ADT7316ARQZ datasheet(21/44 Pages) AD

21 / 44 page

ADT7316/ADT7317/ADT7318

Rev. B | Page 21 of 44

D+

LOW-PASS

FILTER

fC = 65kHz

BIAS

DIODE

VDD

TO ADC

VOUT+

VOUT–

REMOTE

SENSING

TRANSISTOR

(2N3906)

OPTIONAL CAPACITOR, UP TO

3nF MAX. CAN BE ADDED TO

IMPROVE HIGH FREQUENCY

NOISE REJECTION IN NOISY

ENVIRONMENTS

D–

N × I

IBIAS

Figure 41. Signal Conditioning for External Diode Temperature Sensors

The buffered/unbuffered option is controlled by the DAC

Configuration register (Address 0x1B; see the Registers

section). The LDAC Configuration register controls the

selection between internal and external voltage references.

The default setting is for external reference to be selected.

STRING

DAC A

STRING

DAC B

VREF-AB

2.25V INTERNAL

VREF

Figure 42. DAC Reference Buffer Circuit

OUTPUT AMPLIFIER

The output buffer amplifier is capable of generating output

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

on the value of VREF, gain, and offset error.

If a gain of 1 is selected (Bit 0 to Bit 3 = 0, DAC Configuration

If a gain of 2 is selected (Bit 0 to Bit 3 = 1, DAC Configuration

Because of clamping, however, the maximum output is limited

to VDD – 0.001 V.

The output amplifier is capable of driving a load of 4.7 kΩ to

VDD or 4.7 kΩ to GND in parallel with 200 pF to GND (see

Figure 6). The source and sink capabilities of the output

amplifier can be seen in Figure 20.

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

±0.5 LSB (at 8 bits) of 6 μs.

THERMAL VOLTAGE OUTPUT

The ADT7316/ADT7317/ADT7318 are capable of outputting

voltages that are proportional to temperature. The DAC A

output can be configured to represent the temperature of the

internal sensor while DAC B output can be configured to

represent the external temperature sensor. Bit C5 and Bit C6

of the Control Configuration 3 register select the temperature

proportional to output voltage. Each time a temperature

measurement is taken, the DAC output is updated. The out-

put resolution for the ADT7318 is 8 bits with the 1°C change

corresponding to the 1 LSB change. The output resolution for

the ADT7316 and ADT7317 is capable of 10 bits with a 0.25°C

change corresponding to the 1 LSB change.

The default output resolution for the ADT7316 and ADT7317

is 8 bits. To increase this to 10 bits, set C1 = 1 of the Control

Configuration 3 register (Address 0x1A). The default output

range is 0 V to VREF-AB, and this can be increased to 0 V to

2 VREF-AB. The user can select the internal VREF (VREF = 2.28 V)

by setting D4 = 1 in the LDAC Configuration register (Address

0x1C). Increasing the output voltage span to 2 VREF can be done

by setting D0 = 1 for DAC A (internal temperature sensor), and

D1 = 1 for DAC B (external temperature sensor) in the DAC

Configuration register (Address 0x1B).

The output voltage is capable of tracking a maximum tem-

perature range of −128°C to +127°C, but the default setting is

−40°C to +127°C. If the output voltage range is 0 V to VREF-AB

(VREF-AB = 2.25 V), then this corresponds to 0 V representing

−40°C, and 1.48 V representing +127°C. This gives an upper

dead band between 1.48 V and VREF-AB.

The internal and external analog temperature offset registers

can be used to vary this upper dead band, and consequently,

the temperature that 0 V corresponds to. Table 6 and Table 7

give examples of how this is done using a DAC output voltage

span of VREF and 2 VREF, respectively. Write in the temperature

value, in twos complement format, at which 0 V is to start. For

example, if using the DAC A output with 0 V to start at −40°C,

program 0xD8 into the internal analog temperature offset regis-

ter (Address 0x21). This is an 8-bit register, and thus, only has a

temperature offset resolution of 1°C for all device models. Use

the following formulas to determine the value to program into

the offset registers.

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