ADT7411ARQZ10 View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

ADT7411ARQZ10

SPI®/I2C® Compatible, 10-Bit Digital Temperature Sensor and 8-Channel ADC

Analog Devices 

ADC Transfer Function

The output coding of the ADT7411 analog inputs is straight

binary. The designed code transitions occur midway between

successive integer LSB values (i.e., 1/2 LSB, 3/2 LSB). The LSB is

VDD/1024 or Int VREF/1024, Int VREF = 2.25 V. The ideal transfer

characteristic is shown in Figure 24.

111...111

111...110

111...000

011...111

000...010

000...001

000...000

0V 1/2 LSB

1LSB = INT VREF/1024

1LSB = VDD/1024

+VREF – 1LSB

ANALOG INPUT

Figure 24. Transfer Function

To work out the voltage on any analog input channel, the

following method can be used:

1 LSB = Reference (V ) 1024

Convert the value read back from the AIN value register into

decimal.

AINVoltage = AINValue(d) × LSB size

where d = decimal

Example:

Internal reference used. Therefore, VREF = 2.25 V.

AIN value = 512d

1 LSB size = 2.25 V 1024 = 2.197 × 10−3

AINVoltage = 512 × 2.197 × 10−3

= 1.125V

Analog Input ESD Protection

Figure 26 shows the input structure that provides ESD protec-

tion on any of the analog input pins. The diode provides the

main ESD protection for the analog inputs. Care must be taken

that the analog input signal never drops below the GND rail by

more than 200 mV. If this happens, the diode will become

forward biased and start conducting current into the substrate.

The 4 pF capacitor is the typical pin capacitance and the resistor

is a lumped component made up of the on resistance of the

multiplexer switch.

VDD

I

N×I

IBIAS

ADT7411

INTERNAL

SENSE

TRANSISTOR

BIAS

DIODE

VOUT+

TO ADC

VOUT–

Figure 25. Top Level Structure of Internal Temperature Sensor

AIN

4pF

100Ω

Figure 26. Equivalent Analog Input ESD Circuit

AIN Interrupts

The measured results from the AIN inputs are compared with

the AIN VHIGH (greater than comparison) and VLOW (less than or

equal to comparison) limits. An interrupt occurs if the AIN

inputs exceed or equal the limit registers. These voltage limits

are stored in on-chip registers. Note that the limit registers are

eight bits long while the AIN conversion result is 10 bits long.

If the voltage limits are not masked out, any out-of-limit

comparisons generate flags that are stored in the Interrupt

Status 1 register (Address 00h) and one or more out-of-limit

results will cause the INT/INT output to pull either high or low,

depending on the output polarity setting. It is good design prac-

tice to mask out interrupts for channels that are of no concern

to the application. Figure 27 shows the interrupt structure for

the ADT7411. It shows a block diagram representation of how

the various measurement channels affect the INT/INT pin.

FUNCTIONAL DESCRIPTION—MEASUREMENT

Temperature Sensor

The ADT7411 contains an A/D converter with special input

signal conditioning to enable operation with external and on-

chip diode temperature sensors. When the ADT7411 is oper-

ating in single-channel mode, the A/D converter continually

processes the measurement taken on one channel only. This

channel is preselected by bits C0:C3 in the Control Config-

uration 2 register (Address 19h). When in round robin mode

the analog input multiplexer sequentially selects the VDD input

channel, on-chip temperature sensor to measure its internal

temperature, the external temperature sensor, or an AIN

channel, and then the rest of the AIN channels. These signals

are digitized by the ADC and the results stored in the various

value registers.

Rev. A | Page 15 of 36

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