ltc2484 Linear Technology Corporation, ltc2484 Datasheet - Page 15

• Manufacturer Part Number: ltc2484
• Description: 24-bit Delta Sigma Adc With Easy Drive Input Current Cancellation
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Temperature Sensor (IM)
The LTC2484 includes an on-chip temperature sensor. The
temperature sensor is selected by setting IM = 1 in the serial
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
absolute 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
control bit SPD.
Rejection Mode (FA, FB)
The LTC2484 includes a high accuracy on-chip oscillator
with no required external components. Coupled with a 4th
order digital lowpass filter, the LTC2484 rejects line fre-
quency noise. In the default mode, the LTC2484 simulta-
neously rejects 50Hz and 60Hz by at least 87dB. The
LTC2484 can also be configured to selectively reject 50Hz
or 60Hz to better than 110dB.
Speed Mode (SPD)
The LTC2484 continuously performs offset calibrations.
Every conversion cycle, two conversions are automati-
cally performed (default) and the results combined. This
result is free from offset and drift. In applications where
the offset is not critical, the autocalibration feature can be
disabled with the benefit of twice the output rate.
U
U
W
U
Linearity, full-scale accuracy, full-scale drift are identical for
both 2x and 1x speed modes. In both the 1x and 2x speed
there is no latency. This enables input steps or multiplexer
channel changes to settle in a single conversion cycle easing
system overhead and increasing the effective conversion
rate.
Output Data Format
The LTC2484 serial output data stream is 32 bits long. The
first 3 bits represent status information indicating the sign
and conversion state. The next 24 bits are the conversion
result, MSB first. The remaining 5 bits are sub LSBs below
the 24-bit level. The third and fourth bit together are also
used to indicate an underrange condition (the differential
input voltage is below –FS) or an overrange condition (the
differential input voltage is above +FS).
CS may be pulled high prior to outputting all
32 bits, aborting the data out transfer and initiating a new
conversion.
Bit 31 (first output bit) is the end of conversion (EOC)
indicator. This bit is available at the SDO pin during the
conversion and sleep states whenever the CS pin is LOW.
This bit is HIGH during the conversion and goes LOW
when the conversion is complete.
Bit 30 (second output bit) is a dummy bit (DMY) and is
always LOW.
Bit 29 (third output bit) is the conversion result sign indi-
cator (SIG). If V
bit is LOW.
IN
is >0, this bit is HIGH. If V
LTC2484
IN
is <0, this
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2484fa