TMS320LF2403A: input clamp protection

david goodin

IN the datasheet for the 2403, it says on page 71 that all inputs are protected with a clamp diode to up to 20mA. Does this apply to ALL inputs digital AND analog?

We have a 5k resistor in line with the A/D inputs and a client that wants to put 24 volts in to the board. Our input circuit would limit the current to about 3mA. Is that acceptable even if the input is 24 volts?

Thanks,

David

over 2 years ago

0 Hareesh Janakiraman over 2 years ago

TI__Guru* 95315 points

David,

I need to research this a bit. Will get back to you before Friday.

0 Hareesh Janakiraman over 2 years ago

TI__Guru* 95315 points

david goodin said:
Does this apply to ALL inputs digital AND analog?

Yes. However, 20mA is the maximum transient current that they can handle. It is not recommended to continuously run in a mode where this pin is clamped. Long term effects have not been studied.

david goodin said:
Is that acceptable even if the input is 24 volts?

Note that ADC input must be between 0v and 3.3v. It is not just the current, the voltage presented at the ADC input is also important. You also need to worry about the impedance of the source driving the ADC inputs. Too high an impedance may warrant a long acquisition time. You may want to consider a R divider to scale this thing down and then buffer the signal with a unity-gain OP-AMP circuit to lower the source impedance.

0 david goodin over 2 years ago in reply to Hareesh Janakiraman

Intellectual 410 points

Thank you for the quick response.

David

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TMS320LF2403A: input clamp protection