LTC6820 datasheet(20/92 Pages) AD

20 / 92 page

LTC6811-1/LTC6811-2

Rev. C

For more information www.analog.com

OPERATION

STATE DIAGRAM

The operation of the LTC6811 is divided into two separate

sections: the Core circuit and the isoSPI circuit. Both sec-

tions have an independent set of operating states, as well

as a shutdown timeout.

CORE LTC6811 STATE DESCRIPTIONS

SLEEP State

The references and ADCs are powered down. The watch-

dog timer (see Watchdog and Discharge Timer) has timed

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

The supply currents are reduced to minimum levels. The

isoSPI ports will be in the IDLE state. The Drive pin is 0V.

All state machines are reset to their default states.

If a WAKEUP signal is received (see Waking Up the Serial

Interface), the LTC6811 will enter the STANDBY state.

STANDBY State

The references and the ADCs are off. The watchdog timer

and/or the discharge timer is running. The DRIVE pin

powers the VREG pin to 5V through an external transistor.

(Alternatively,VREGcanbepoweredbyanexternalsupply).

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

set to 1 in the Configuration Register Group, the IC pauses

for tREFUP to allow for the references to power up and then

enters either the REFUP or MEASURE state. Otherwise, if

no valid commands are received for tSLEEP, the IC returns

to the SLEEP state if DTEN = 0 or enters the EXTENDED

BALANCING state if DTEN = 1.

REFUP State

To reach this state the REFON bit in the Configuration

command, see Table 38). The ADCs are off. The references

are powered up so that the LTC6811 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 LTC6811 will return to the STANDBY state when the

REFON bit is set to 0 (using WRCFGA command). If no

valid commands are received for tSLEEP, the IC returns

to the SLEEP state if DTEN = 0 or enters the EXTENDED

BALANCING state if DTEN = 1.

MEASURE State

The LTC6811 performs ADC conversions in this state. The

references and ADCs are powered up.

After ADC conversions are complete, the LTC6811 will

transition to either the REFUP or STANDBY state, depend-

ing on the REFON bit. Additional ADC conversions can

be initiated more quickly by setting REFON = 1 to take

advantage of the REFUP state.

Note: Non-ADC commands do not cause a Core state tran-

sition. Only an ADC conversion or diagnostic commands

will place the Core in the MEASURE state.

68111 F01

isoSPI PORT

CORE LTC6811

CONV DONE

(REFON = 1)

CONV DONE

(REFON = 0)

ADC

COMMAND

WAKEUP

SIGNAL

(tWAKE)

ADC

COMM

(tREFUP)

REFON = 1

(tREFUP)

WAKEUP SIGNAL

(CORE = STANDBY)

(tREADY)

WAKEUP SIGNAL

(CORE = SLEEP)

(tWAKE)

TRANSMIT/RECEIVE

NOTE: STATE TRANSITION

DELAYS DENOTED BY (tX)

NO ACTIVITY ON

isoSPI PORT

IDLE TIMEOUT

(tIDLE)

REFON = 0

WAKEUP SIGNAL

(tWAKE)

DCTO REACHES 0

WD TIMEOUT

AND DTEN=0

(tSLEEP)

WD TIMEOUT

AND DTEN=1

WD TIMEOUT

AND DTEN=1

WD TIMEOUT

AND DTEN=0

(tSLEEP)

STANDBY

REFUP

EXTENDED

BALANCING

MEASURE

SLEEP

ACTIVE

READY

IDLE

Figure 1. LTC6811 Operation State Diagram

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