LTC2485 LINER [Linear Technology], LTC2485 Datasheet - Page 14

• 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
Accessing the Special Features of the LTC2485
The LTC2485 combines a high resolution, low noise ∆Σ
analog-to-digital converter with an on-chip selectable tem-
perature sensor, programmable digital filter and output
rate control. These special features are selected through
a single 8-bit serial input word during the data input/out-
put cycle (see Figure 3).
The LTC2485 powers up in a default mode commonly
used for most measurements. The device will remain in
this mode until a valid write cycle is performed. In this
default mode, the measured input is external, the digital
filter simultaneously rejects 50Hz and 60Hz line frequency
noise, and the speed mode is 1x (offset automatically,
continuously calibrated).
The I
functions contained within the LTC2485. In order to
change the mode of operation, a valid write address
followed by 8 bits of data are shifted into the device (see
Table 1). The first 4 bits are reserved and should be low.
The 5th bit (IM) is used to select the internal temperature
sensor as the conversion input, while the 6th and 7th bits
(FA, FB) combine to determine the line frequency rejec-
tion mode. The 8th bit (SPD) is used to double the output
rate by disabling the offset auto calibration.
Temperature Sensor (IM)
The LTC2485 includes an on-chip temperature sensor. The
temperature sensor is selected by setting IM = 1 in the serial
14
SCL
SDA
2
C serial interface grants access to any or all special
START BY
MASTER
U
U
1
7-BIT ADDRESS
2
W
Figure 3. Timing Diagram for Writing to the LTC2485
…
7
SLEEP
U
W
8
LTC2485
ACK BY
9
input data stream. Conversions are performed directly on
the temperature sensor by the converter. While operating
in this mode, the device behaves as a temperature to bits
converter. The digital reading is proportional to the abso-
lute temperature of the device. This feature allows the
converter to linearize temperature sensors or continuously
remove temperature effects from external sensors. Several
applications leveraging this feature are presented in more
detail in the applications section. While operating in this
mode, the speed is set to normal independent of the con-
trol bit (SPD).
Table 1. Selecting Special Modes
1
IM
0
0
0
0
0
0
1
1
1
X
FA
0
0
1
0
0
1
0
0
1
1
2
FB SPD
0
1
0
0
1
0
0
1
0
1
3
X
X
X
0
0
0
1
1
1
0
4
COMMENTS
External Input, 50Hz and 60Hz Rejection,
Autocalibration
External Input, 50Hz Rejection,
Autocalibration
External Input, 60Hz Rejection,
Autocalibration
External Input, 50Hz and 60Hz Rejection,
2x Speed
External Input, 50Hz Rejection, 2x Speed
External Input, 60Hz Rejection, 2x Speed
Temperature Input, 50Hz and 60Hz Rejection,
Autocalibration
Temperature Input, 50Hz Rejection,
Autocalibration
Temperature Input, 60Hz Rejection,
Autocalibration
Reserved, Do Not Use
DATA INPUT
IM
5
FA
6
FB
7
SPD
8
LTC2485
ACK BY
9
2485 F03
2485fa