ADBMS1818ASWZ-R7 datasheet(25/92 Pages) AD

25 / 92 page

Data Sheet

ADBMS1818

THEORY OF OPERATION

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Rev. B | 25 of 92

STATE DIAGRAM

The operation of the ADBMS1818 is divided into two separate

sections: the core circuit and the isoSPI circuit. Both sections have

an independent set of operating states, as well as a shutdown

timeout.

ADBMS1818 CORE STATE DESCRIPTIONS

Sleep State

The reference and ADCs are powered down. The watchdog timer

(see the Watchdog and Discharge Timer section) has timed out.

The discharge timer is either disabled or timed out. The supply

currents are reduced to minimum levels. The isoSPI ports are in the

idle state. The DRIVE pin is 0 V.

If a wake-up signal is received (see the Waking Up the Serial

Interface section), the ADBMS1818 enters the standby state.

Standby State

The reference and the ADCs are off. The watchdog timer and/or

the discharge timer is running. The DRIVE pin powers the VREG

pin to 5 V through an external transistor. Alternatively, VREG can be

When a valid ADC command is received or the REFON bit is set

to 1 in Configuration Register Group A, the IC pauses for tREFUP to

allow the reference to power up and then enters either the REFUP

or measure state. Otherwise, if no valid commands are received for

tSLEEP (when both the watchdog and discharge timer expire), the

ADBMS1818 returns to the sleep state. If the discharge timer is

disabled, only the watchdog timer is relevant.

REFUP State

To reach this state, the REFON bit in Configuration Register Group

A must be set to 1 (using the WRCFGA command, see Table

52). The ADCs are off. The reference is powered up so that the

ADBMS1818 can initiate ADC conversions more quickly than from

the standby state.

When a valid ADC command is received, the IC goes to the

measure state to begin the conversion. Otherwise, the ADBMS1818

returns to the standby state when the REFON bit is set to 0, either

manually (using WRCFGA command) or automatically when the

watchdog timer expires (the ADBMS1818 then moves straight into

the sleep state if both timers are expired).

Measure State

The ADBMS1818 performs ADC conversions in the measure state.

The reference and ADCs are powered up.

After ADC conversions complete, the ADBMS1818 transitions to

either the REFUP or standby state, depending on the REFON bit.

Additional ADC conversions can be initiated more quickly by setting

REFON = 1 to take advantage of the REFUP state.

Note that non ADC commands do not cause a core state transition.

Only an ADC conversion or diagnostic commands place the core in

the measure state.

Figure 53. ADBMS1818 Operation State Diagram

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