AD7416/AD7417/AD7418
Rev. I | Page 17 of 24
OTI OUTPUT
The OTI output has two operating modes that are selected by
Bit D1 of the configuration register. In the comparator mode,
(D1 = 0), the OTI output becomes active when the temperature
exceeds T
OTI
and remains active until the temperature falls
below T
HYST
. This mode allows the AD7416/AD7417/AD7418 to
be used as a thermostat, for example, to control the operation of
a cooling fan.
T
OTI
T
HYST
OTI OUTPUT
COMPARATOR
MODE
OTI OUTPUT
INTERRUPT
MODE
1
IN INTERRUPT MODE, A READ OPERATION OR SHUTDOWN RESETS THE OTI
OUTPUT; OTHERWISE, THE OTI OUTPUT REMAINSACTIVE INDEFINITELY,
ONCE TRIGGERED.
READ
1
READ
1
READ
1
READ
1
READ
1
READ
1
READ
1
01126-019
Figure 20. Operation of OTI Output (Shown Active Low)
The open-drain configuration of OTI allows the OTI outputs of
several AD7416/AD7417/AD7418 devices to be wire-AND’ed
together when in active low mode.
The OTI output is used to indicate that an out-of-limit tempera-
ture excursion has occurred. OTI is an open-drain output that
can be programmed to be active low by setting Bit D2 of the
configuration register to 0 or active high by setting Bit D2 of
the configuration register to 1.
In the interrupt mode (D1 = 1), the OTI output becomes active
when the temperature exceeds T
OTI
and remains active even if
the temperature falls below T
HYST
, until it is reset by a read opera-
tion. Once OTI becomes active by the temperature exceeding
T
OTI
, and resets, it remains inactive even if the temperature
remains, or subsequently rises again, above T
OTI
. It does not
become active again until the temperature falls below T
HYST
. It
then remains active until reset by a read operation. Once OTI
becomes active by the temperature falling below T
HYST
and then
resets, it remains inactive even if the temperature remains, or
subsequently falls again, below T
HYST
.
OTI is also reset when the AD7416/AD7417/AD7418 are placed
in shutdown mode by setting Bit D0 of the configuration
register to 1.
The OTI output requires an external pull-up resistor. This can
be connected to a voltage different from V
DD
(for example, to
allow interfacing between 5 V and 3.3 V systems) provided that
the maximum voltage rating of the OTI output is not exceeded.
The value of the pull-up resistor depends on the application but
should be as large as possible to avoid excessive sink currents at
the OTI output, which can heat the chip and affect the temperature
reading. The maximum value of the pull-up resistor that meets
the output high current specification of the OTI output is 30 kΩ,
but higher values can be used if a lower output current is
required. For most applications, a value of 10 kΩ is suitable.
FAULT QUEUE
To avoid false triggering of the AD7416/AD7417/AD7418 in
noisy environments, a fault queue counter is provided that can
be programmed by Bit D3 and Bit D4 of the configuration
register (see Table 1 1 ) to count 1, 2, 4, or 6 fault events before
OTI becomes active. To trigger OTI, the faults must occur
consecutively. For example, if the fault queue is set to 4, then
four consecutive temperature measurements greater than T
OTI
(or less than T
HYST
) must occur. Any reading that breaks the
sequence resets the fault queue counter, so if there are three
readings greater than T
OTI
followed by a reading less than T
OTI
,
the fault queue counter is reset without triggering OTI.
POWER-ON DEFAULTS
The AD7416/AD7417/AD7418 always power up with the
following defaults:
• Address pointer pointing to temperature value register
comparator mode
• T
OTI
= 80°C
• T
HYST
= 75°C
• OTI active low
• Fault queue = 1
These default settings allow the AD7416/AD7417/AD7418 to
be used as a standalone thermostat without any connection to a
serial bus.
OPERATING MODES
The AD7416/AD7417/AD7418 have two possible modes of
operation depending on the value of D0 in the configuration
register.
Mode 1
Normal operation of the AD7416/AD7417/AD7418 occurs
when D0 = 0. In this active mode, a conversion takes place
every 400 μs. After the conversion has taken place, the part
partially powers down, consuming typically 350 μA of the
current until the next conversion occurs.
Two situations can arise in this mode on the request of a tempera-
ture read. If a read occurs during a conversion, the conversion
aborts and a new one starts on the stop/repeat start condition.
The temperature value that is read is that of the previous com-
pleted conversion. The next conversion typically occurs 400 μs
after the new conversion has begun.
If a read is called between conversions, a conversion is initiated
on the stop/repeat start condition. After this conversion, the
part returns to performing a conversion every 400 μs.
With V
DD
= 3 V for each 400 μs cycle, the AD7416/AD7417/
AD7418 spend 40 μs (or 10% of the time) in conversion mode.
The part spends 360 μs (or 90% of time) in partial power-down
mode. Thus, the average power dissipated by the AD7416/
AD7417/AD7418 is
3 mW × 0.1 + 1 mW × 0.9 = 1.2 mW
