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ISOW7842: ISOW7842 output power limit.

Racheal Shen
Prodigy 121 points
Part Number: ISOW7842
Other Parts Discussed in Thread: ISO1050, SN6501

Tool/software:

Hello Here,

This is Racheal from Shenzhen site AA3 team. My customer InfyPower wants to use ISOW7842 in their products. Here is the application info:

ISOW7842 selection reason: update from ISO1050, with DCDC integrated inside ISOW7842, aux-power simplified.

Input VDD: 3.3V

signal chain: DSP – Isolation – CAN transceiver(NON-ISO)

Output current: 100mA.

Output VDD: 5V

The datasheet indicates the device capable of outputting over 40mA. But this still cannot meet the customer’s need. So we’d like to know what’s the exact limit?

Because the customer believes that this device cannot output 100mA, he selects NSIP8842 as isolation device, which applies 3.3V_VIO and 5V_VDD in the primary side separately. If ISOW7842 is not suitable to the application scenario, could you recommend other solutions?

 

 

Thanks,

Racheal Shen

  • 0
    TI__Mastermind 29305 points

    Hello Racheal, 

    Thank you for reaching out. ISOW7842 actually outputs more power than the NSIP8842. The ISOW datasheet states that the isolated supply outputs up to 0.65W if isolated power while the NSIP datasheet states "the isolated DC-DC converter provides up to 500mW output power...". However, some current is needed to supply the secondary side of the isolator. The ISOW7842 has at least 100mA available to the solution according to the datasheet (please note that this is the 5-V Input, 3.3-V Output use case). 

    From my understanding, the NSIP device has a similar output supply current of 100mA 

    The 40mA is the current from the local supply. The specs shown are both the current available at the output supply. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Prodigy 121 points

    Thanks for your reply.

    I think we have to make clear the details. The customer referred to the application of 3.3Vin and 5Vout, and 3.3V supply for the DSP. He wants to use the secondary 5V to supply other aux circuit. In this way, the aux power can be simplified. While the Iiso(out) is indicated as about 40mA in this case. If the supply current for a DSP device is around 80mA, it's not possible to reverse ISOW7842 direction to 5Vin 3.3Vout. 

    The NSIP8842 meets his need for it can output current 100mA, by setting the logic threshold by 0.7xVDDL (7x3.3V, VDDL is NSIP8842 pin7), implementing DCDC using primary power VDD of 5V.

  • +1 in reply to Racheal Shen
    TI__Mastermind 29305 points

    Hello Racheal,

    Thank you for the clarification, I understand now that you need 80mA to supply power to a DSP. ISOW7842 only supports a boost mode configuration (3.3V --> 5V conversion) up to 40mA. Below are some previous E2E posts for some extra details. 

    Based on the NSIP8842 datasheet, the part doesn't support 3.3V to 5V conversion (below snippets). 

     

    It would be better for the customer to use SN6501 and a transformer or an isolated DC to DC converter to provide power to the isolated side. 

    Best,
    Andrew