TMS320F280049: Input Clamp Current

Wilson Pang

Intellectual 590 points

Part Number: TMS320F280049

hi Sir,

May I know how does Input Clamp Current being calculated?

Is it by using the formula below?

Input Clamp Current = [External voltage - (3.3V+VF)] / Series resistance.

So if External Voltage = 12, Internal C2000 Clamp Diode VF = 0.7V, Series resistance = 10KOhm.

Then Input Clamp Current = [12-4] / 10000 = 800uA.

So 800uA < 2mA means it meets the C2000 specification.

Is this the right calculation? Thanks for your advice in advance.

over 5 years ago

0 Nima Eskandari over 5 years ago

TI__Guru 52080 points

Jason Whiles can you provide some knowledge as to how the internal of the GPIO would response to a 12V source connected to an input pin with a 10K resistor?

0 Jason Whiles over 5 years ago

TI__Expert 5950 points

Wilson,

The IBIS models for the device on the product page can be used to understand the turn on and on-resistance of the Power and Ground clamps. I'd suggest using those to understand the clamp characteristics.

The schematic you show would be a concern though. I would not recommend continuous current injection into the device at any level. There also could be supply sequencing issues if the 12V is present before the 3V3_MICRO.

I would recommend a level shifting buffer for this input or at minimum a resistor divider to VSS to keep the current external to the F280049.

Best regards,
Jason

0 Wilson Pang over 5 years ago in reply to Jason Whiles

Intellectual 590 points

Thanks for the info, Jason.

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TMS320F280049: Input Clamp Current