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ADS7040: The sink and source current of ADS7040

Skylar Li
Intellectual 1030 points
Part Number: ADS7040

Tool/software:

Hi Experts,

This is Skylar responsible for GREE.

1. Could you pls tell me the sink and source current of SDO of ADS7040? 

2.  Here is the sch as below. The sink and source current of CLK and CS of M0G1506 is 6mA.

a. Could you pls help check what the exact value of R1 that ADS7040 could support (the range of R1 is welcome)

b. Could you pls help check what value of R2 and R3 could work? The ds of opto-coupler is attached.

  Toshiba-TLP785.pdf

BR,

Skylar

  • 0
    TI__Intellectual 2910 points

    Hi Skylar,

    1. The digital I/O of the ADS7040 can sink and source a maximum of 2mA

    2a. The value of R1 won't impact the operation of the ADS7040 since it is on the other side of the opto-isolator

    2b. R2 will be dependent on the current the transistor needs at its base to conduct. For R3, 1k ohm seems to be within the correct range, but this might have to be adjusted depending on the properties of the transistor and how fast the transitions occur.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    TI__Intellectual 1030 points

    Hi Joel,

    Thanks for your answer.

    Joel Meraz said:

    1. The digital I/O of the ADS7040 can sink and source a maximum of 2mA

    Do you mean that the transient current of digital I/O of the ADS7040 should not over 2mA or the transient current could be 4mA, but we could only satisfy the RMS current would not be over 2mA?

    Is it acceptable for us about the over 4mA transient current and less than 2 mA RMS value?

    Meanwhile, may I ask your recommendations about the R1, R2 and R3? Thanks.

    BR,

    Skylar

  • 0 in reply to Skylar Li
    TI__Intellectual 2910 points

    Hi Skylar,

    While transient currents over 2mA might be possible, it is not recommended to exceed this threshold at all. This could lead to damaging the digital communications circuit internal to the device, or contribute to artificial aging of the device. Since this device is intended to consume ultra-low power, it is never really expected to source as much current as might be required for the opto-isolator LED, especially over an extended period of time.

    As for the value of R1, R2, and R3, these values will be completely independent of the ADS7040, so I'm unable to make a recommendation. These values will be dependent only on the opto-isolator's characteristics, so I would consult that particular datasheet. 

    Regards,
    Joel