MAX1402EVKIT Maxim Integrated Products, MAX1402EVKIT Datasheet - Page 35

• Manufacturer Part Number: MAX1402EVKIT
• Description: EVAL KIT FOR MAX1402
• Manufacturer: Maxim Integrated Products

Specifications of MAX1402EVKIT

• Number Of Adc's: 1
• Number Of Bits: 18
• Sampling Rate (per Second): 480
• Data Interface: Serial
• Inputs Per Adc: 6 Single Ended
• Input Range: ±VREF/2
• Power (typ) @ Conditions: 26.7mW @ 480SPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: 0°C ~ 70°C
• Utilized Ic / Part: MAX1402
• Interface Type: SMA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: MAX1402

Low power, single-supply operation, and easy interfac-
ing with optocouplers make the MAX1402 ideal for
loop-powered 4–20mA transmitters. Loop-powered
transmitters draw their power from the 4–20mA loop,
limiting the transmitter circuitry to a current budget of
4mA. Tolerances in the loop further limit this current
budget to 3.5mA. Since the MAX1402 consumes only
250µA, a total of 3.25mA remains to power the remain-
ing transmitter circuitry. Figure 18 shows a block dia-
gram for a loop-powered 4–20mA transmitter.
No specific power sequence is required for the
MAX1402; either the V+ or the V
up first. While the latchup performance of the MAX1402
is good, it is important that power be applied to the
MAX1402 before the analog input signals (AIN_) or the
CLKIN inputs, to avoid latchup. If this is not possible,
then the current flow into any of these pins should be
limited to 50mA. If separate supplies are used for the
MAX1402 and the system digital circuitry, then the
MAX1402 should be powered up first.
Figure 18. 4–20mA Transmitter
SENSOR
4–20mA Loop-Powered Transmitters
______________________________________________________________________________________
GND
V+
SPI
4
+5V, 18-Bit, Low-Power, Multichannel,
ISOLATION
BARRIER
SPI
4
DD
Power Supplies
µP/µC
Oversampling (Sigma-Delta) ADC
supply can come
SPI
3
GND
DAC
V+
R
GAIN
Tightly matched 200µA current sources compensate for
errors in 3-wire and 4-wire RTD configurations. In the 3-
wire configuration (Figure 19), the lead resistances
result in errors if only one current source is used. The
200µA will flow through R
between AIN1 and AIN2. An additional current source
compensates for this error by developing an equivalent
voltage across R
AIN1 and AIN2 is not affected by lead resistance. This
assumes both leads are of the same material and of
equal length (R
matching tempcos (5ppm/°C). Both current sources will
flow through R
that will not affect the differential voltage at AIN1 and
AIN2. Using one of the current sources to supply the
reference voltage ensures a more accurate ratiometric
result.
Unlike the 3-wire configuration, the 4-wire configuration
(Figure 20) has no error associated with lead resis-
tances as no current flows in the measurement leads
connected to AIN1 and AIN2. Current source OUT1
provides the excitation current for the RTD and current
source OUT2 provides current to generate the refer-
ence voltage. This reference voltage developed across
R
remains ratiometric to the reference voltage. RTD temp-
co errors in the analog input voltage are due to the tem-
REF
R
R
OFST
FDBK
ensures that the analog input voltage span
C
C
L3
L1
L2
REGULATOR
developing a common-mode voltage
VOLTAGE
= R
ensuring the differential voltage at
L2
) and OUT1 and OUT2 have
L1
R
Y
developing a voltage error
RTD Configurations
3-Wire and 4-Wire
R
R
X
SENSE
4–20mA LOOP
INTERFACE
V
V
IN+
IN-
35