MAX17823H datasheet(40/129 Pages) MAXIM

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Emergency-Discharge Mode

The emergency-discharge mode performs cell balanc-

ing in a controlled manner so that the cells can be dis-

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

BALSWDCHG and DEVCFG2 registers provide control for

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

DISCHGTIME[7:0] as shown in Table 13.

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 BALSWD-

CHG, not BALSWEN.

3) The discharge timer starts to countdown.

4) The read-only counter DCHGCNTR[3:0] increments

at a 2Hz rate with periodic roll-over at Fh. The host

can read this counter periodically to confirm that 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 13.

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 13. 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

MAX17823H

12-Channel, High-Voltage

Data-Acquisition Systems

www.maximintegrated.com

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