Datasheet

ADT7316/ADT7317/ADT7318
Rev. B | Page 21 of 44
C1
D+
LOW-PASS
FILTER
f
C
= 65kHz
BIAS
DIODE
V
DD
TO ADC
V
OUT+
V
OUT–
REMOTE
SENSING
TRANSISTOR
(2N3906)
OPTIONAL CAPACITOR, UP TO
3nF MAX. CAN BE ADDED TO
IMPROVE HIGH FREQUENCY
NOISE REJECTION IN NOISY
ENVIRONMENTS
D–
I N × I I
BIAS
02661-041
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
s
ection). 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
V
REF
-AB
2.25V INTERNAL
V
REF
02661-040
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 V
REF
, gain, and offset error.
If a gain of 1 is selected (Bit 0 to Bit 3 = 0, DAC Configuration
r
egister, Address 0x1B), the output range is 0.001 V to V
REF
.
If a gain of 2 is selected (Bit 0 to Bit 3 = 1, DAC Configuration
r
egister, Address 0x1B), the output range is 0.001 V to 2 V
REF
.
Because of clamping, however, the maximum output is limited
to V
DD
– 0.001 V.
The output amplifier is capable of driving a load of 4.7 kΩ to
V
DD
or 4.7 kΩ to GND in parallel with 200 pF to GND (see
Figure 6). The source and sink capabilities of the output
a
mplifier can be seen in Figure 20.
The slew rate is 0.7 V/µs with a half-scale settling time to
±0.5 LS
B (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 b
its. 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 V
REF
-AB, and this can be increased to 0 V to
2 V
REF
-AB. The user can select the internal V
REF
(V
REF
= 2.28 V)
by setting D4 = 1 in the LDAC Configuration register (Address
0x1C). Increasing the output voltage span to 2 V
REF
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-
p
erature 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 V
REF
-AB
(V
REF
-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 V
REF
-AB.
The internal and external analog temperature offset registers
ca
n be used to vary this upper dead band, and consequently,
the temperature that 0 V corresponds to.
Tabl e 6 and Table 7
g
ive examples of how this is done using a DAC output voltage
span of V
REF
and 2 V
REF
, 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.