LTC6804-1/LTC6804-2
20
680412fc
For more information
operaTion
STATE DIAGRAM
The operation of the LTC6804 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.
LTC6804 CORE STATE DESCRIPTIONS
SLEEP State
The reference and ADCs are powered down. The watchdog
timer (see Watchdog and Software Discharge Timer) has
timed out. The software 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.
If a WAKEUP signal is received (see Waking Up the Serial
Interface), the LTC6804 will enter the STANDBY state.
STANDBY State
The reference and the ADCs are off. The watchdog timer
and/or the software discharge timer is running. The DRIVE
pin powers the V
REG
pin to 5V through an external transistor.
(Alternatively, V
REG
can be powered by an external supply).
When a valid ADC command is received or the REFON bit is
set to 1 in the Configuration Register Group, the IC pauses
for t
REFUP
to allow for the reference to power up and then
enters either the REFUP or MEASURE state. If there is no
WAKEUP signal for a duration t
SLEEP
(when both the watch-
dog and software discharge timer have expired) the LTC6804
Figure 1. LTC6804 Operation State Diagram
returns to the SLEEP state. If the software discharge timer
is disabled, only the watchdog timer is relevant.
REFUP State
To reach this state the REFON bit in the Configuration Reg-
ister Group must be set to 1 (using the WRCFG command,
see Table 36). The ADCs are off. The reference is powered
up so that the LTC6804 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
LTC6804 will return to the STANDBY state when the REFON
bit is set to 0, either manually (using WRCFG command)
or automatically when the watchdog timer expires. (The
LTC6804 will then move straight into the SLEEP state if
both timers are expired).
MEASURE State
The LTC6804 performs ADC conversions in this state. The
reference and ADCs are powered up.
After ADC conversions are complete the LTC6804 will
transition to either the REFUP or STANDBY states, de-
pending 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.
680412 F01
isoSPI PORT
CORE LTC6804
CONVERSION DONE
(REFON = 1)
WAKEUP
SIGNAL
(t
WAKE
)
ADC COMMAND
(t
REFUP
)
ADC
COMMAND
REFON = 1
(t
REFUP
)
WAKEUP SIGNAL
(CORE = STANDBY)
(t
READY
)
WAKEUP SIGNAL
(CORE = SLEEP)
(t
WAKE
)
TRANSMIT/RECEIVE
NOTE: STATE TRANSITION
DELAYS DENOTED BY (t
X
)
NO ACTIVITY ON
isoSPI PORT
IDLE TIMEOUT
(t
IDLE
)
CONVERSION
DONE (REFON = 0)
REFON = 0
WD TIMEOUT
OR SWT TIMEOUT
(t
SLEEP
)
MEASURE
REFUP
STANDBY
SLEEP
ACTIVE
READY
IDLE
