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TPS63001 EN pin as UVLO

Bojan Kosic
Prodigy 40 points
Other Parts Discussed in Thread: TPS63001

Hello,

Is it safe to connect EN pin of TPS63001 through a resistive divider from the input voltage in order to implement a rudimentary UVLO function, as shown in the schematics below? In other words, does the EN input tolerate voltages between GND and VINA?

We do understand that VIH and VIL absolute limits are not guaranteed but we need to increase the rising UVLO threshold of the VINA input somehow. We are in a position where we need to modify an existing design and this solution would be ideal for our needs.

Best regards,

Bojan Kosic

M.Sc.EE, Embedded Hardware Developer

Institute Mihailo Pupin

IMP-Telecommunications, Ltd.

Volgina 15, 11060 Belgrade, Serbia

  • 0
    TI__Expert 8420 points

    The EN tolerates voltages  between GND and VINA. As you can see in the datasheet of this device:

    The min voltage to be applied to enable the device and the maximum voltage where the device stays disabled is specified. Is this what you are looking for?

    I noticed that you re using the fixed version of this device the TPS63001. In this case R82 should be removed.

    What is the application? What are your operating conditions?

    What problem do you want to fix?

  • 0 in reply to Sabrina
    Prodigy 40 points

    Hello Sabrina,

    Thanks for the quick response. We just need a confirmation that the EN pin won't be damaged when it's not pulled to VINA or GND, but is set between VINA and GND. Judging by the given VIL and VIH, it seems that this is not a CMOS input, but rather some sort of TTL. Are we correct?

    We need an ad hoc solution for several already populated boards. The converter needs to start up only when input voltage is above 3.5V (100k - 51k divider produces 1.18V on EN when VIN is 3.5). We understand that VIL and VIH are not defined between 0.4 V and 1.2 V and it is not a problem if some boards start sooner than 3.5V. The only question is whether it's safe to have the EN input constantly at around 1.2V - 1.3V?

    Best regards,

    Bojan Kosic

    PS. R82 is not populated.

  • 0 in reply to Bojan Kosic
    TI__Expert 8420 points
    According to the datasheet , If EN pin voltage is equal to 1.2V and above, the device stays enables. I don't see any issue to keep the enable pin to 1.2V or 1.3V.
  • 0 in reply to Sabrina
    Prodigy 40 points
    Hi Sabrina,

    Thank you for your reply.
    Yes, we understand the datasheet but we're concerned with mode of operation not covered by the table.
    What will happen if we drive this pin with voltage between VIL and VIH?

    We did some measurements and found that EN switches state at approximately 800 mV.
    Is EN a typical digital logic input, or it has some internal reference and comparator?

    In our case, voltage on EN pin will be changing very slowly.
    Does EN input logic requires minimum input rise/fall time to reliably "switch" when input voltage is changing?

    Can we expect threshold voltage we measured (~800 mV) to change significantly with temperature and IC process variations?

    With resistive network on EN input we would like to prevent converter from starting if input voltage is below 3.4 V.
    We're doing that because we have Li-Ion battery and USB charger circuit at the input. When battery is deeply discharged and we connect USB charger DC/DC converter cannot start reliably due to high impedance/current limited source. By controlling EN voltage threshold we would like to make sure that converter starts when battery is charged enough (3.4 V) to support strong surge current.

    For our application it will be good if we can keep EN activating voltage between 3.3 V and 3.5 V (equivalently between 0.75 V and 0.85 V at EN input).

    Kind regards,
    Bojan Kosic
  • 0 in reply to Bojan Kosic
    TI__Expert 8420 points
    Thanks for the details,
    The 800mV could potentially vary with temperature and IC process variations. Unfortunately this is an old device, at that time , the functionality was checked through a go/no-go test, so there is no EN threshold level from production that can be provided.

    I don't think keeping the EN between 0. 75V and 0.85V is suitable solution for this issue. We can not guarantee those values, and I expect the device to not even get enabled at 0.75V.

    Is the "strong surge current" you mentioned cause by the inrush current of the TPS63001? In this case building an external soft stard ciruict with a diode and a capacitor may also be a solution.
  • 0 in reply to Sabrina
    Prodigy 40 points
    Thanks Sabrina for such detailed information!

    External soft start circuit could be a viable solution for our next hardware revision. We'll give it a try.

    The thing is that we're currently trying to solve the problem on a number of manufactured devices by reworking PCBs.
    That's why playing with EN threshold is still seems like a good idea to us.

    Can you please confirm if EN input is a digital CMOS, or a kind of voltage comparator with internal reference?

    We understand that you cannot provide any guarantee about EN voltage threshold or its variations. We can live with that in this situation.

    Best regards,
    Bojan
  • 0 in reply to Bojan Kosic
    TI__Expert 8420 points
    The EN input is a digital CMOS. As you measured, EN high level threshold is around 800mV. There may be devices that gets enabled at 750mV but it needs to be tested individually, but there may also be devices that get enabled at 850mV. As you need a work around for your application I would try to keep it higher than 850mV. Is it possible to achieve this by adjusting the resistive divider?

    Regarding the soft start circuit here is an app note (this can only be used with the adjustable version of this device)
    www.ti.com/.../getliterature.tsp