CN-0267

Circuit Note

Rev. B | Page 6 of 8

The results are shown in Table 2 and were measured at the

following conditions:

•

•

ADuCM360 M3 core clock = 2 MHz

•

Both ADCs converting at 50 samples per second

•

ADC0 has both buffers on and gain = 8

•

ADC1 has both buffers on and gain = 16

•

RTD excitation current = 200 µA

•

SPI communicating to AD5421 with serial clock = 100 kHz

•

HART communicating

The circuit with all relevant analog and digital blocks, including

the input sensor, consumes power supply current within the

budget allowed at the minimum 4 mA loop current.

Input Sensor

Voltage T5 to T6

Maximum (mV)

Maximum (mA)

None

24.4

2.44

24PCDFA6D (5 kΩ,

0.66 mA at 3.3 V)

31.0

3.10

In the second method for assessing the circuit power consumption,

the circuit was verified to function as expected with the analog

output current set to the minimum of 4 mA while performing

HART communication. The result showed that the circuit

delivered the 4 mA current and showed no distortion of the

HART output signal.

Primary Sensor Input Performance

The ADuCM360 integrates most of the analog front-end on chip;

therefore, the performance of the analog input is primarily

determined by the specifications of the ADuCM360.

The level of noise is the main factor that can be influenced by

the interaction of the analog front-end with the rest of the

circuitry on the board. Thus, tests were carried out to focus on

the noise and related resolution performance of the system.

The demonstration was configured to transmit data from the

primary analog input, expressed as pressure in kPa, over the

HART communication. One hundred samples were captured,

and a basic data analysis to quantify the performance was

completed. Two of the tests involved the following:

•

The first test was performed with a standard pressure sensor

(Honeywell 24PCDFA6D) soldered directly on the board.

•

A second test was performed with the primary input signal

generated by a set of fixed and variable resistors, as shown

in Figure 7.

Figure 7. Primary Input Signal Generated by a Set of Resistors

ADuCM360

AIN0

1kΩ

27kΩ

10kΩ

18kΩ

1kΩ

0.1µF

0.01µF

0.01µF

AIN1

AVDD

VREF–

GND_SW

VREF+

ADC0