ADFS7124-8BBCPZ datasheet(72/93 Pages) AD

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Data Sheet

ADFS7124-8

DIAGNOSTICS

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Rev. 0 | 72 of 93

BURNOUT CURRENTS

The ADFS7124-8 contains two constant current generators that can

be programmed to 0.5 µA, 2 µA, or 4 µA. One generator sources

current from AVDD to AINP, and one sinks current from AINM to

AVSS. These currents enable open wire detection.

X-MUX

AVDD

AVSS

BURNOUT

DETECT

PGA1

Figure 124. Burnout Currents

The currents are switched to the selected analog input pair. Both

currents are either on or off. The burnout bits in the configuration

amplitude. Use these currents to verify that an external transducer

is still operational before attempting to take measurements on that

channel. After the burnout currents are turned on, they flow in

the external transducer circuit, and a measurement of the input

voltage on the analog input channel can be taken. If the resulting

voltage measured is near full scale, verify why this is the case. A

near full-scale reading can mean that the front-end sensor is open

circuit. It can also mean that the front-end sensor is overloaded

and is justified in outputting full scale, or that the reference may be

absent and the REF_DET_ERR bit is set, thus clamping the data to

all 1s.

When a conversion is close to full scale, check these three cases

before making a judgment. If the voltage measured is 0 V, it may in-

dicate that the transducer has short circuited. For normal operation,

these burnout currents are turned off by setting the burnout bits

to zero. The current sources work over the normal absolute input

voltage range specifications with buffers on.

TEMPERATURE SENSOR

The ADFS7124-8 has an embedded temperature sensor useful to

monitor the die temperature. This is selected using the AINP[4:0]

and AINM[4:0] bits in the channel register. Thus, the analog input is

Temperature Sensor – AVSS. Because AINM is connected to AVSS

for the measurement, the AINM_UV_ERR flag may be set when

the internal temperature measurement is being performed if the

flag is enabled. Therefore, ignore the AINM_UV_ERR flag for the

temperature sensor measurement.

The sensitivity is 13,584 codes/°C, approximately. The equation for

the temperature sensor is:

Temperature (°C) = ((Conversion − 0x800000)/13,584) − 272.5

The temperature sensor has an accuracy of ±0.5°C typically.

–0.6

–0.4

–0.2

0.2

0.4

0.6

0.8

1.0

1.2

–40 –30 –20 –10 0

15 25 40 50 60 70 85 95 105 115 125

TEMPERATURE (°C)

32 UNITS

Figure 125. Temperature Sensor Error vs. Temperature

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