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TPS53355: Using PGOOD signal for sequencing and resetting a CPU

ALEXANDROS APOSTOLIDIS
Prodigy 120 points
Part Number: TPS53355
Other Parts Discussed in Thread: AM6412,

Hello,

I will be using an ARM CPU (AM6412) and for its POR and Power up sequencing I am thinking of using the PGOOD signal.

Using the PGOOD signal of the 1st PS , to enable the 2nd etc...I will achieve the power up sequence target.

Using all the relevant (to CPU) PGOOD signals , and OR-ing them , I can feed the output to the main POR reset in CPU signal...eliminating the use of a Supervisory circuit.

Is this solution smt TI suggest ?

Thanks

Alex

  • 0
    TI__Mastermind 32400 points

    Hello, 

    From what you described it sounded like a good use of PG. 

    Can you draw a high level diagram and power sequencing timing of what you are trying to achieve. the PG has delays (1ms delay) just making sure that is taken in consideration. also, PG will be triggered with Overshoot on VOUT of 110%. that may cause a POR in you sequence. see below  

    thanks 

    Tahar

  • 0
    TI__Guru 56985 points

     

    Yes, this is the most common usage of PGOOD.

    In most applications, the last converter in the sequencing will send it's PGOOD to the CPU, rather than a massive AND of all of the PGOOD signals, since the sequencing will force the last converter to remain off until all the other converters are "Power Good" and will shut down the last converter if any prior converter becomes "power bad"  However, the ANDing logic can still work.

    One caution, some devices have limitations, or voltage requirements on their Enable inputs that might not make them compatible with the AND logic, or the CPU input.  For example, some devices share their DISABLE function with their Soft-start, others might clamp their EN pin at a lower voltage, still others might need 1.5 or even 2V to enable.  This is generally not an issue with Open Drain PGOOD pins, since they can be pulled up to a voltage that is compatible with the next stage, but the voltage levels at the EN pins may not be compatible with the AND logic, which might need level shifters.

    Also, the PGOOD pin is sometimes used for controlling the MODE pin on the TPS53355, so that the MODE pin can be pulled to GND during power-up, than pulled up later to switch from Autoskip to Forced Continuous Conduction.  IF PGOOD is used in this way, it needs to be pulled up above 2V to ensure the MODE selection changes to FCCM.  Depending on the needs and voltage limitations on the next-stage EN, additional circuitry may be required.