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TIDA-01093: tida-01093- schematic connector-P2 & switch-S1

smash Micheal
Intellectual 1000 points
Part Number: TIDA-01093

Dear texas ,

What will be the situation when S1 switch is pressed & thermistor @ P2 is present ?

Please help to understand scenario, when both Thermistor @ P2 connector & Switch-S1 is pressed.

What am worried is following :-

  • Consider that, Thermistor @ P2 connector is left unused or absent or unmounted, and Switch S1 is pressed, than a momentary spike will be produced @ TS1 when ever Switch S1 is pressed due to D23 &C29 components.
  • Now consider @ P2 Thermistor is mounted, & some one presses switch S1, than due to presence of thermistor some voltage will always be available @ TS1 pin of AFE, due to which Switch press due to S1 wont be visible or if visible, than momentary Thermistor temp will be blanked, which is not undesirable.
  • Similarly the case is for connector P4 .

Please comment on above understanding.

Also what will be the scenario when charger not connected & Switch-S1 is pressed , will the MCU detect charger present, even when charger is not connected?

  • 0
    TI__Guru 54715 points

    Hi Rohit,

    D23 and D17 appear to be in parallell, both connect CHG_ACTIVATE to TS1_B.

    If the thermistor is not present TS1_B will charge to a voltage the diode drop below cell 1 (neglecting the voltage drop from the 3M resistors) with a time constant of about 16 us (R57, C27).  Current would begin to flow in C29 with about 2.4V on CHG_ACTIVATE slowing the rise of both the signal and the TS1_B voltage, but the part should already be booted.  Decay will be slower (C27 and R52, about 15 ms time constant).   

    With a thermistor present, the thermistor will divide the voltage with R57 to give a lower voltage at TS1, the lower resistance should have a shorter time constant.  If the switch is held the TS1 pin will see an incorrect voltage during the temperature sample. Having an additional source of current into the thermistor will raise its voltage which will make the temperature seem colder.  

    A similar effect will be observed at P4.

    Of course see the circuit description by the designer in the design guide at TIDA-01093 

    If a stuck switch is a concern in the system it would be best to design a pulse circuit to trigger boot of the devices and avoid continuous load on the cells.

    The MCU would likely know its environment, but it would not know at boot if boot had come from the button or the charger detect circuit.  Later in operation when the FETs were on the MCU would likely recognize an open thermistor condition and also that a CHG_DET signal would be from the button press.