ltc2493 Linear Technology Corporation, ltc2493 Datasheet - Page 22

• Manufacturer Part Number: ltc2493
• Description: 24-bit 2-/4-channel Delta Sigma Adc With Easy Drive Input Current Cancellation And I2c Interface
• Manufacturer: Linear Technology Corporation

LTC2493
applicaTions inForMaTion
Synchronizing Multiple LTC2493s with a Global
Address Call
In applications where several LTC2493s (or other I
delta-sigma ADCs from Linear Technology Corporation)
are used on the same I
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 issues 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 chan-
nel selection (optional) converter configuration (optional)
and simultaneously initiate a start of conversion for all
delta-sigma ADCs on the bus (see Figure 10). In order

SWITCHING FREQUENCY
f
f
SW
SW
REF
REF
I
I
IN +
IN
I
I
REF
REF
IN
IN
= 123kHz INTERNAL OSCILLATOR
= 0.4 • f
–
+
–
+
–
+
–
EOSC
MULTIPLEXER
INPUT
100Ω
100Ω
EXTERNAL OSCILLATOR
SDA
SCL
2
C bus, all converters can be syn-
S
ALL LTC2493s IN SLEEP
Figure 10. Synchronize Multiple LTC2493s with a Global Address Call
GLOBAL ADDRESS
LTC2493
Figure 11. Equivalent Analog Input Circuit
LTC2493
10kΩ
10kΩ
10kΩ
10kΩ
INTERNAL
NETWORK
W ACK
SWITCH
2
C
WRITE (OPTIONAL)
2493 F11a
DATA INPUT
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
NAK 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.
…
C
12µF
EQ
I IN
I I REF
R
R
R
where
V
V
V
V
( )
( )
REF
REF CM
IN
IN CM
EQ
EQ
EQ
(
+
=
(
=
=
=
=
IN
P
+
:
)
(
AVG
2 71
2.98M INTERNAL OSCILLATOR 50Hz/60
LTC2493
REF
0.833 10
+
=
.
) )
AVG
CONVERSION OF ALL LTC2493s
=




−
=
M INTERNAL OSCILLATOR




IN
+
IN WHERE IN AN
≈
REF
W
I IN
−
W
+
•
−
( )
1 5
REF
,
– –
2
.
–
+
IN
12
V
–
2
REF
−
−
AVG
)
REF




/f
EOSC
+
=
−
(
0 5
V
V
+
. •




IN CM
REF CM
EXTERNAL OSCIL
(
R
. 0 5
(
D D IN ARE THE SELECTED INPUT CHANNELS
E E Q
)
−
)
•
–
V
R
−
REF CM
EQ
V
IN CM
(
(
6
0 0 Hz MODE
2493 F10
)
)
)
L L ATOR
–
V
H H z MODE
REF
V
IN
•
2
R
EQ
2493fa