Datasheet
LTC2493
22
2493fd
Figure 11. Equivalent Analog Input Circuit
IINIIN
VV
R
AVG AVG
IN CM REFCM
EQ
+
()
=
()
=
−
•
–
() ()
.05
IIREF
VV V
R
AVG
REFREF CM IN CM
+
()
≈
+
()
15
05
.–
.•
() ()
EEQ
IN
REFEQ
REF
REFCM
V
VR
where
VREF REF
V
–
•
:
(
2
=−
+−
))
–
,
=
=−
+−
+− +
REFREF
VININWHERE IN AN
IN
2
DDINARE THESELECTEDINPUTCHANNELS
V
IN
IN CM
−
+
=
()
––
.
IN
RMINTERNALOSCILLATOR
EQ
−
=
2
2716Ω 00HzMODE
R 2.98MINTERNALOSCILLATOR 50Hz/60
EQ
=Ω HHz MODE
R 0.833 10 /f EXTERNALOSCIL
EQ
12
EOSC
=•
()
LLATOR
IN
+
IN
–
10k
INTERNAL
SWITCH
NETWORK
10k
C
EQ
12µF
10k
I
IN
–
REF
+
I
REF
+
I
IN
+
I
REF
–
2493 F11a
SWITCHING FREQUENCY
f
SW
= 123kHz INTERNAL OSCILLATOR
f
SW
= 0.4 • f
EOSC
EXTERNAL OSCILLATOR
REF
–
10k
100Ω
INPUT
MULTIPLEXER
100Ω
Synchronizing Multiple LTC2493s with a Global
Address Call
In applications where several LTC2493s (or other I
2
C
delta-sigma ADCs from Linear Technology Corporation)
are used on the same I
2
C bus, all converters can be syn-
chronized through the use of a global address call. Prior
to issuing the global address call, all converters must
have completed a conversion cycle. The master then is-
sues a START, followed by the global address 1110111,
and a write request. All converters will be selected and
acknowledge the request. The master then sends a write
byte (optional) followed by the STOP command. This
will update the channel selection (optional) converter
configuration (optional) and simultaneously initiate a start
of conversion for all delta-sigma ADCs on the bus (see
GLOBAL ADDRESS
SCL
SDA
LTC2493 LTC2493 LTC2493…
S W ACK WRITE (OPTIONAL) P
2493 F10
ALL LTC2493s IN SLEEP CONVERSION OF ALL LTC2493s
DATA INPUT
Figure 10. Synchronize Multiple LTC2493s with a Global Address Call
Figure 10). In order to synchronize multiple converters
without changing the channel or configuration, a STOP
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.
Driving the Input and Reference
The input and reference pins of the LTC2493 are connected
directly to a switched capacitor network. Depending on
the relationship between the differential input voltage and
the differential reference voltage, these capacitors are
switched between these four pins. Each time a capacitor
is switched between two of these pins, a small amount
of charge is transferred. A simplified equivalent circuit is
shown in Figure 11.
applicaTions inForMaTion