should generally be floating before they are connected to the appropriate cell. It is expected that transient
current will flow briefly when each cell is attached, but the cell voltages will quickly stabilize to a state without
DC current flowing through the diodes. However, if a large capacitance is included between a cell input pin
and another terminal (such as VSS or another cell input pin), the transient current may become excessive
and lead to device heating. Therefore, it is recommended to limit capacitances applied at each cell input pin
to the values recommended in the specifications.
16.4 Startup Timing
At initial power up of the BQ769142 device from a SHUTDOWN state, the device progresses through a
sequence of events before entering NORMAL mode operation. These are described below for an example
configuration, with approximate timing shown for the cases when
[FASTADC]
= 0 and
[FASTADC]
= 1.
Note
When the device is configured for autonomous FET control (that is,
[FET_EN]
= 1), the decision to
enable FETs is only evaluated every 250 ms while in NORMAL mode, which is why the FETs are not
enabled until approximately 280 ms after the wakeup event, even though the data was available
earlier.
Table 16-2. Startup Sequence and Timing
Step
Comment
FASTADC Setting
Time (relative to wakeup event)
Wakeup event
Either the TS2 pin is pulled low,
or the LD pin is pulled up,
triggering the device to exit
SHUTDOWN mode.
0, 1
0
REG1 powered
This was measured with the OTP
programmed to autonomously
power the REG1 LDO.
0, 1
20 ms
INITSTART asserted
This was measured with the OTP
programmed to provide the
INITSTART bit in the Alarm signal
on the ALERT pin.
0, 1
23 ms
INITCOMP and ADSCAN
asserted
This was measured with the OTP
programmed to provide the
INITCOMP and ADSCAN bits in
the Alarm signal on the ALERT
pin.
0
88 ms
1
58 ms
FULLSCAN asserted
This was measured with the OTP
programmed to provide the
FULLSCAN bit in the Alarm
signal on the ALERT pin.
0
221 ms
1
129 ms
FETs enabled
This was measured with the OTP
programmed to autonomously
enable FETs.
0
282 ms
1
284 ms
shows an example of an oscilloscope plot of a startup sequence with the device configured in OTP
with
[FASTADC]
= 1,
[FET_EN]
= 1 for autonomous FET control, setup to use three thermistors, and providing
the
[INITCOMP]
flag on the ALERT pin. The TS2 pin is pulled low to initiate device wakeup from SHUTDOWN.
SLUSE91A – SEPTEMBER 2020 – REVISED FEBRUARY 2021
68
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