Datasheet

LTC2309
18
2309fd
AppLICAtIOns InFORMAtIOn
Synchronizing Multiple LTC2309s with a Global
Address Call
In applications where several LTC2309s or other I
2
C SAR
ADCs from Linear Technology Corporation are used on
the same I
2
C bus, all converters can be synchronized
through the use of a global address call. Prior to issu-
ing the global address call, all converters must have
completed a conversion cycle. The master then issues
a START, followed by the global address 1101011, and
a write request. All converters will be selected and ac-
knowledge the request. The master then sends a write
byte (optional) followed by the STOP command. This will
update the channel selection (optional) and simultane-
ously initiate a conversion for all ADCs on the bus (see
Figure 11). In order to synchronize multiple converters
without changing the channel, a STOP command may
be issued after acknowledgement of the global write
command. Global read commands are not allowed and
the converters will NACK a global read request.
Nap Mode
The ADC enters nap mode after a conversion is com-
plete (t
CONV
) if the SLP bit is set to a logic 0. The sup-
ply current decreases to 210μA in nap mode between
conversions, thereby reducing the average power
dissipation as the sample rate decreases. For example,
the LTC2309 draws an average of 300µA at a 1ksps
sampling rate. The LTC2309 keeps only the reference
(V
REF
) and reference buffer (REFCOMP) circuitry active
when in nap mode.
Sleep Mode
The ADC enters sleep mode after a conversion is com-
plete (t
CONV
) if the SLP bit is set to a logic 1. The ADC
draws only 7µA in sleep mode, provided that none of
the digital inputs are switching. When the LTC2309 is
properly addressed, the ADC is released from sleep mode
and requires 200ms (t
REFWAKE
) to wake up and charge
the respective 2.2μF and 10μF bypass capacitors on the
V
REF
and REFCOMP pins. A new conversion should not
be initiated before this time, as shown in Figure 12.
S
SDA
SCL
CONVERSION NAP
LTC2309
DATA OUTPUT CONVERSION OF ALL LTC2309s
W ACK WRITE (OPTIONAL)GLOBAL ADDRESS P
LTC2309 LTC2309
2309 F11
Figure 11. Synchronous Multiple LTC2309s with a Global Address Call
S
CONVERSION SLEEP t
REFWAKE
CONVERSION
R/W ACK7-BIT ADDRESS P
2309 F12
Figure 12. Exiting Sleep Mode and Starting a New Conversion