ADBMS1818CSWAZ-R7 datasheet(39/92 Pages) AD

39 / 92 page

Data Sheet

ADBMS1818

THEORY OF OPERATION

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Rev. B | 39 of 92

Thermal Shutdown

To protect the ADBMS1818 from overheating, there is a thermal

shutdown circuit included inside the IC. If the temperature detected

on the die rises above approximately 150°C, the thermal shutdown

circuit trips and resets the configuration register groups and S

Control Register Group (including S control bits in PWM/S Control

switches. When a thermal shutdown event has occurred, the THSD

bit in Status Register Group B goes high. The CLRSTAT command

can also set the THSD bit high for diagnostic purposes. This bit

is cleared when a read operation is performed on Status Register

Group B (RDSTATB command). The CLRSTAT command sets the

THSD bit high for diagnostic purposes but does not reset the

configuration register groups.

Revision Code

The Status Register Group B contains a 4-bit revision code (REV).

If software detection of the device revision is necessary, contact

the factory for details. Otherwise, ignore the code. In all cases,

however, the values of all bits must be used when calculating the

packet error code (PEC) on data reads.

WATCHDOG AND DISCHARGE TIMER

When there is no valid command for more than 2 seconds, the

watchdog timer expires, which resets the configuration register

bytes CFGAR0-3 and the GPIO bits in Configuration Register

Group B in all cases. CFGAR4, CFGAR5, the S Control Register

Group (including S control bits in PWM/S Control Register Group

B) and the remainder of Configuration Register Group B are reset

by the watchdog timer when the discharge timer is disabled. The

WDT pin is pulled high by the external pull-up when the watchdog

time elapses. The watchdog timer is always enabled, and the timer

resets after every valid command with matching command PEC.

The discharge timer is used to keep the discharge switches turned

on for programmable time duration. If the discharge timer is being

used, the discharge switches are not turned off when the watchdog

timer is activated.

To enable the discharge timer, connect the DTEN pin to VREG (see

Figure 63). In this configuration, the discharge switches remain on

for the programmed time duration that is determined by the DCTO

value written in Configuration Register Group A. Table 33 shows the

various time settings and the corresponding DCTO value.

Figure 63. Watchdog and Discharge Timer

Table 32. DCTO Settings

DCTO

Time

(Minutes)

Disabled 0.5

120

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