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TLV61070A: Timing requirements for EN, VIN

Jim G
Intellectual 685 points
Part Number: TLV61070A
Other Parts Discussed in Thread: BQ24040

Tool/software:

I'd like to know what timing requirements exist for the EN and VIN inputs to TLV61070A.

I have a design where a 1S1P lithium cell (~3.7V) provides continuous input to the VIN pin, and EN is switched using a switch. To the left is a BQ24040 battery charger IC:

You can see I have about 44uF at Vin and 47uF at the output. My inductor is 3.3uH rated for Isat=2.5A, Irat=2.3A.

I do not have an external pulldown on EN as it's always connected to GND or 3.7V via the switch, but have tested with a pulldown applied as well.

The issue: If I have the battery connected and move the switch from OFF to ON, the TLV61070A appears to go into an unexpected state where 5V_EN or B+ (which are now connected via the switch) are shorted to GND.

However, if I have no battery connected and the switch is in the ON position when the battery is plugged in (or DC power supply is enabled), the TLV61070A starts up fine.

So to summarize what I'm seeing, if VIN is 3.7V and EN is switched from GND to (floating during contacts of switch moving) to 3.7V, the TLV61070A appears to short EN or B+ to GND.

But if EN and B+ come up at the same time with B+ and EN connected when the battery is plugged in, the IC functions properly.

What might be happening here?

  • 0
    TI__Expert 8605 points

    Hi Jim,

    There's no timing requirements for this IC. So please try catch waveform of B+, EN, BOOST_SW, 5V_BOOST_VOUT when the unexpected short condition happens. Trigger EN rising edge to catch the moment when EN switches up and device start up. I'll check what happened then.

    Best Regards,

    Travis

  • 0 in reply to Travis Wang
    Intellectual 685 points

    Hi Travis - thanks for your info.

    I actually believe I am tripping the OCP internal to my 1S1P battery due to the relatively short soft start time of the TLV61070A.

    The old boost IC I was using has a typical soft start time of 20ms, while the TLV61070A is 750us. I believe this results in higher inrush currents which trip the battery protection and shut the whole system down.

    I'll be searching for alternative boost IC solutions or potentially adding an explicit soft start circuit.