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SN65HVD3082E: Can "R" output terminal drive LED side of opt coupler with 15mA as maximum?

Kazuya Nakai59
Guru 20130 points
Part Number: SN65HVD3082E
Other Parts Discussed in Thread: ISO1500, ISO1410

Hello guys,

One of my customers is considering using SN65HVD3082E for their new products.

They have the following question about SN65HVD3082E. Could you please give me your reply for them?

Q1. I want to driver LED of a opt coupler with about 15mA as maximum by "R" output terminal of the device.

     This 15mA is a pulse current not constant current. And the average current of LED driving will be less than 8mA of the recommended value.

     Can "R" output terminal drive LED side of opt coupler with 15mA as maximum? 

Q2. I think the average current of "R" output current must be less than +\-8mA.

      Also I think the peak current (very small on duty) of "R" output current must be less than +\-24mA.

     Is my understanding correct?

Your reply would be much appreciated.

Best regards,

Kazuya.  

       

  • 0
    Guru 244110 points

    It is possible to try to sink 15 mA into the output. However, the maximum current for which VOL is guaranteed is 8 mA, so the VOL at 15 mA could be much higher.

    You are correct that 24 mA must never be exceeded.

    Is 15 mA really necessary? It might be possible to use a higher load resistance for the optocoupler. (And a digital optocoupler like the H11L1 needs only 1.6 mA, and there are isolated RS-485 transceivers like the ISO1500 or ISO1410.)

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 48215 points

    Thank for the help Clemens!

    Hi Kazuya,

    Let us know if we can help with any of Clemens' recommendations. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Guru 20130 points

    Hello Eric and Clemens,

    Thank you very much for your reply.

    I told them that TI didn't recommend to driver over 8mA by "R" output terminal.

    They gave me the following questions after that.

    Q1, Why is there 3 times current difference between the recommended condition (8mA)

          and the absolute maximum condition (24mA)?

    Q2. We will use SN65HVD3082E under VCC=4.6V~5.4V and  -20~+85 degree C conditions. 

          In these conditions, can the recommended "R" output drive current be increased from 8mA?

    Q3. In any condition, is the "R" output drive current which can be guaranteed by TI 8mA ?

     Could you give me your reply for them? 

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 48215 points

    Hi Kazuya,

    (Q1) The recommended specification describes the output current the device can maintain while still meeting all other specifications such as output voltage. This applies across all operating conditions including temperature and supply voltage range (Q3). The absolute maximum condition describes the limit of the device before damage may occur. Once the recommended max is exceeded, the device behavior is no longer guaranteed. However, the device will not experience damage until the absolute maximum specification is exceeded. 

    (Q2) These conditions are very close to the operating range for the device, so an extension of this recommended current is not advisable. It is likely that the result of drawing more than 8mA will be that the specified output voltage will not be reached. This may be something you experiment with under your requirements to see what behavior changes. As long as the current remains under the absolute max, no damage should occur from the extra draw. 

    Have you been able to review Clemens recommendation of ISO1500 or ISO1410 to see if an integrated isolator/transceiver solution may be viable here?

    Regards,
    Eric Schott