AD7414 Analog Devices, Inc., AD7414 Datasheet - Page 8

• Manufacturer Part Number: AD7414
• Description: ?0.5c Accurate, 10-bit Digital Temperature Sensors In Sot-23
• Manufacturer: Analog Devices, Inc.

AD7414/AD7415
Figure 7 shows the method the AD7414/AD7415 use to
measure the ambient device temperature. To measure ΔV
the sensor (substrate transistor) is switched between operating
currents of I and N × I. The resulting waveform is passed
through a chopper stabilized amplifier that performs the
functions of amplification and rectification of the waveform to
produce a dc voltage proportional to ΔV
measured by the ADC to give a temperature output in 10-bit,
twos complement format.
TEMPERATURE DATA FORMAT
The temperature resolution of the ADC is 0.25°C, which
corresponds to 1 LSB of the ADC. The ADC can theoretically
measure a temperature span of 255°C; the lowest practical value
is limited to −40°C due to the device maximum ratings. The
A grade can measure a temperature range of −40°C to +125°C.
(Temperature data format is shown in Table 5.)
TRANSISTOR
SENSING
I
Figure 7. Temperature Measurement Technique
SENSING
TRANSISTOR
I × N
V
DD
BE
. This voltage is
V
V
TO ADC
OUT
OUT
BE
,
+
–
Rev. E | Page 8 of 20
Table 5. A Grade Temperature Data Format
Temperature
−55°C
−50°C
−25°C
−0.25°C
0°C
+0.25°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
The grade temperature conversion formula follows:
Note that DB9 is removed from the ADC code in the negative
temperature formula.
Positive
Negative
Temperatur
Temperatur
Digital Output DB9…DB0
11 0010 0100
11 0011 1000
11 1001 1100
11 1111 1111
00 0000 0000
00 0000 0001
00 0010 1000
00 0110 0100
00 1100 1000
01 0010 1100
01 1001 0000
01 1111 0100
e
e
=
=
ADC
ADC
Code
4
Code
4
(d
(
d
)
)
−
512