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LM9061: LM9061 as a Charger OVP.

Ran Aloni
Expert 2365 points
Part Number: LM9061
Other Parts Discussed in Thread: BQ77905, , LM5060-Q1, LM5060

Hi all,

my requirement is to use an OVP circuit, to prevent from the customer to insert the wrong charger.

I was planning to use the LM9061 together with a battery pack (with BQ77905 chip set).

I know the battery has an OVP circuit, but the requirement is to prevent it from even "seeing" the battery.

I was expecting that the LM9061, connected as my schematics shows, will see that the voltage is higher than 25V, and won't drive the output.

instead it allows any voltage to drive Q14.

can you see why?

I thought that the ON/OFF pin should keep the output disconnected, until an input between 7V~23.5V is inserted, only then it will drive Q14.

when Q14 is open, the battery forces a voltage which is under between 15V to 21V - but that should happen only after the charger insertion and opening of Q14.

regards,

Ran Aloni

  • 0
    TI__Guru* 95801 points
    Hi Ran Aloni,

    I will check and get back to you on this.
    For battery OVP we recommend to use LM5060-Q1, which has programmable OVP pin to set the threshold accurately. What is your end system?

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Guru* 95801 points

    Hi Ran Aloni,

    Can you please provide test waveforms of marked nets to understand the issue.

    Thanks!

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Expert 2365 points

    Dear Rakesh,

    I attached a PDF with the scope plots.

    I made 2 experiment on the pins you requested.

    one with 21V which is the allowed voltage, and the second with 30V, which is way above the 24V OVP value.

    you can see a very similar reaction to the input voltage.

    also, before the experiment, I have changed the delay capacitor (C24) from 1uF to 0.022uF - it was a mistake.
    but couldn't see any effect.

    Ran30V Input.pdf

  • 0 in reply to Ran Aloni
    TI__Guru* 95801 points

    Hi Ran Aloni,

    Thanks for the test waveforms. But I did not see 30V input at PCHG+ in your experiment 2. Can you check ?

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Expert 2365 points

    Hi,

    I'm applying 30V, on the second experiment, but the battery regulates the voltage to be 21.2V.

    I would expect to see 30V on input and battery voltage on P+ ~20V.  But for some reason the Q14 opens right away and input voltage drops.

    Can you think of why?

    Ran

  • 0 in reply to Ran Aloni
    TI__Guru* 95801 points
    Hi Ran,

    Is diode D6 in place?
    Have you tested the circuit standalone ? i.e., without connecting to battery

    While applying 30V, What is the supply current limit set?

    Best Regards
    Rakesh
  • 0 in reply to Rakesh
    Expert 2365 points

    Dear Rakesh,

    I made an experiment without the batteries and results make sense now.

    changes are that D6 was shorted and delay capacitor is 0.1uF (for convenience reasons).

    in the last experiment we had D6 installed.

    I'll summarize:

    21V input - Q14 has opened with a 1ms delay.

    30V input - Q14 was opened for about 50ms and then closed.

    my conclusion is that in this delay of 50ms, the input voltage "meets" the battery voltage, which regulates it under 21V (even with the Diode D6).
    I can see in the datasheet that this delay is by design :

    this way, connection of a battery is not possible...

    1) is there any way to cancel this delay? for example connect the pin to 7.5V or VCC through a pull up?
    2) can I slow down Q14 for more than 1ms?
    3)is there a different chip I can use?

    Ran Aloni

    30V Input - no battery.pdf

  • 0 in reply to Ran Aloni
    TI__Guru* 95801 points
    Hi Ran Aloni,

    Correct. I suggest to use LM5060-Q1, which has programmable OVP pin to set the threshold accurately. The OVP delay time is 9.6us in LM5060-Q1

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    Expert 2365 points

    Dear Rakesh,

    few questions:

    1) can I use the LM5060 ? do I need the automotive version (-Q1) ?

    2) what is different here? do you think that the 9.6us, is not enough time for the battery to pull the voltage lower?

    3) maybe I should add a 10uF capacitor from PCHG+ to GND to slow down the change of voltage ?

    4) about LM9061 again, what will happen if I pull up the Delay Pin?

    Ran

  • 0 in reply to Ran Aloni
    TI__Guru* 95801 points
    Dear Ran,

    LM5060-Q1 is automotive version. We have single datasheet for both LM5060 and LM5060-Q1.
    If you see 50ms in LM9061 is causing problem, LM5060-Q1 acts fast - but again we need to verify on system level. Please provide your system block diagram showing the path of Charger, OVP protection circuit, BQ77905 chip, battery.
    As you know, if higher supply is connected to battery, the battery will clamp the supply voltage to battery level.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    Expert 2365 points
    many thanks, I will order the EVM and have a try.