LTC2497_15 Datasheet, PDF (19/30 Pages) Linear Technology – 16-Bit 8-/16-Channel ADC with Easy Drive Input Current Cancellation and I2C Interface

LTC2497
Applications Information
Synchronizing Multiple LTC2497s with a Global
Address Call
In applications where several LTC2497s (or other I²C delta-
sigma ADCs from Linear Technology Corporation) are used
on the same I²C bus, all converters can be synchronized
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 channel selection
(optional) and simultaneously initiate a start of conversion
for all delta-sigma ADCs on the bus (see Figure 8). In order
to synchronize multiple converters without changing the
channel, 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 LTC2497 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 9.
When using the LTC2497’s internal oscillator, the input
capacitor array is switched at 123kHz. The effect of the
charge transfer depends on the circuitry driving the input/
reference pins. If the total external RC time constant is less
than 580ns the errors introduced by the sampling process
are negligible since complete settling occurs.
SCL
SDA
LTC2497
LTC2497
…
LTC2497
S GLOBAL ADDRESS W ACK WRITE (OPTIONAL) P
ALL LTC2497s IN SLEEP
DATA INPUT
CONVERSION OF ALL LTC2497s
2497 F08
Figure 8. Synchronize Multiple LTC2497s with a Global Address Call
For more information www.linear.com/LTC2497
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