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ADT7317ARQ
(Rev.:RevPrN)

SPI/I2C® Compatible, 10-Bit Digital Temperature Sensor and Quad Voltage Output 12/10/8-Bit DAC

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADT7316/7317/7318

nominal value by the time 50ms has elasped then it is

R

recommended that a measurement be taken on the VDD

channel before a temperature measurement is taken.

R

R

TO OUTPUT

AMPLIFIER

R

R

Figure 9. Resistor String

If there is a buffered reference in the circuit , there is no

need to use the on-chip buffers. In unbuffered mode the

input impedance is still large at typically 90 kΩ per refer-

ence input for 0-VREF output mode and 45 kΩ for 0-2VREF

output mode.

The buffered/unbuffered option is controlled by the DAC

Configuration Register (address 1Bh, see data register

descriptions). The LDAC Configuration register controls

the option to select between internal and external voltage

references. The default setting is for external reference

selected.

Output Amplifier

The output buffer amplifier is capable of generating out-

put voltages to within 1mV of either rail. Its actual range

depends on the value of VREF, GAIN and offset error.

If a gain of 1 is selected (Bits 0-3 of DAC Configuration

register = 0) the output range is 0.001 V to VREF.

If a gain of 2 is selected (Bits 0-3 of DAC Configuration

register = 1) the output range is 0.001 V to 2VREF. How-

ever because of clamping the maximum output is limited

to VDD - 0.001V.

The output amplifier is capable of driving a load of 2kΩ

to GND or VDD, in parallel with 500pF to GND or VDD.

The source and sink capabilities of the output amplifier

can be seen in the plot in TPC 11.

The slew rate is 0.7V/µs with a half-scale settling time to

+/-0.5 LSB (at 8 bits) of 6µs.

FUNCTIONAL DESCRIPTION

POWER-UP TIME

On power-up it is important that no communication to the

part is initiated until 200ms after Vcc has settled. During

this 200ms the part is performing a calibration routine and

any communication to the device will interrupt this rou-

tine and could cause erroneous temperature measurements.

VDD must have settled to within 10% of it’s final value

after 50ms power-on time has elasped. Therefore once

power is applied to the ADT7316/17/18, it can be ad-

dressed 250ms later. If it not possible to have VDD at it’s

TEMPERATURE SENSOR

The ADT7316/7317/7318 contains a two-channel A to D

converter with special input signal conditioning to enable

operation with external and on-chip diode temperature

sensors. When the ADT7316/7317/7318 is operating nor-

mally, the A to D converter operates in a free-running

mode. When in Round Robin mode the analog input mul-

tiplexer sequently selects the VDD input channel, on-chip

temperature sensor to measure its internal temperature and

then the external temperature sensor. These signals are

digitized by the ADC and the results stored in the various

Value Registers.

The measured results are compared with the Internal and

External, THIGH, TLOW limits. These temperature limits are

stored in on-chip registers. If the temperature limits are

not masked out then any out of limit comparisons generate

flags that are stored in Interrupt Status 1 Register and one

or more out-of limit results will cause the INTERRUPT

output to pull either high or low depending on the output

polarity setting.

Theoretically, the temperature sensor and ADC can mea-

sure temperatures from -128oC to +127oC with a resolu-

tion of 0.25oC. However, temperatures outside TA are

outside the guaranteed operating temperature range of the

device. Temperature measurement from -128oC to

+127oC is possible using an external sensor.

Temperature measurement is initiated by three methods.

The first method is applicable when the part is in single

channel measurement mode. It uses an internal clock

countdown of 20ms and then a conversion is preformed.

The internal oscillator is the only circuit that’s powered

up between conversions and once it times out, every 20ms,

a wake-up signal is sent to power-up the rest of the cir-

cuitry. A monostable is activated at the beginning of the

wake-up signal to ensure that sufficient time is given to

the power-up process. The monostable typically takes 4 µs

to time out. It then takes typically 25µs for each conver-

sion to be completed. The temperature is measured 16

times and internally averaged to reduce noise. The total

time to measure a temperature channel is typically 400us

(25us x 16). The new temperature value is loaded into the

Temperature Value Register and ready for reading by the

I2C or SPI interface. The user has the option of disabling

the averaging by setting a bit (Bit 5) in the Control Con-

figuration Register 2 (address 19h). The ADT7316/7317/

7318 defaults on power-up with the averaging enabled.

Temperature measurement is also initiated after every read

or write to the part when the part is in single channel mea-

surement mode. Once serial communication has started,

any conversion in progress is stopped and the ADC reset.

Conversion will start again immediately after the serial

communication has finished. The temperature measure-

ment proceeds normally as described above.

The third method is applicable when the part is in round

robin measurement mode. The part measures both the

–14–

REV. PrN

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