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using LTC3554 without bucks

I would like to know if we can use LTC3554 IC without using buck regulators (we want to use the IC only as battery charger with power path feature). I read in another post that if we want to use LTC3554 in this configuration it is suggest to connect FB1, FB2 pins to VOUT and leave unconnected SW1 and SW2. I have some doubts about button interface that can disable the power path control. We need to obtain a low quiescent current when VBUS=0 and VOUT will be connected to battery. If we put _ON=PWR_ON1=PWR_ON2=0 and successively we attach an external power (VBUS=5V) I understand, from a datasheet that in the button interface the machine goes in HR, PUP1 and PON states and from PON states will pass to PDN2 (because we have PWR_ON1=PWR_ON2=0) and POFF etc. and therefore it will never stay in PON state in stable manner. I think that this behaviour do not allow at power path control to attach battery at VOUT. I can put PWR_ON1=PWR_ON2=VOUT to stay in PON state. When the battery will be recharge and we will remove external power (VBUS=0) the PWR_ON1 and PWR_ON2 continue to stay at high level (vout passes fro VBUS to VBATT) and therefore tte button interface will remain in PON but the quiescent current will be 6.5uA and not 3uA, it is correct this assumption?

Many Thanks

Francesco

Parents
  • Hello,

    Just to clarify from the one sentence stating _ON=PWR_ON1=PWR_ON2=0. The /ON pin should not be help low permanently because it is an event triggered signal. It also has an internal pullup so it will take more current to hold it low. If PWR_ON1=PWR_ON2=0 and external power is applied then the PB state machine will operate as mentioned. To stay in POR at least one of the PWR_ONx pins needs to remain high. 

    The PB state machine does not affect the input or output ideal diode power paths. That is a function of VBUS, VBAT and VOUT voltage levels. The PB state machine does control the PBSTAT, and power up/down functions of the bucks. It is true that in the ON state with both bucks enable the Iq current will be higher than in the OFF or HRST states.

    The battery charger is also independent of the PB state machine.

Reply
  • Hello,

    Just to clarify from the one sentence stating _ON=PWR_ON1=PWR_ON2=0. The /ON pin should not be help low permanently because it is an event triggered signal. It also has an internal pullup so it will take more current to hold it low. If PWR_ON1=PWR_ON2=0 and external power is applied then the PB state machine will operate as mentioned. To stay in POR at least one of the PWR_ONx pins needs to remain high. 

    The PB state machine does not affect the input or output ideal diode power paths. That is a function of VBUS, VBAT and VOUT voltage levels. The PB state machine does control the PBSTAT, and power up/down functions of the bucks. It is true that in the ON state with both bucks enable the Iq current will be higher than in the OFF or HRST states.

    The battery charger is also independent of the PB state machine.

Children
  • Hello,

    thanks for your answer. Ok, in the meanwhile and from your answer I understand some things and I'm coming to this configuration in using LTC3554 without bucks:

    - SW1, SW2, _ON = unconnected

    - FB1, FB2 connected to Vout

    - PWR_ON1 and PWR_ON2 connected with pull-up to Vout

    With this configuration the PB state machine remains in PON state (after external power supplied) and the Power Path Circuitry and Battery Charger are not influenced by the behaviour of this machine but the IC draws the Iq current due to the two bucks enabled (probably we can connect one of PWR_ON pin to a port of microcontroller powered from Vout and after that microcontroller will be ready we can assert low this port to connect one of PWR_ON pin to ground to reduce Iq curret). Are you agree with this use of LTC3554 without using buck regulators?

    About BVIN pin, is it better to leave it unconnected or tied to Vout?

    Many Thanks and Best Regards

  • What was described sounds correct about how to connect the PWR_ONx pins. BVIN should be connected to VOUT to assure the internal regulator circuitry is in the correct state. It should not float.