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OMAP-L138: VOH isn't high enough

Kien
Expert 3770 points
Part Number: OMAP-L138

Hi Champs,

According to the datasheet, IOH can source up to 6mA. And VOH is 2.4V min.

However, when customer connect the output pin (E4) to a pull down resistor (10K Ohm) then the VOH can only go up to 1.2V.

May I know if that's normal or not? And why?


Regards,

Kien Nguyen

  • 0
    TI__Guru**** 166599 points

    Hello Kien Nguyen,

    Thank you for the query.

    I will need more information regarding the GPIO output that you are measuring.

    Could you remove the pulldown resistor and measure the voltage. 

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    TI__Expert 3770 points

    Hi Sreenivasa,

    Thanks for your reply. The application is as below.

    They measured voltage on pin E4 at point A, voltage level is 3.3V at high state and 210mv at low state in pink color. So it is within the VOH range in the datasheet.

    Then they removed the resistor R305 and connected the Signal ST_LED0_L to a 10K resistor, the waveform now shows that VOH is only 1.2V and the VOL is 30mV. The question is: why VOH is only 1.2V in this case? Is there any pin configuration that makes this happen?

    Regards,

    Kien Nguyen

  • 0 in reply to Kien
    TI__Guru**** 166599 points

    Hello Kien Nguyen,

    Thank you for the inputs.

    Can you help me understand the use case for pulling the output low through the resistor?

    Can you please verify if the internal pullup is enabled. Can you reduce the 10K pulldown to 1K and do a test.

    Please refer below section in the datasheet.

    4.3 Pullup/Pulldown Resistors

    Tips for choosing an external pullup/pulldown resistor:

    Regards,

    Sreenivasa