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TMS320F28335: Abnormal power supply startup

Rain Wang
Expert 1400 points
Part Number: TMS320F28335
Other Parts Discussed in Thread: LP2992

Hi TI

1. The customer's TMS320F28335 occasionally has a startup exception: from the phenomenon, it seems that the kernel is not up;

2. In case of abnormality, press the reset key to operate normally;

3. The 1.8V and 3.3V of the measured power supply are normal in case of problems;

4. For 600pcs of boards running on site, 5~10 boards will have this abnormality each time they are powered on, and the boards with problems are not fixed;

The customer did not consider the 1.8V and 3.3V power on sequence when designing the PCB. Because the customer uses LP2992 to convert 3.3V to 1.8V, 1.8V will lag behind the 3.3V power supply. Does TMS320F28335 have any restrictions on the order of 1.8V and 3.3V power supply? Please see the figure below for the customer's power supply design. Thank you.

      

  • 0
    TI__Guru* 95315 points

    Rain,

         There some requirements not only for power-up, but also for power-down. From the datasheet:

    "power the VDD (core voltage) pins prior to or simultaneously with the VDDIO (input/output voltage) pins, ensuring that the VDD pins have reached 0.7 V before or at the same time as the VDDIO pins reach 0.7 V."

    "There are some requirements on the XRS pin:
    1. During power up, the XRS pin must be held low for tw(RSL1) after the input clock is stable (see Section 7.9.2.2). This is to enable the entire device to start from a known condition.
    2. During power down, the XRS pin must be pulled low at least 8 μs prior to VDD reaching 1.5 V. Meeting this requirement is important to help prevent unintended flash program or erase."

    I also noticed two issues with LP2992:

    1. To operate 28335 at 150 MHz, you need 1.9v, not 1.8v.
    2. LP2992's maximum output current is only 250 mA, whereas the max current consumption of 28335 is 315 mA. as a good design practice, you should have adequate margin to account for in-rush current, so the LDO used should have a rated current of at least 400 mA.

    As you can see, there are multiple issues with customer's design.

  • 0 in reply to Hareesh Janakiraman
    Expert 1400 points

    Dear Hareesh

             OK, thanks for your support.