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Enable inputs of TPS62172

andreas.pfaeffli
Prodigy 20 points
Other Parts Discussed in Thread: TPS62172

I found an issue with the enable input stage on all my equipped boards.

The datasheet says:

VEN_H High Level Input Threshold Voltage (EN) min. is 0.9 V
VEN_L Low Level Input Threshold Voltage (EN) max. is 0.3 V

The equipped devices behave much more like:

VEN_H High Level Input Threshold Voltage (EN) min. is 0.6 V
VEN_L Low Level Input Threshold Voltage (EN) max. is 0.55 V

Is this an error in the datasheet or do we have a quality issue at this point?

  • 0
    TI__Guru**** 191445 points

    I am not 100% certain about TPS62172 specifically, but many devices have EN spec'd like a logic input with a guaranteed high voltage and guaranteed low voltage as shown in the TPS62172 datasheet.  In actuality the EN pin may show the characteristic you observe with a single threshold with about 50 mV hysteresis.  Many of the parts I directly support behave like this.  They technically meet the datasheet specification.

  • 0 in reply to JohnTucker
    Prodigy 20 points

    I with the spec from the datasheet I would expect a hysteresis of 600mV around a threshold of 0.6V. But what I get with my TPS62172 is a hysteresis of 50mV around the threshold of 0.6V. That's not what I expect to get, out of the spec. But if you tell me it's what I get with the chip, I need to apply a circuit which creates me an external hysteresis of 600mV in line with the enable input.

  • 0 in reply to andreas.pfaeffli
    TI__Guru**** 191445 points

    I had to edit my post.  It should be 50 mV hysteresis not 500 mV.  The spec says that EN is guaranteed to be high above 0.9V and guaranteed to be low below 0.3 V.  For that to be true, the actual high threshold must be less than 0.9 V (you measure 0.6V) and the actual low threshold must be above 0.3 V (you measure 0.55V).  I do not see a contradiction with that.  The hysteresis is internal.  You only need to pull EN high or low.