• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 2 answers
  • Subscribers 15 subscribers
  • Views 353 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISO7842: Capacitive load

Zeev Guzman
Prodigy 10 points
Part Number: ISO7842
Other Parts Discussed in Thread: ISO7840

Tool/software:

 Hello,

according to the datasheet, the maximum allowed value of the output current of ISO7842 is 15 mA. Is it allowed to connect an RC circuit consisting of serially connected R = 33.3 Ω and C = 300 nF between OUT and GND of ISO7842 as shown in the diagram below?

The frequency of the input pulses is no more than 50 Hz.

If no, what are the maximum allowed capacitance and minimum allowed resistance in such circuit?

The similar question is about ISO7840. Parameters of the RC circuit connected between OUT and GND of ISO7840 are: R = 100 Ω, C = 1 nF. Frequency is no more than 1 kHz.

Thanks in advance,

Zeev

  • 0
    Guru 317480 points

    The capacitor initially looks like a short. The resistor must be large enough to limit the current (VCC / (R + 50 Ω)) to less than 15 mA. (The 50 Ω is the typical output impedance of the ISO784x.)

  • 0
    TI__Mastermind 18125 points

    Hi Zeev,

    As Clemens stated, the capacitor initially acts as a short between the output pin and the ground. Since the output current is more of a concern here, a proper resistor that limits the current must be chosen to limit the current to less than 15 mA. Keep in mind, that the absolute maximum rating for output current is -15mA to 15mA. exceeding these ratings can damage the device and we do not guarantee the performance of the device.

    Regards,
    Aaditya Vittal