MAX1407 Datasheet, PDF (44/48 Pages) Maxim Integrated Products – Low-Power, 16-Bit Multichannel DAS with Internal Reference,10-Bit DACs, and RTC

Low-Power, 16-Bit Multichannel DAS with
Internal Reference,10-Bit DACs, and RTC
REF
R_L
IN0
8:1
MUX
R_T
AGND
8:1
MUX
REF
16b ADC
CMP
WAKE-UP
INTERRUPT
GENERATOR
MAX1407
MAX1408
MAX1409
MAX1414
BAND
GAP
BUF
DRDY NOT AVAILABLE ON THE MAX1409
Figure 27. Thermistor Application Circuit
DRDY
INT
REF
4.7µF
CJC
THERMOCOUPLE
JUNCTION
R
IN0
8:1
MUX
C ^IN1
R
AGND
8:1
MUX
C ^IN2
4.7µF
REF
BUF
BAND
GAP
REF
16b ADC
CMP
WAKE-UP
INTERRUPT
GENERATOR
MAX1407
MAX1408
MAX1414
DRDY
INT
Figure 28. Thermocouple Application Circuit
maintain the reference electrode bias voltage by virtue of
the feedback path through the sensor.
Optical Reflectometry
Figure 26 illustrates the MAX1407/MAX1414 in an optical
reflectometry application. The first DAC is used with an
external transistor to set the bias current through the LED
and the second DAC is used to properly bias and convert
the photodiode current to a voltage measured by the
ADC. The low input bias current into the DAC feedback
pin (FB2) allows the measurement of very small currents.
The DACs provide the flexibility in setting an accurate
and stable LED current and adjusting the bias across the
photodiode. Set the LED bias current externally if the
MAX1409 is used in this application.
Thermistor Measurement
A thermistor connected in a half-bridge configuration
as shown in Figure 27 is used to measure temperatures
very accurately with the MAX1407/MAX1408/
MAX1409/MAX1414. The internal reference drives the
thermistor as well as the ADC, so the reference varia-
tion is cancelled out when calculating the temperature.
The only significant errors are from the R_L resistor and
the thermistor itself. The ADC performs a unipolar con-
version with the PGA set to a gain of 1V/V.
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