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BQ25570 reverse voltage protection using TLV3691 comparator

Other Parts Discussed in Thread: TLV3691, TIDA-00246


i am trying to understand how the reverse voltage protection implemented in the TIDU808 document, section 3.5

works on startup if the battery serving VBAT/AFE 3.6 V is depleted and the comparator has no supply voltage. will the circuit ever start up from a TEG power source?



  • When VSTOR voltage is less than 1.8V, the IC requires at lest 15uW input power to start up in cold start. Typically, with Li-ion batteries, the voltage of the battery does not drop below 1.8V. In main boost mode, the minimum input power for normal charging is 5uW.

  • yes, that is clear. that's the spec of the MPPT harvesting frontend on the BQ255*

    but in this specific design VIN_DC is switched using a a CSD13202 FET which is driven from a TLV3691 comparator. and this comparator does not have any power when V_BAT is down. so there will be no input power to harvest from.

    maybe it helps if you know the actual issue i am trying to solve: i need to be able to harvest from a bipolar power source (TEG in environmental monitoring. not from process heat. it's a very long lived application and it can be that the TEG will be covered with snow for half a year or so. if the battery is not enough to sustain during that time, the circuit should be able to start up automatically when harvesting is again possible...
  • hello,

    i have another issue regarding the TIDU808 app note and the design TIDA-00246:

    i implemented the front end protection from figure 13 using the TLV3691 and CSD13202. however i cannot get the FET to switch although the comparator is working correctly when i create a spice model using the TI supplied TINA spice components. when i change the compator polarity i get the FET to switch, but it rectifies into the negative, not the positive voltage. when i replace the FET for a p-channel type, eg. CSD25310, it works. but not using the n-channel fet as suggested in TIDU808. so i would like to know is the design correct? has anyone ever measured this design to protect successfully against negative input voltages or is this a clear error in the design?

  • I have also doubt in this part. N mosfet cannot pass positive voltage from drain to source completely (not strong one). N -Mos will drop Vgsth across source and drain.  But if we use a P mos instead of N mos it can pass positive voltage completely from teg (drain ) to IC( source) without any drop.