AD9689-2000EBZ datasheet(36/134 Pages) AD

36 / 134 page

AD9689

Data Sheet

Rev. A | Page 36 of 134

The temperature diode voltages can be exported to the VREF pin

using the SPI. Use Register 0x18E6 to enable or disable diodes.

It is important to note that other voltages may be exported to

the VREF pin at the same time, which may result in undefined

behavior. To ensure a proper readout, switch off all other voltage

exporting circuits as described in this section. Figure 98 shows

the block diagram of the controls that are required to enable the

diode voltage readout.

TEMPERATURE DIODE

LOCATION SELECT

SPI REGISTER (0x18E6)

VREF PIN

CONTROL

SPI REGISTER

(0x18A6)

CHANNEL A

CENTRAL

VREF

CHANNEL B

Figure 98. Register Controls to Output Temperature Diode Voltage on the

VREF Pin

The SPI writes required to export the central temperature diode

are as follows (see Table 46 and Table 53 for more information):

Set Register 0x0008 to 0x03 to select both channels.

Set Register 0x18E3 to 0x00 to turn off VCM export.

Set Register 0x18A6 to 0x00 to turn off voltage reference

export.

Set Register 0x18E6 to 0x01 to turn on voltage export of

the central 1× temperature diode. The typical voltage

response of the temperature diode is shown in Figure 99.

Although this voltage represents the die temperature, it is

recommended to take measurements from a pair of diodes

for improved accuracy. Step 5 explains how to enable the

20× diode.

Set Register 0x18E6 to 0x02 to turn on the second central

temperature diode of the pair, which is 20× the size of the

first. For the method using two diodes simultaneously to

achieve a more accurate result, see the AN-1432 Application

Note.

0.80

0.75

0.70

0.65

0.60

0.55

0.50

–40

–20

JUNCTION TEMPERATURE (°C)

100

Figure 99. Typical Voltage Response of the 1× Temperature Diode

The relationship between the measured delta voltage (ΔV) and

the junction temperature in °C is shown in Figure 100.

150

–40

–30

–20

–10

100

110

120

130

140

100

105

110

DELTA VOLTAGE (mV)

Figure 100. Junction Temperature vs. ΔV (mV)

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