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TPS61097 Adjustable Bypass Switching

sam ste
Prodigy 30 points

I am powering from a 3v battery and supplying to an msp430.

Would it be advantageous to turn boost on when msp430 is on or if the battery is nearing 1.8V, and shutdown/bypass when msp430 is in lpm4?

If so, how could this be accomplished?

Also, setting R1 and R2 to 200k with VIN=3.3, it would give 1.65V on EN line, half of VIN.

Referring to the data sheet, "If VIN is less than 1.3V then the bypass switch will be enabled. For VIN values above 1.50V (50% of VIH) the bypass switch is disabled."

Could you please explain how 1.3v and 1.5v was calculated, and how it is considered enabled/disabled?

Thanks.

  • 0
    TI__Guru**** 150950 points

    Yes, typically battery life is prolonged by turning off the boost for as long as possible and only turning it on when the batteries are too low or when a higher voltage is needed at the MSP430.

    Usually, a GPIO line drives the EN pin of the TPS61097, instead of your resistor divider.  If you do this, be sure and keep the voltage on the EN pin less than 1V above the input voltage.

    The 1.3V and 1.5V values refer to the example in that section with 200k resistors for R1 and R2.  This creates a voltage divider when activates the EN pin at half of Vin.  So, when Vin is 1.3V, EN is at 0.65V, turning it off.  When VIN is at 1.5V, EN is at 0.75V.  Vin would need to be just a little bit higher (1.56V) to meet the logic high threshold of 0.78V.

  • 0 in reply to Chris Glaser
    Prodigy 30 points

    Thanks, I better understand the example now.

    What I was trying to figure out was. If the msp has set EN low before entering lpm. It would continue to keep EN low even if the batteries are low.  How would I turn boost on when the batteries are low? Voltage supervisor?

    I had planned on on using the gpio anyway. Can I connect GPIO to EN directly?

  • 0 in reply to sam ste
    TI__Guru**** 150950 points

    Yes, you can usually connect the GPIO output to the EN input directly.  You will need to make sure that the logic levels of your GPIO are compliant with the EN pin threshold.

  • 0 in reply to Chris Glaser
    Prodigy 30 points

    Back to the battery question. Would an active high voltage supervisor  wired-or with msp430 and pull down resistor to enable pin work? 

  • 0 in reply to sam ste
    TI__Guru**** 150950 points

    Yes, I think that an SVS monitoring the input voltage could drive the EN pin high when Vin gets to some low level.  This would turn on the boost for low Vins.