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ISO7740: ISO7740

Part Number: ISO7740


In design, ISO7740 output channels (each channel) are connected to LED for indication. The LED sink current is around 3mA.

Whether output channels (each channel) are able to handle the 3mA current (sink) ?

Please clarify. Below attached the circuit diagram for your reference.

Thanks & Regards,

Venkata Seshathri.S

  • Hi Venkata,

    Welcome to TI E2E Forum and thank you for your interest in ISO7740.

    Device ISO7740 only supports a maximum of ±2mA of source / sink current with 3.3V VCC while it can support ±4mA for 5V VCC, this is also stated in ISO7740 datasheet as shown below. Please note that the device doesn't have any internal current limit or clamp and hence, it is the responsibility of the circuit designer to make sure the output source / sink current is not violated. When ISO7740 is interfaced to other digital devices (like MCU) then the currents are going to be well within the limits. But when it is connected to sourcing or sinking load (like in this case), sufficient current limiting resistance needs to be used to not exceed the recommended values.

    Assuming a forward voltage (VF) of 1.7V and typical value of VOH as 0.1V, the sinking current into device in this case can be calculated as IL = (3.3V - 1.7V - 0.1V) / 200Ω = 7.5mA. This current is exceeding the max current supported by ISO7740 but maybe the LED in your application has higher forward voltage than 1.7V. Please do make sure the resistor values are chosen accordingly, thanks.

    Koteshwar Rao

  • Hi Venkata,

    I had earlier responded assuming a VCC of 5V, later I noticed that you are using 3.3V for VCC. I have updated the above post accordingly.

    Please note that the device doesn't support 3mA of load for 3.3V VCC2 but if you can increase VCC2 voltage to 5V then you will be able to use it upto 4mA of load current. Thanks.

    Koteshwar Rao