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

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

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

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.

TEMPERATURE

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

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

WRITE TO

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

WRITE TO

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

WRITE TO

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

Figure 12. One-Shot CT Pin