Rainbow Electronics MAX1329 - Manual (Page 38)

MAX1329/MAX1330
12-/16-Bit DASs with ADC, DACs, DPIOs, APIOs,
Reference, Voltage Monitors, and Temp Sensor
38 ______________________________________________________________________________________
See Figure 21 for performing an ADC conversion using
a DPIO input programmed as CONVST. Allow at least
600ns for acquisition while the DPIO input is low and
the acquisition ends on the rising edge of the DPIO.
The conversion requires an additional 14 ADC clock
cycles. If the PGA gain is set to 4 or 8, the minimum
acquisition time is 1.2µs due to the increase of the input
sampling capacitor.
Temperature Measurement
The MAX1329/MAX1330 perform temperature measure-
ment by measuring the voltage across a diode-con-
nected transistor at two different current levels. The
following equation illustrates the algorithm used for tem-
perature calculations:
where:
V HIGH = sensor-diode voltage with high current flowing
(I HIGH )
V LOW = sensor-diode voltage with low current flowing
(I LOW )
q = charge of electron = 1.602 ✕ 10 -19 coulombs
k = Boltzman constant = 1.38 ✕ 10 -23 J/K
n = ideality factor (slightly greater than 1)
The temperature measurement process is fully automat-
ed in the MAX1329/MAX1330. All steps are sequenced
and executed by the MAX1329/MAX1330 each time an
input channel (or an input channel pair) configured for
temperature measurement is scanned.
The resulting 12-bit, two’s complement number repre-
sents the sensor temperature in degrees Celsius, with
1 LSB = +0.125°C. Figure 22 shows the timing for a
temperature measurement.
An external 2.500V reference can be applied to
REFADJ, provided the internal reference is disabled
first. Use the temperature correction equation to obtain
the correct temperature:
T ACT = 0.997 x T MEAS - 0.91°C
Use the following equation when using the internal ref-
erence:
T T T
V
V
ACT MEAS MEAS
= + + × − ( . ) (
.
270 63 1
2 500
R REFADJ
C )°
temperature V V x HIGH LOW =
⎡
⎣
⎢
⎤
⎦
⎥
( ) -
q
k
n x ln
I
I
High
LOW
TEMP CONVERT COMMAND
(SCLK, DIN, DOUT NOT SHOWN)
THERE ARE TWO ADC CONVERSIONS PER TEMPERATURE CONVERSION.
1 CLOCK = 1/(ADC MASTER CLOCK FREQUENCY)
ADC MODE TRACK CONVERT TRACK CONVERT
START
CS
STOP
WAIT PERIOD
93.5 CLOCKS 1ST AQUISITION
90 CLOCKS
2ND AQUISITION
87 CLOCKS
2ND CONVERSION
17.5 CLOCKS
1ST CONVERSION
19 CLOCKS
Figure 22. Temperature-Conversion Timing