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TMS320F28379D: Can it drive optocoupler based drivers having requirement of around 12 mA directly?

Sayandev Ghosh
Prodigy 250 points
Part Number: TMS320F28379D
Other Parts Discussed in Thread: UCC23513, TMDSDOCK28379D

Can a direct wire connection from epwm pin of F28379D experimenter kit is sufficient for the input forward current of gate driver UCC23513, which is around 12 mA, considering a resistance in series ?

Thanks in advance

Regards

Sayandev

  • 0
    TI__Guru* 95315 points

    Sayandev,

                  The max current a pin can source is provided in 8.6 Electrical Characteristics (page 57 of SPRS880O), which is 4 mA. This current is not sufficient for the forward current of the e-diode. UCC23513 datasheet clearly says the below (page 20):

    To turn the e-diode "ON", a forward current in the range of 7mA to 16mA should be driven into the Anode. This will drive the gate driver output High and turn on the power FET. Typically, MCU's are not capable of providing the required forward current. Hence a buffer has to be used between the MCU and the input stage of UCC23513 . Typical buffer power supplies are either 5V or 3.3V. A resistor is needed between the buffer and the input stage of the UCC23513 to limit the current. It is simple, but important to choose the right value of resistance. The resistor tolerance, buffer supply voltage tolerance and output impedance of the buffer, have to be considered in the resistor selection. This will ensure that the e-diode forward current stays within the recommended range of 7ma to 16mA.

  • 0 in reply to Hareesh Janakiraman
    Prodigy 250 points

    Thanks for the answer Hareesh sir. However I would like to ask if TMDSDOCK28379D have the same maximum current a pin can source?

    Secondly, in pg-49 of SPRS880O under absolute maximum ratings , 'Output Current - Digital output (per pin) ' is given as -20 mA to +20 mA. Can you please explain it ?

    Thanks in advance

    Sayandev

  • 0 in reply to Hareesh Janakiraman
    Prodigy 250 points

    I have been studying the document SPRS880O particularly, pg-57 that you referred to. There I found that sourcing current IOH is given as -4 mA 'minimum'. And from pg-49 of same document shows absolute rating of output current for digital output is 20 mA / pin. Thus, can it not be concluded that it can safely source 8mA - 10mA current for driving the e-diode?

  • 0 in reply to Sayandev Ghosh
    TI__Guru* 95315 points
    Sayandev Ghosh said:
    However I would like to ask if TMDSDOCK28379D have the same maximum current a pin can source?

    Yes. Think of the dock as a "break-out box" that provides a connection to all the GPIO signals. There is no buffering in the dock. 

    Sayandev Ghosh said:
    Secondly, in pg-49 of SPRS880O under absolute maximum ratings , 'Output Current - Digital output (per pin) ' is given as -20 mA to +20 mA. Can you please explain it ?

    I highly recommend you read the below post (and the posts it refers) carefully:

    https://e2e.ti.com/support/microcontrollers/c2000/f/c2000-microcontrollers-forum/747092/tms320f28075-questions-related-to-absolute-maximum-rating

  • +1 in reply to Sayandev Ghosh
    TI__Guru* 95315 points
    Sayandev Ghosh said:
    I have been studying the document SPRS880O particularly, pg-57 that you referred to. There I found that sourcing current IOH is given as -4 mA 'minimum'. And from pg-49 of same document shows absolute rating of output current for digital output is 20 mA / pin. Thus, can it not be concluded that it can safely source 8mA - 10mA current for driving the e-diode?

    I agree the “minimum” term can be a bit confusing. That number -4 mA has been put in the MIN column because it is negative. It should be read as “the GPIO pin cannot source more than 4 mA”, so that 4 mA number is actually the maximum. A “-“ sign is used because current is flowing out of the device (not into the device, in which case the minus sign is omitted). Also note that just because you can source up to 4 mA from a GPIO pin does not mean you can continuously draw 4 mA from all GPIO pins at the same time. 

    Absolute Maximum Ratings: The datasheet clearly says these are stress ratings. You should not operate the device under these conditions. Snippet from the DS:

    Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under Section 8.4 is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.