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TPS653853-Q1: About Keep Alive Circuit

Yuya Shoji
Expert 3480 points
Part Number: TPS653853-Q1
Other Parts Discussed in Thread: TPS653853A-Q1, TPS653854A-Q1

Hi team,

I'm BCCing this to the customer because following question is based on the customer inquiry.

I heard that Keep alive circuit is mandatory to feed the power to its internal digital core. In my understanding, only big capacitance can work for it if this line contains R internally. Could you tell me the reason why the circuit needs for R? (I'm assuming this is to gain big τ.)

Along above question, I'd like to know what internal circuit block mainly consume the capacitance of C_VDD6 and C_VDD6_KEEP_ALIVE in COLD CRANK.

Best regards,

Shoji 

  • +1
    TI__Intellectual 1215 points

    Hello Shoji-san,

    the R in series is only needed to make the big C "invisible" for the BUCK-BOOST regulator during normal operation. For normal operation, the VDD6 BUCK-BOOST has a max. allowed CVDD6 of 47uF. So with this R=10Ohms, the big C for keep-alive does not affect the normal voltage regulation of the VDD6 BUCK-BOOST.

    The current consumption from C_VDD6 and C_VDD6_KEEP_ALIVE comes from the Low-Power SAM Mode of the Steering Angle Monitor. Please refer to datasheet "TPS653853A-Q1_TPS653854A-Q1_SLVSF95_Confidential-NDA_Restrictions.pdf", Figure 5.26 Low-Power SAM Mode Phases. Calculation examples to determine the needed C_VDD6_KEEPALIVE are given in section 6.2.2.1.1 VDD6 Impact When Low-Power SAM Mode is Used

  • 0 in reply to Jacobus Adrianus van Oevelen
    TI__Expert 3480 points

    Hi Jacobus,

    Understood.

    What will happen if the C_VDD6_KEEP_ALIVE is much bigger than the calculated value? Will it have bad influence on the system?

    Best regards,

    Shoji