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Inquiry regarding GPIO embedded resistance on MSP430F5419

Atsushi Okui
Genius 4015 points
Other Parts Discussed in Thread: MSP430F5419

Dear all,

Now we are designing our board with MSP430F5419.

Then would like to know this embedded resistance on each GPIO.

I herewith describe this background.

[Hardware configuration]

Input signal to our board: 4-20mA and GND (2 wire), which are not isolated.

Input source is only 1ch.

H/W configuration in front of MSP430 GPIO: 4-20mA line is divided into GND by 100ohm resistance, which converts 4-20mA signal into 0~2V. Voltage follower OpAMP is placed on converted 0-2V signal.

In addition to above, we would like to add surge protection circuit for GPIO pin.

However, since I could not find any embedded hardware resistance information on GPIO, the suitable resistance value for this circuit is difficult to determine. 

We would like to ask you to disclose this internal hardware resistance information, or provide us your suggested 4-20mA input circuit diagram with surge protection in front of MSP430, in order to have further proceed.

We thank you in advance for your information.

Best regards,
  • 0
    Guru 46710 points

    Atsushi Okui said:
    Then would like to know this embedded resistance on each GPIO.

    You can ignore input resistance for your application because input leakage specified is 50 nA (nano Amps). Refer to "Leakage Current – General Purpose I/O" in device datasheet.

    Atsushi Okui said:
    which converts 4-20mA signal into 0~2V.

    I assume that you will sample input with ADC? Then why you ask GPIO, not ADC input properties? Anyway input leakage current for both, ADC and GPIO is identical.

    Protection: 3V surge supressor in parallel to 100ohm resistor. You shall check datasheet of surge supressor to be sure that it is linear in 0..2V input range. Anyway tests/measurements with/without supressor shall be made to check that it does not impact input signal. Between 100ohm+supressor and input pin I would put 330ohm series resistor.

    To be honest this is wrong place to ask about surge protection. You shall contact surge supression device manufacturer instead.

  • 0 in reply to Ilmars
    Genius 4015 points

    Hello, thank you for your prompt reply.

    I apologize but my post made you confused.

    As you mentioned, we would like to use embedded ADC on GPIO No.97 to sample the input signal.

    Simply, I would like to know about the maximum current level on GPIO.

    On page 39, the absolute maximum value for voltage level and diode current is  described as below;

    Voltage applied to any pin (excluding VCORE): –0.3 V to VCC + 0.3 V
    Diode current at any device pin: ±2 mA

    Please let me clarify whether these value are same as your recommended operating range for input voltage/current range on GPIO (No.97) of MSP430.

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    Guru 46710 points

    Atsushi Okui said:
    On page 39, the absolute maximum value for voltage level and diode current is  described as below;

    When input voltage does not go above VCC or below GND, then current does not flow through pin protection (clamping) diode(s). If your input can go outside GND..VCC range, then current-limiting resistor shall be added, to protect protection diodes from overcurrent (as I mentioned my approach to add 330ohm in my previous post).

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