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TPS548A28: MODE selection register

Toshiro Imi
Expert 6580 points
Part Number: TPS548A28

Hello,

Our customer plans to use 33k-ohm+/-5% (31.35k to 34.65k-ohm) to GND on MODE pin in order to FCCM/800kHz operation. Then, he is afraid that the device does not function if the register raises higher than 30.1k+10% (33.11k-ohm) specified in the datasheet Table.-7.1.

Could you please help him out  following points

-  What is happened in above case.

-  Does TPS548A28 works normally (FCCM/800kHz) as long as the register is set in 30.1k-ohm +/-10% range, even if +/-5% accuracy register to use.

- If possible, could you please share the MODE Selection functional block diagram with him.

Best regards,

  • +1
    TI__Mastermind 20125 points

    In the above described case, the MODE will decode to 800kHz/FCCM or 1000kHz/FCCM . 

    We test and guarantee the device with the 30.1kohm +/-10% range.     

    If a customer uses a resistance outside the range,  it will decode either upper or lower setting. 

    Most, likely the device will decode to the setting it is closest.   

    The block diagram is simple. 

    A current source to the MODE pin, a comparator and voltage sources representing the mode selections. 

    The current source and external mode resistor create a voltage that is compared to the different voltages levels that represent the mode selections. 

    The pin voltage decodes to the mode setting. 

    The customer can place a resistor that is closest  to 33k-ohm +5% and see how it decodes.   Keep it mind if there are test or design changes in the future that a solution that was designed outside the margins will be at risk.