MAX17843ACB datasheet(43/131 Pages) MAXIM

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The host should periodically update CBTIMER to ensure

that it does not count down to zero. If the countdown

timer is allowed to reach zero, the cell-balancing switches

are disabled until the timer is either disabled or refreshed

by writing a nonzero value.

To allow timed balancing with no host interaction, the

GPIO3 pin is configured to output a logic-high level while

the timer is counting using the GPIO3TMR configuration

bit of the GPIO register. An external diode is connected

from GPIO3 to SHDNL to prevent shutdown while the

timer is counting. Once the timer expires, the device shuts

down. The host may intervene prior to the timer expiring

to keep the device active and to reconfigure the device.

Emergency-Discharge Mode

The emergency-discharge mode performs cell-balancing

in a controlled manner so the cells can be discharged

to a safe level in the event of an emergency. The

BALSWDCHG and DEVCFG1 registers provide control

for this mode. A timeout value for the mode is configured

by DISCHGTIME[7:0], as shown in Table 15.

The emergency-discharge mode is activated by setting

the EMGCYDCHG bit with DCHGTIME[7:0] ≠ 00h. In

emergency-discharge mode, the following occurs:

1) The CBTIMER[3:0] is cleared to prevent the cell-

balancing watchdog from disabling the cell balancing.

2) Cell-balancing switches are controlled by

BALSWDCHG, not BALSWEN.

3) The discharge timer starts to count down.

4) Read-only counter DCHGCNTR[3:0] increments at

a 2Hz rate with periodic rollover at Fh. The host can

read this counter periodically to confirm the mode is

active.

5) The GPIO3 pin is driven high while the countdown is

active.

The emergency-discharge mode alternates between a

1-minute discharge cycle for odd cells and a 1-minute

discharge cycle for even cells. There is a 62.5ms minimum

off-time at the end of each discharge cycle to ensure no

overlap between even and odd discharge cycles. The

duty cycle of each discharge cycle can be configured by

DCHGWIN[2:0], as shown in Table 15.

By clearing EMGCYDCHG, the emergency-discharge

mode terminates and the following occurs:

1) The discharge timer is reset.

2) Control of the cell-balancing switches reverts to the

BALSWEN register.

3) Control of GPIO3 reverts to the GPIO register.

The emergency-discharge mode also terminates if

DCHGTIME[7:0] = 0h or the discharge time has reached

the configured timeout.

To prevent the emergency-discharge mode from terminat-

ing prematurely due to a device shutdown (which could

occur due to an extended lapse in host communications),

connect an external diode from GPIO3 to SHDNL to keep

SHDNL high while the timer is counting.

Table 15. Emergency Discharge Mode

FUNCTION

CONFIGURATION

BEHAVIOR

Duty cycle

DCHGWIN[2:0]

7.5s/bit

Switches on for 7.5s, off for 52.5s

Switches on for 15s, off for 45s

…

Switches on for 59.94s, off for 62.5ms

Timeout

DCHGTIME[7:0]

2 hours/bit

00h

Discharge mode disabled

01h

Discharge mode disabled after 4 hours

02h

Discharge mode disabled after 6 hours

…

FFh

Discharge mode disabled after 512 hours

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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