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TMS320F28377D: ADC protection

Nour Elsayad
Prodigy 30 points
Part Number: TMS320F28377D

Hello everyone,

I'm using the TMS320F28377D microcontroller, and in my project I have current sensors and voltage sensors. Each sensor can output a voltage from 0 to 5V (depending on the measured parameter), however, I designed my project such that the maximum measured currents or voltages are associated with sensor output voltage less than 3.3V.

The problem is that I get transient overshoots (up to 4.5V) in the sensor output voltage ... I haven't interfaced the sensors to the microcontroller yet. Do I need to add a protection circuit to clamp these transient overshoots or the microcontroller has a built-in protection and won't be harmed by these overshoots?

Thanks,

Nour

  • 0
    TI__Guru 60865 points
    Hi Nour,

    You definitely need to worry about this, as an overshoot on the ADC input could damage the device.

    The best way to prevent damage would be to prevent the voltage from going out of range. The easiest way to do this would be to buffer the signal with an op-amp with 0 to VDDA voltage supplies; this will ensure the ADC input never exceeds VDDA or goes lower than VSSA.

    Another option would to be to depend on the device internal clamping diodes. If the input voltage goes 0.3V above VDDA or 0.3V below VSSA, the input diodes inside the device will start conducting current. If the total clamping current in/out of all device pins exceeds +/-20mA the device could be damaged. To control the amount of clamping current, you can add some series resistance to the ADC input (but note that this will slow down the input, probably requiring a longer S+H duration). You can also steer some clamping current through external clamping diodes by adding them to the pin input network.