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AD9208

Data Sheet

Rev. 0 | Page 32 of 136

ADC

DIGITAL

VREF

JESD204B DRIVER

TEMPERATURE DIODE

LOCATIONS

CHANNEL A, CENTRAL,

CHANNEL B

Figure 72. Temperature Diode Locations in the Die

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 can result in undefined

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

exporting circuits as described in this section. Figure 73 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 73. 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 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 74.

Although this voltage represents the die temperature, it is

recommended to take measurements from a pair of diodes

for improved accuracy. The following step 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, Practical Thermal Modeling and Measurements in

High Power ICs.

0.80

0.75

0.70

0.65

0.60

0.55

0.50

–40

–20

JUNCTION TEMPERATURE (°C)

100

Figure 74. 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 75.

150

–40

–30

–20

–10

100

110

120

130

140

100

105

110

DELTA VOLTAGE (mV)

Figure 75. Junction Temperature vs. ΔV (mV)

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