Datasheet

ADT7316/ADT7317/ADT7318
Rev. B | Page 23 of 44
FUNCTIONAL DESCRIPTION—MEASUREMENT
TEMPERATURE SENSOR
The ADT7316/ADT7317/ADT7318 contain an ADC with spe-
cial input signal conditioning to enable operation with external
and on-chip diode temperature sensors. When the ADT7316/
ADT7317/ADT7318 are operating in single-channel mode, the
ADC continually processes the measurement taken on one
channel only. This channel is preselected by Bit C0 and Bit C1
in the Control Configuration 2 register (Address 0x19). When
in round robin mode, the analog input multiplexer sequentially
selects the V
DD
input channel, the on-chip temperature sensor
to measure its internal temperature, and the external tempera-
ture sensor. These signals are digitized by the ADC and the
results stored in the various value registers.
The measured results are compared with the internal and
ext
ernal, T
HIGH
and T
LOW
, limits. These temperature limits are
stored in on-chip registers. If the temperature limits are not
masked out, any out-of-limit comparisons generate flags that
are stored in the Interrupt Status 1 register (Address 0x00). One
or more out-of-limit results cause the INT/
INT
output to pull
either high or low depending on the output polarity setting.
Theoretically, the temperature measuring circuit can measure
t
emperatures from −128°C to +127°C with a resolution of 0.25°C.
Temperatures outside T
A
, however, are outside the guaranteed
operating temperature range of the device. Temperature meas-
urement from −128°C to +127°C is possible using an external
sensor.
Temperature measurement is initiated by three methods. The first
m
ethod is applicable when the part is in single-channel meas-
urement mode. The temperature is measured 16 times and
internally averaged to reduce noise. In single-channel mode,
the part continuously monitors the selected channel, that is, as
soon as one measurement is taken, then another one is started
on the same channel. The total time to measure a temperature
channel with the ADC operating at slow speed is typically
11.4 ms (712 µs × 16) for the internal temperature sensor, and
24.22 ms (1.51 ms × 16) for the external temperature sensor.
The new temperature value is stored in two 8-bit registers and
ready for reading by the I
2
C or SPI interface. The user can
disable the averaging by setting Bit 5 = 1 in the Control Con-
figuration 2 register (Address 0x19). The ADT7316/ADT7317/
ADT7318 default on power-up, with the averaging enabled.
The second temperature measurement method is applicable
w
hen the part is in round robin measurement mode. The part
measures both the internal and external temperature sensors
as it cycles through all possible measurement channels. The
two temperature channels are measured each time the part
runs a round robin sequence. In round-robin mode, the part
continuously measures all channels.
The third temperature measurement method is initiated after
e
very read or write to the part when the part is in either single-
channel measurement mode or round robin measurement mode.
Once serial communication has started, any conversion in pro-
gress is stopped and the ADC reset. Conversion starts again
immediately after the serial communication has finished. The
temperature measurement proceeds normally as described earlier.
V
DD
MONITORING
The ADT7316/ADT7317/ADT7318 can monitor their own power
supplies. The parts measure the voltage on their V
DD
pin to a
resolution of 10 bits. The resulting value is stored in two 8-bit
registers: the 2 LSBs are stored in the Internal Temperature
Va lue /V
DD
Value register (Address 0x03) and the 8 MSBs are
stored in the V
DD
Value Register MSBs register (Address 0x06).
This allows the user to perform a 1-byte read if 10-bit resolution
is not important. The measured result is compared with V
HIGH
and V
LOW
limits. If the V
DD
interrupt is not masked out, any out-
of-limit comparison generates a flag in the Interrupt Status 2
register (Address 0x10), and one or more out-of-limit results
cause the INT/
INT
output to pull either high or low depending
on the output polarity setting.
Measuring the voltage on the V
DD
pin is regarded as monitoring
a channel. Therefore, along with the internal and external tem-
perature sensors, the V
DD
voltage makes up the third and final
monitoring channel. The user can select the V
DD
channel for
single-channel measurement by setting Bit C4 = 1 and setting
Bit C0 to Bit C2 to all 0s in the Control Configuration 2 register
(Address 0x19).
When measuring the V
DD
value, the reference for the ADC
is sourced from the internal reference. Table 8 shows the data
fo
rmat. As the maximum V
DD
voltage measurable is 7 V,
internal scaling is performed on the V
DD
voltage to match the
2.28 V internal reference value. An example of how the transfer
function works follows.
V
DD
= 5 V
ADC Reference
= 2.28 V
1 LSB = ADC R
eference/2
10
= 2.28/1024 = 2.226 mV
Scale Factor = F
ull-Scale V
CC
/ADC Reference = 7/2.28 = 3.07
Conversion Result = V
DD
/(Scale Factor × LSB Size)
= 5/(3.07 × 2.226 mV)
= 0x2DB