ltc2428 Linear Technology Corporation, ltc2428 Datasheet - Page 34

• Manufacturer Part Number: ltc2428
• Description: 4-/8-channel 20-bit ?power No Latency Delta-sigma Adc
• Manufacturer: Linear Technology Corporation

APPLICATIONS
LTC2424/LTC2428
could be used to measure the case temperature of the
RTD-based thermal power measurement scheme described
previously. In general, thermistors yield very good resolu-
tion over a limited temperature range. For the half-bridge
arrangement shown, the LTC2428 can measure tempera-
ture changes over nearly 5 orders of magnitude.
Connected to the LTC2428’s CH6 input, an infrared ther-
mocouple (Omega Engineering OS36-1) can be used in
limited range, noncontact temperature measurement ap-
plications or applications where high levels of infrared
light must be measured. Given the LTC2428’s 1.2ppm
noise performance, measurement resolution using infra-
red thermocouples is approximately 0.25 C—equivalent
to the resolution of a conventional Type J thermocouple.
These infrared thermocouples are self-contained: 1) they
do not require external cold junction compensation; 2)
they cannot use conventional open thermocouple detec-
tion schemes; and 3) their output impedances are high,
approximately 3k . Alternatively, conventional thermo-
couples can be connected directly to the LTC2428 (not
shown) and cold junction compensation can be provided
by an external temperature sensor connected to a different
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channel (see the thermistor circuit on CH5) or by using the
LT1025, a monolithic cold-junction compensator IC.
The components connected to CH7 are used to sense
daylight or photodiode current with a resolution of 300pA.
In the figure, the photodiode is biased in photoconduc-
tive mode; however, the LTC2428 can accommodate
either photovoltaic or photoconductive configurations.
The photodiode chosen (Hammatsu S1336-5BK) pro-
duces an output of 500mA per watt of optical illumination.
The output of the photodiode is dependent on two factors:
active detector area (2.4mm • 2.4mm) and illumination
intensity. With the 5k resistor, optical intensities up to
368W/m
1000W/m
resolution of 1nA, the optical dynamic range covers 5
orders of magnitude.
The application circuits shown connected to the LTC2428
demonstrate the mix-and-match capabilities of this multi-
plexed-input, high resolution
signals and high level signals can be accommodated with
a minimum of additional circuitry.
2
2
at 960nM (direct sunlight is approximately
) can be measured by the LTC2428. With a
ADC. Very low level