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CSD83325L: Low current scenario and Rds (on)

Michael_SD
Prodigy 90 points
Part Number: CSD83325L
Other Parts Discussed in Thread: CSD85302L,

Hi,

We are evaluating using either CSD83325L or CSD85302L along with TI's BQ29700 for our single-cell lithium-polymer battery protection circuit.  Our use-case is for a very low power wearable device (30mAh cell and max operating current of < 100mA).  One of the important features of the battery protection circuit is over-current protection (both in the charge and discharge scenarios).  In order to predict the trip-point of the current protection, it is important to understand the Rds(on) behavior of the MOSFETs. 

Question:  is there a resource that you can share with me (datasheet, application note, or comment) that would help me better understand how Rds(on) for these MOSFETs varies at low currents (in the 20 - 300 mA range)?

Thanks in advance for your help,

Michael

  • 0
    TI__Mastermind 18200 points
    Michael,
    Assuming the MOSFET is fully enhanced (Vgs is at or greater than the minimum rated resistance spec, 2.5Vgs for each of these devices), the resistance really will not vary as a function of current (especially at these low currents well before the MOSFET is saturated) so much as it will as a function of temperature.

    This variation is provided in the datasheet in Figure 8. So whatever you believe the junction temperature of the device to be during this event, you can look up a temperature coefficient in Figure 8, and multiply all the resistance specs in the electrical characteristics table to get the new values at temperature.

    Obviously, we do still anticipate part to part variation for the typical resistance on a part at room temperature, so that's why we provide min and max resistances (at room temperature) in the datasheet that we recommend designing around.
  • 0 in reply to Brett Barr1
    Prodigy 90 points
    Thanks for the reply, Brett. Your response was very helpful!