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Original question:

BQ28Z610-R1: High side N MOSFET state in under voltage

BQ28Z610-R1: ZVCHG Exit Threshold Behaviour

18311
Prodigy 10 points
Part Number: BQ28Z610-R1
Other Parts Discussed in Thread: BQ24022

Hi,

We have altered the ZVCHG Exit Threshold value from it's default value (2200mV) to 0mv (Zero).

This appears to effectively stop charging from a cell voltage of 970mV all the way down to 0V.

The setup is as follows:

The Cell voltage is simulated by a NGL201 Sink-Source Power Supply

PACK terminals are connected to a BQ24022 which means that 4.2V is applied to the PACK terninals

Cell voltage is then increased in 10mV steps from 0V Up to 970mV and no charging current can be measured

If Cell voltage is instead reduced from 1.10V and down, the charging is still inhibited at 970mV - so it works in both directions

At a cell voltage of 980mV low charge current can be measured - about 10mA

The charge current increase with cell voltage until the cell voltage reaches 1.05V at which the current starts pulsating wih 20ms interval

Another observation:

If the ZVCHG Exit Threshold is set to ex. 500mV then charging is allowed from 0V up to 500mV where it then stops until the cell voltage reach 970mV

There seem to be some crossover zone between 970 - 980mV, any ideas on what happens around 970 - 980mV cell voltage?

Any suggestions on how to prevent charging below 1.30V?

Best regards,

Klaus

  • 0
    TI__Guru** 102935 points

    Hello Klaus,

    Can you share the waveforms you are seeing (the pulsing and the current @ different voltages)

    We can take a closer look at this.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 10 points

    Hi Wyatt,

    Attached scope plots show pulsating at different cell voltages.

    It looks like the CHG and DSG FET's open and cause the voltage to drop down to the cell voltage level, and the shut's off again.

    Yellow: PACK voltage

    Blue:    Cell Current

    Green: Charge IC Supply (5V), Charger is in USB / 500mA mode

    Vcell-970mV - No current flow and PACK stable at 4.2V (Charger Float voltage)

    Vcell-1025mV - Average current draw of 75mA, PACK stable at 4.2V

    Vcell-1025mV-Zoom - Current is pulsating and peaks are 130us apart

    Vcell-1050mV - PACK drops periodically down to cell voltage, but for a short time. Average current draw is 30mA

    Vcell-1100mV - PACK has sharp drops down to cell voltage and stays down for a few ms and repeats every 22ms. Average current is 30mA and peaks about 300mA

    Vcell-1200mV - Same behaviour as with 1100mV but peaks are more than 400mA

    Vcell-1200mV-Zoom

    Vcell-2400mV - At this cell voltage the peak current is almost 2A and a steady 450mA for about 5ms

    The pulsating stops at a cell voltage just above 2500mV and the charger is now able to supply a steady precharge current of 67mA

    Anything else, let me know.

    Best regards,

    Klaus

  • 0 in reply to 18311
    TI__Mastermind 19195 points

    Hi Klaus,

    Its not possible to disable the ZVCHG feature.

    Sorry about that.