• Resolved

LMZ20501: EN Slow Ramp/Hysteresis

Part Number: LMZ20501

Hi Power Team,

Good afternoon, my customer is looking at using the LMZ20501 and we are interested to understand the EN better.

In this scenario, the EN input will be rising slowly (about 200uS/V), this will leave the device in between the VIL and VIH state for roughly 200uS. Will that be OK? The same will happen during turn-off, could this cause any issues?

With this, if there is any hysteresis built into the EN pin, that would be interesting to note as well. I realize it isn't in the datasheet/tested.

Thank you and please let me know if you have any questions.

Regards,

~John

  • Hi John,

    If the EN signal is clean, I think it should be OK.
    But anyway, I should have an EVM and could check the typical hysteresis on EN for you.

    Is EN tied to VIN or is VIN already high as the slow EN comes in?

    Regards,
    Denislav
  • In reply to Denislav Petkov:

    Hi Denislav,

    Thank you for taking a look at this! VIN will already be high.

    Regards,

    ~John

  • In reply to John Fedak:

    Hi John,

     

    I had a look on the EN behavior of the LMZ20501.

    First I looked at the rising and falling EN threshold with a very slow voltage ramp at the EN pin. The rising threshold is at about 865mV and the falling threshold at about 710mV.

    The built in hysteresis is therefore around 150mV.

    In a second measurement I applied square signal with a high slew rate. One can see that there is a delay between EN high and Vout high of about 125us.


     

    For the turnoff, there is not such a behavior.


     

    Additionally the device has a built in soft start of around 1ms. That’s why the output voltage does not jump instantly to 1.8V.

     

    After these measurements I applied a rising voltage ramp to the EN pin like in your application of 200us/V. The effective rising threshold is now ~1.5V and the falling threshold about 0.7V. Therefore you get a hysteresis of 0.8V. This result comes from the slow voltage ramp at the EN pin and the delay time when turning on. So the effective hysteresis depends on the applied voltage ramp at the EN pin.


     


     

    Hope this helps you for your application.

    Please don't hesitate to ask for further questions.

     

    Best regards,

    Michael