ADT7518 
 
Rev. A | Page 22 of 40 
WATCHDOG
LIMIT
COMPARISONS
INTERRUPT
MASK
REGISTERS
CONTROL
CONFIGURATION
REGISTER 1
INTERRUPT
STATUS
REGISTER
(TEMP AND
AIN1 TO AIN4)
INTERRUPT
STATUS
REGISTER 2
(V
DD
)
READ RESET
S/W RESET
INTERNAL
TEMP
INT/INT
(LATCHED OUTPUT)
INT/INT
ENABLE BIT
EXTERNAL
TEMP
V
DD
DIODE
FAULT
AIN1AIN4
 
Figure 49. Interrupt Structure
AIN Interrupts 
The measured results from the AIN inputs are compared with 
the AIN VHIGH (greater than comparison) and VLOW (less than or 
equal to comparison) limits. An interrupt occurs if the AIN 
inputs exceed or equal the limit registers. These voltage limits 
are stored in on-chip registers. Note that the limit registers are 
8 bits long while the AIN conversion result is 10 bits long. If the 
voltage limits are not masked out, then any out-of-limit com-
parisons generate flags that are stored in the Interrupt Status 1 
register (Address = 00h) and one or more out-of-limit results 
will cause the INT/INT
 output to pull either high or low 
depending on the output polarity setting. It is good design 
practice to mask out interrupts for channels that are of no 
concern to the application. Figure 49 shows the interrupt 
structure for the ADT7518. It gives a block diagram 
representation of how the various measurement channels affect 
the INT/INT
 pin. 
 
FUNCTIONAL DESCRIPTIONMEASUREMENT 
Temperature Sensor 
The ADT7518 contains an ADC with special input signal 
conditioning to enable operation with external and on-chip 
diode temperature sensors. When the ADT7518 is operating in 
single-channel mode, the ADC continually processes the 
measurement taken on one channel only. This channel is 
preselected by Bits C0:C2 in the Control Configuration 2 
register (Address 19h). When in round robin mode, the analog 
input multiplexer sequentially selects the VDD input channel, the 
on-chip temperature sensor to measure its internal temperature, 
either the external temperature sensor or AIN1 and AIN2, 
AIN3, and then AIN4. These signals are digitized by the ADC 
and the results are stored in the various value registers. 
The measured results from the temperature sensors are com-
pared with the internal and external T
HIGH
, T
LOW
 limits. These 
temperature limits are stored in on-chip registers. If the temp-
erature limits are not masked, any out-of-limit comparisons 
generate flags that are stored in the Interrupt Status 1 register. 
One or more out-of-limit results will cause the INT/INT
 output 
to pull either high or low depending on the output polarity 
setting.  
Theoretically, the temperature measuring circuit can measure 
temperatures from 128癈 to +127癈 with a resolution of 
0.25癈. However, temperatures outside TA are outside the 
guaranteed operating temperature range of the device. Temp-
erature measurement from 128癈 to +127癈 is possible using 
an external sensor. 
Temperature measurement is initiated by three methods. The 
first method is applicable when the part is in single-channel 
measurement mode. The temperature is measured 16 times and 
internally averaged to reduce noise. In single-channel mode, the 
part is continuously monitoring the selected channel, i.e., as 
soon as one measurement is taken 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 祍 ?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 is ready 
for reading by the I
2
C or SPI interface. The user has the option 
of disabling the averaging by setting Bit 5 in the Control 
Configuration 2 register (Address 19h). The ADT7518 defaults 
on power-up with averaging enabled.