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Several issues after loading supercap higher than 2.3V on i.MX7D board

Question asked by Dieter Möhrle on Mar 2, 2020
Latest reply on Mar 11, 2020 by Dieter Möhrle
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Several issues after loading supercap higher than 2.3V on i.MX7D board.

 

Brief description:

 

  • With the latest build 114 we enabled the charging of the supercap, i. e.:

    --> PF3000: in register 0xA1 (COINCTL) VCOIN was set to 111 (Voltage = 3,3V and COINCHEN = 1).
    --> Supercap is now charged correctly up to the selected load voltage 3,3V.

    Issue:

    As soon as the voltage of the supercap is higher than 2,3V and the power supply voltage is turned off the unit does not boot anymore. Also, we don't get any output on the serial debug interface anymore, the RESET-key has no function and further on flashing the firmware does not work, too.

    Actual results of our research:

    --> VIN_5V OK --> PMIC_PWR (3,7V) OK --> VLDO_3V3, MX7_RST_B and POR_B NOT OK approx. 1,58V (should be 3,3V)

    --> RESET input POR_B of the i.MX7D is on voltage level 1,58V --> Processor is in Reset?

    --> When the supercap will be discharged to less than 2,30V, the EWIO2 unit boots normally as known before and all voltages VLDO_3V3, MX7_RST_B and POR_B are set to 3,3V again. The RESET key, the serial debug interface and firmware flashing also works again.

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