Datasheet

Data Sheet ADT7420
Rev. 0 | Page 11 of 24
CT and INT Operation in One-Shot Mode
See Figure 12 for more information on one-shot CT pin
operation for T
CRIT
overtemperature events when one of the
limits is exceeded. Note that in interrupt mode, a read from
any register resets the INT and CT pins.
For the INT pin in the comparator mode, if the temperature drops
below the T
HIGH
– T
HYST
value or goes above the T
LOW
+ T
HYST
value, a write to the operation mode bits (Bit 5 and Bit 6 of the
configuration register, Register Address 0x03) resets the INT pin.
For the CT pin in the comparator mode, if the temperature
drops below the T
CRIT
– T
HYST
value, a write to the operation
mode bits (Bit 6 = 0 and Bit 5 = 1 of the configuration register,
Register Address 0x03) resets the CT pin (see Figure 12).
Note that when using one-shot mode, ensure that the refresh
rate is appropriate to the application being used.
1 SPS MODE
In this mode, the part performs one measurement per second.
A conversion takes only 60 ms typically, and it remains in
the idle state for the remaining 940 ms period. This mode is
enabled by writing 1 to Bit 6 and 0 to Bit 5 of the configuration
register (Register Address 0x03).
SHUTDOWN
The ADT7420 can be placed in shutdown mode by writing 1
to Bit 6 and 1 to Bit 5 of the configuration register (Register
Address 0x03), in which case the entire IC is shut down and
no further conversions are initiated until the ADT7420 is
taken out of shutdown mode. The ADT7420 can be taken
out of shutdown mode by writing 0 to Bit 6 and 0 to Bit 5 in
the configuration register (Register Address 0x03). The
ADT7420 typically takes 1 ms (with a 0.1 µF decoupling
capacitor) to come out of shutdown mode. The conversion
result from the last conversion prior to shutdown can still be
read from the ADT7420 even when it is in shutdown mode.
When the part is taken out of shutdown mode, the internal
clock is started and a conversion is initiated.
FAULT QUEUE
Bit 0 and Bit 1 of the configuration register (Register Address
0x03) are used to set up a fault queue. The queue can facilitate up
to four fault events to prevent false tripping of the INT and CT pins
when the ADT7420 is used in a noisy temperature environment.
The number of faults set in the queue must occur consecutively
to set the INT and CT outputs. For example, if the number of
faults set in the queue is four, then four consecutive temperature
conversions must occur with each result exceeding a temperature
limit in any of the limit registers before the INT and CT pins are
activated. If two consecutive temperature conversions exceed a
temperature limit and the third conversion does not, the fault
count is reset back to zero.
TEMPERA
TURE
149°C
148°C
147°C
146°C
145°C
144°C
143°C
142°C
141°C
140°C
CT PIN
POLARITY = ACTIVE LOW
CT PIN
POLARITY = ACTIVE HIGH
T
CRIT
T
CRIT
– T
HYST
TIME
*THERE IS A 240ms DELAY BETWEEN WRITING TO THE CONFIGURATION REGISTER TO START
A STANDARD ONE-SHOT CONVERSION AND THE CT PIN GOING
ACTIVE. THIS IS DUE TO THE
CONVERSION TIME. THE DELAY IS 60ms IN THE CASE OF A ONE-SHOT CONVERSION.
WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATION
REGISTER.*
WRITE T
O
BIT 5 AND BIT 6 OF
CONFIGURATION
REGISTER.*
WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATION
REGISTER.
*
09013-013
Figure 12. One-Shot CT Pin