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TMS570LS3137: TMS570LS3137 - Unused GPIOs

Alexander Spivak
Prodigy 10 points
Part Number: TMS570LS3137

Hello,

In spna173 (Reduction of Power Consumption)  Section 3.1 states that all unused GPIO pins should be configured as output and set to low level to avoid "floating voltage or shoot-through current" causing increase of power consumption.

1. Is this also applicable to all peripheral pins that can be set as GIO even if they are not powered up, or just for GPIO A and GPIO B pins?

2. If the default state of GPIO or GIO pins is input with pull down, why is it not enough to leave the unused pins at their default state after power up? Why would there be "floating voltage" if the input is pulled down by default?

Thanks,

Alex

  • 0
    TI__Guru**** 196776 points

    Hi Alex,

    Alexander Spivak said:
    1. Is this also applicable to all peripheral pins that can be set as GIO even if they are not powered up, or just for GPIO A and GPIO B pins?

    For all I/O pins that can be used as GIO pins. For example, Ball D3 (SPI2NENA/SPI2NCS[1]) can be used as either SPI2ENA or SPI2NCS[1] by configurating the pinmux, then configure D3 as GIO pin by programming the SPI2 SPIPC0 register.

    The pull-control and pull-type are determined by the value in SPIPC7 and SPIPC8. 

    Alexander Spivak said:
    2. If the default state of GPIO or GIO pins is input with pull down, why is it not enough to leave the unused pins at their default state after power up? Why would there be "floating voltage" if the input is pulled down by default?

    For the dedicated GIO pins (GIOA and GIOB), the default state is input and pull-down. If the input pin is floating, the voltage level of this pin is not fixed, sometime, it may be 0.5VCC, 0.3VCC. In this case, the device leakage occurs from external 0.5VCC (for example) to internal GND.

  • +1 in reply to QJ Wang
    Prodigy 10 points

    Hi QJ,

    Thank you for your reply. I'd like to follow up with some more examples/questions.

    1. For example, we are not using pin N17 (EMIF_nCS[0]/RTP_DATA[15]/N2HET2[7]). This pin is set to EMIF_nCS[0] in IOMM by default and its default state is high. Should we reprogram the IOMM to select N2HET2[7] that can be configured as GPIO and configure it as output driven low?

    2. Is the peripheral that turned off  (LIN for example) can be used as GPIO, or it needs to be turned on for that?

    3. If the peripheral needs to be turned on to set it to GPIO state, wouldn't it be consuming more power then if it just was turned off?

    Thanks,

    Alex

  • 0 in reply to Alexander Spivak
    TI__Guru**** 196776 points
    Alexander Spivak said:
    1. For example, we are not using pin N17 (EMIF_nCS[0]/RTP_DATA[15]/N2HET2[7]). This pin is set to EMIF_nCS[0] in IOMM by default and its default state is high. Should we reprogram the IOMM to select N2HET2[7] that can be configured as GPIO and configure it as output driven low?

    I think that leaving this CS pin as its default state is fine.

    Alexander Spivak said:
    2. Is the peripheral that turned off  (LIN for example) can be used as GPIO, or it needs to be turned on for that?

    If the SCI/LIN module is in reset, the SCI pins are internally pulled up. It is in GPIO mode, but it is not programmable to change the pull-type since the module is in reset. I don't suggest to turn the module on and reconfigure it.

    Alexander Spivak said:
    3. If the peripheral needs to be turned on to set it to GPIO state, wouldn't it be consuming more power then if it just was turned off?

    If the pin's default is input, and there is no internal pull, I will suggest add an external pull resistor