• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 34 subscribers
  • Views 302 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.

SN75C1167: About output current

Ryu Yamashita
Genius 3705 points
Part Number: SN75C1167

Hi team,

I think the drive current will flow 50mA when the power supply is 5V and the termination resistor is 100Ω connected.
But is it limited to 20mA by the clamp current (Iok)?
If the instantaneous drive current exceeds 150mA, is it impossible to clamp and will it be destroyed?

Sincerely.
Ryu

  • +1
    Guru 317210 points

    Output current and clamp current are different. The clamp current specifies the maximum current that is allowed to flow through the clamping diodes when you apply a voltage below GND or above VCC (see the input/output schematics). If there are such voltages, your circuit must limit the current to below 20 mA to prevent the device from being damaged.

    When you connect a 100 Ω load to the outputs, the differential output voltage is at least 2 V, and typically 3.1 V. This implies that the output current is at least 20 mA, and typically 31 mA.

    When you connect another load, your circuit must limit the current to below 150 mA to prevent the device from being damaged. (When you short the two outputs to each other or to some other voltage in the ±7 V range, the current might be larger than 150 mA.)

  • 0 in reply to Clemens Ladisch
    Genius 3705 points

    Hi Clemens

    Thanks for reply.
    You say 31mA typically, but the recommended value on the datasheet is MAX 20mA, does that mean it is OK?

    Sincerely.
    Ryu

  • 0 in reply to Ryu Yamashita
    Guru 317210 points

    Yes, these two specifications are somewhat contradictory.

    Anyway, this device is designed to work with a 100 Ω load. Just use that.

  • +1 in reply to Ryu Yamashita
    TI__Guru 52332 points

    Hi Ryu,

    Clemens is correct - the output driver current max is different than the clamp current - using a 100 Ohm load is ok as that is a normal RS-485 termination. The clamp current is only when the clamp diodes are forward biased which is when the input voltage w.r.t. ground is <GND or >Vcc.

    If you have any other questions please let me know!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Genius 3705 points

    Hi Paker,

    Thanks for reply.
    I understand.

    Sincerely.
    Ryu