Datasheet

Data Sheet AD9148
Rev. B | Page 65 of 72
TEMPERATURE SENSOR
The AD9148 has a diode-based temperature sensor for measuring
the temperature of the die. The temperature reading is accessed
by Register 0x5E and Register 0x5F. The temperature of the die
can be calculated as
130
)700,13]0:15[(
−
=
DieTemp
T
DIE
where T
DIE
is the die temperature in degrees Celsius. The
temperature accuracy is ±5°C typical over the +85°C to
−35°C range. A typical plot of the AD9148 die temperature
vs. die temperature code readback is shown in Figure 90.
7,500
–40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100
10,000
12,500
15,000
17,500
20,000
22,500
25,000
27,500
TEMPERATURE (°C)
DIE CODE READBACK
MEASURED DIE TEMPERATURE
CALCULATED DIE TEMPERATURE
+5°C
–5°C
08910-189
Figure 90. Die Temperature vs. Die Temperature Code Readback
Estimates of the ambient temperature can be made if the power
dissipation of the device is known. For example, if the device power
dissipation is 800 mW and the measured die temperature is 50°C,
then the ambient temperature can be calculated as
T
A
= T
DIE
– P
D
× T
JA
= 50 – 0.8 × 18 = 35.6°C
where:
T
A
is the ambient temperature in degrees Celsius.
T
JA
is the thermal resistance from junction to ambient of the
AD9148 as shown in Table 7.
To use the temperature sensor, it must be enabled by setting
Bit 0, Register 0x5C to 0. Before the temperature sensor data
can be read back, it must be latched by toggling Bit 1, Register 0x5C
from 0 to 1. In addition, to get accurate readings, the die temperature
control register (Register 0x5D) should be set to 0x0A.