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Original question:

BQ21062: without Vin

BQ21062: Device not entering ship mode if VBAT goes below VBATUVLO (VIN not present)

user5932623
Prodigy 80 points
Part Number: BQ21062

Hi,

we measured quiescent currents on our hardware and found that the BQ21062 doesn't enter ship mode if the battery voltage drops below UVLO. The intended behavior would be entering ship mode and draw the lowest possible current to protect the battery from deep discharge.

What we did (scenario 1):

  1. First time supply VBAT = 3.3V and VIN = 5.0V, then VIN disconnected
  2. BQ21062 enters ship mode and draws lowest possible current --> OK
  3. VBAT is slowly reduced to 2.8V (default UVLO) --> Quiescent current increases to 2.67µA
  4. VBAT is slowly further reduced to 2.5V --> Quiescent current stays constant at 2.67µA
  5. VBAT is slowly increased to 3.2V --> BQ21062 enters ship mode and draws lowest possible current.
  6. VBAT is slowly reduced to 2.8V --> BQ21062 stays in ship mode

Same behavior with activated internal LDO (scenario 2):

  1. First time supply VBAT = 3.3V and VIN = 5.0V
  2. I2C Communication to activate internal LDO with 2.8V output voltage: 0xD6 0x1D 0xD8
  3. VIN disconnected 
  4. BQ21062 supplies system with 2.8V. With µc in sleep mode we measure 3.5µA --> OK
  5. VBAT is slowly reduced to 2.8V (default UVLO) --> internal LDO is disabled --> Quiescent current decreases to 2.67µA
  6. VBAT is slowly further reduced to 2.5V --> Quiescent current stays constant at 2.67µA
  7. VBAT is slowly increased to 3.2V --> BQ21062 enters ship mode and draws lowest possible current.
  8. VBAT is slowly reduced to 2.8V --> BQ21062 stays in ship mode

If VIN was present, then the device will not enter ship mode (scenario 2) or stay in ship mode (scenario 1)  as soon as UVLO is reached. Instead the quiescence current is at approx. 2.67µA. We observe the same behavior on two different PCBs and can shift the voltage level for the 2.67µA quiescent current with configuration of UVLO (tested 2.6V and 3.0V).

Could you please confirm or verify this behavior and suggest a workaround? The problem we see is the deactivated LDO (which supplies our system) as soon as UVLO is reached. We would not even have a chance to enable ship mode via I2C.

Thanks in advance and best regards,

Marc

  • 0
    TI__Genius 14045 points

    Hi Marc,

    I will confirm this behavior in lab and follow up.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Genius 14045 points

    Hi Marc,

    If I understand correctly the issue is that you are seeing 2.67uA current draw while the device is meant to be in shipmode?

    user5932623 said:
    If VIN was present, then the device will not enter ship mode (scenario 2) or stay in ship mode (scenario 1)  as soon as UVLO is reached.

    To clarify, in order to enter shipmode VIN must be less than Vuvlo.

    user5932623 said:
    The problem we see is the deactivated LDO (which supplies our system) as soon as UVLO is reached. We would not even have a chance to enable ship mode via I2C

    When VBAT crosses the UVLO threshold the device is shutoff and the regulators are deactivated. VBAT must be above Vbuvlo to power regulators otherwise the battery may become critically discharged. Typically, the device is entered into shipmode when powered by a charged battery before being shipped in a factory/production setting. Are you hoping to use the shipmode as a sleep state?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 80 points

    Hi Juan,

    the BQ21062 draws 2.67uA current, as soon as VBAT crosses UVLO threshold (VBAT <= UVLO). As long as VBAT > UVLO, the current is far below. As mentioned above, the pre-condition is, that VIN was present and has been disconnected, which presumably puts the BQ21062 in Ship Mode (Datasheet 9.4.1: "The device will also enter Ship Mode upon battery insertion when no valid VIN is present."). Unfortunately when VBAT crosses UVLO (VBAT <= UVLO), the BQ21062 seems to leave ship mode and deep-discharges the battery with 2.67uA current.

    In case we have enabled the LDO output on the BQ21062 via I2C while was VIN was present, we see that it shuts off PMID and LS/LDO as soon as VBAT crosses UVLO (VBAT <= UVLO). But instead of automatically entering Ship Mode to avoid deep-discharging the cell, it also draws 2.67 uA from the battery.

    The expected behavior is what you wrote two moths ago here: BQ21062: without Vin

    "If VIN is not present and VBAT < VBATUVLO then the device will enter ship mode."

    Thanks and best regards,

    Marc

  • +1 in reply to user5932623
    TI__Genius 14045 points

    Hi Marc,

    Apologies for the oversimplification. Although functionally, the device is similar to ship mode without /MR functionality the state is not truly in shipmode and will not provide the same quiescent current as a ship mode device. Typically, Vbuvlo is provided more as a protection threshold to shutdown certain functionality of the IC that may not be properly biased with a low battery voltage and is not really intended as a functionality to enter a sleep mode.

    Typically, for an application it is best to enter Shipmode before Battery voltage approaches BUVLO as a means to conserve battery rather than relying on the BUVLO threshold to disable regulators.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 80 points

    Hi Juan,

    thanks for the clarification. Would be nice to see such a deep-discharge protection feature in a successor device.

    Best regards,

    Marc