOUT should not damage the device as long as the current through the device is not very high.

    * You are correct.  The low side FET (output discharge) is not active because VBIAS is not high enough to power on the device.

    * If the 1.5V on VOUT is a charge left on a capacitive load, then there is no risk for oscillation.  If 1.5V is being forced on VOUT then there may be a small risk for oscillation if a voltage as low as 0.8V is able to turn on the device (and low side FET).

     

    Regards,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    TI__Intellectual 1906 points
    Hi Alek,
    thanks for the quick response. Just got the info that Vin and Vbias are not connected during normal operation see 3.3 Volt @ Vin and 5.0 Volt on Vbias. When the power is switched off the 1.5 Volt at the Vout PIN are applied thru an external I2C Interface. Therefore no risk of oscillations.
    You say that the part will not get damaged only if the current is getting too high. I only can think about the current from Vout thru the diode to Vin could harm the device right? What's the max. current the diode can take ?
    Thanks and best regards, Bertram
  • 0 in reply to Bertram Brummer
    TI__Genius 15770 points

    Hi Bertram,

    You are correct, the reverse current through the device will travel across the diode from VOUT to VIN.  Because putting a reverse current through the TPS22965 is not a typical use case, we do not guarantee a maximum current across the diode.

    Do you have an idea of how much current the device will see in your application?

     

    Thanks,

    Alek Kaknevicius