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TPS40192 question for ENABLE function

Brian Wang0928
Genius 13410 points
Other Parts Discussed in Thread: TPS40192

Hi,

There is an question from customer side. The output voltage is not requlated normally when EN pin is tied to the external voltage 18V. In the D/S, the absolute max. voltage can be up to 20V. So it means that the voltage level should be ok with 18V. But we found that the output voltage goes down to 7.5V (Conditions: Vin=12V, Vout=9V for panel Half AVDD application)

PS: For power sequence design, to supply an external voltage to EN pin to make proper sequence for system requirement. 

Could you kindly let us know what happened on this IC when supply a 18V to EN pin?

In the D/S, it shows that the total current into the ENABLE pin is limited to no more than 500 uA. Why? If the current is great than 500uA, what happened?

 

 

This is urgent case for my major customer, pls kindly help to support this asap, Very thanks.

TI FAE

Brian Wang

 

 

 

 

 

  • 0
    TI__Guru 54780 points

    Brian,

     

    Forcing 18V on the EN pin from a low impedance source will likely result in damage to the IC.  The latest version of the datasheet specifically covers this:

     

    The shift in voltage that you are seeing is likely a result of ground current.  The Enable current generated by the 18V on EN must flow out of the ground of the TPS40192 controller.  The 16.7% drop in output voltage is a 98mV shift in the reference voltage.  In addition, the 1kOhm series resistance estimated does not maintain beyond 1mA of current, when a bi-polar in parallel with the 1k-ohm resistor will decrease this resistance as the current increases further.  The current generated by a 18V source could exceed the 17mA estimated by this model.

    If enable must be pulled up by an 18V source, a series resistance of at least 34kOhms should be used.