LTC2485 LINER [Linear Technology], LTC2485 Datasheet - Page 18

• Manufacturer Part Number: LTC2485
• Description: 24-Bit ?? ADC with Easy Drive Input Current Cancellation and I2C Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC2485
Discarding a Conversion Result and Initiating a New
Conversion with Optional Configuration Updating
At the conclusion of a conversion cycle, a Write cycle can
be initiated. Once the Write cycle is acknowledged, a stop
(P) command initiates a new conversion. If a new con-
figuration is required, this data can be written into the
device and a stop command initiates a new conversion,
see Figure 8.
Synchronizing Multiple LTC2485s with the Global
Address Call
In applications where several LTC2485s are used on the
same I
global address call. To achieve this, first all the LTC2485s
must have completed the conversion cycle. The master
issues a Start, followed by the LTC2485 global address
1110111 and a Write request. All LTC2485s will be se-
lected and acknowledge the request. The master then
sends the write byte (Optional) and ends the Write opera-
tion with a STOP. This will update the configuration
registers (if a write byte was sent) and initiate a new
conversion simultaneously on all the LTC2485s, as shown
in Figure 9. In order to synchronize the start of conversion
without affecting the configuration registers, the Write
operation can be aborted with a STOP. This initiates a new
conversion on all the LTC2485s without changing the
configuration registers.
18
2
C bus, all LTC2485s can be synchronized with the
SDA
SCL
CONVERSION
U
S
S
7-BIT ADDRESS
ALL LTC2485s IN SLEEP
U
GLOBAL ADDRESS
LTC2485
Figure 8. Start a New Conversion without Reading Old Conversion Result
Figure 9. Synchronize the LTC2485s with the Global Address Call
W
SLEEP
W ACK
LTC2485
W ACK
U
WRITE (OPTIONAL)
DATA INPUT
WRITE (OPTIONAL)
DATA INPUT
Easy Drive Input Current Cancellation
The LTC2485 combines a high precision delta-sigma ADC
with an automatic differential input current cancellation
front end. A proprietary front-end passive sampling
network transparently removes the differential input cur-
rent. This enables external RC networks and high imped-
ance sensors to directly interface to the LTC2485 without
external amplifiers. The remaining common mode input
current is eliminated by either balancing the differential
input impedances or setting the common mode input
equal to the common mode reference (see Automatic
Input Current Cancellation section). This unique architec-
ture does not require on-chip buffers enabling input
signals to swing all the way to ground and up to V
Furthermore, the cancellation does not interfere with the
transparent offset and full-scale auto-calibration and the
absolute accuracy (full scale + offset + linearity) is main-
tained even with external RC networks.
Conversion Clock
A major advantage the delta-sigma converter offers over
conventional type converters is an on-chip digital filter
(commonly implemented as a SINC or Comb filter). For high
resolution, low frequency applications, this filter is typically
designed to reject line frequencies of 50Hz or 60Hz plus their
harmonics. The filter rejection performance is directly re-
lated to the accuracy of the converter system clock. The
…
CONVERSION
P
P
LTC2485
CONVERSION OF ALL LTC2485s
2485 F09
2485 F08
2485fa
CC
.