ADM1032
seven bits, an LSB of 1 is added. The address of
the device is now known, and it can be
interrogated in the usual way.
4. If more than one device’s ALERT output is low,
the one with the lowest device address has priority
in accordance with normal SMBus arbitration.
5. Once the ADM1032 has responded to the alert
response address, it resets its ALERT output,
provided that the error condition that caused the
ALERT no longer exists. If the SMBALERT line
remains low, the master sends ARA again, and so
on until all devices whose ALERT outputs were
low have responded.
Low Power Standby Mode
2. If the local or remote temperature continues to
increase and either one exceeds the THERM limit,
the THERM output asserts low. This can be used
to throttle the CPU clock or switch on a fan.
A THERM hysteresis value is provided to prevent a
cooling fan cycling on and off. The power-on default value
is 10C, but this can be reprogrammed to any value after
powerup. This hysteresis value applies to both the local and
remote channels.
Using these two limits in this way, allows the user to gain
maximum performance from the system by only slowing it
down should it be at a critical temperature.
The THERM signal is open drain and requires a pullup to
V
DD
. The THERM signal must always be pulled up to the
same power supply as the ADM1032, unlike the SMBus
signals (SDATA, SCLK, and ALERT) that can be pulled to
a different power rail, usually that of the SMBus controller.
100C
90C
80C
70C
60C
50C
40C
THERM
TEMPERATURE
LOCAL THERM LIMIT
LOCAL THERM LIMIT
−
HYSTERESIS
The ADM1032 can be put into a low power standby mode
by setting Bit 6 of the configuration register. When Bit 6 is
low, the ADM1032 operates normally. When Bit 6 is high,
the ADC is inhibited and any conversion in progress is
terminated without writing the result to the corresponding
value register.
The SMBus is still enabled. Power consumption in the
standby mode is reduced to less than 10
mA
if there is no
SMBus activity, or 100
mA
if there are clock and data signals
on the bus.
When the device is in standby mode, it is still possible to
initiate a one-shot conversion of both channels by writing
XXh to the one-shot register (Address 0Fh), after which the
device returns to standby. It is also possible to write new
values to the limit register while it is in standby. If the values
stored in the temperature value registers are now outside the
new limits, an ALERT is generated even though the
ADM1032 is still in standby.
The ADM1032 Interrupt System
Figure 17. Operation of the THERM Output
Table 13. THERM HYSTERESIS SAMPLE VALUES
THERM Hysteresis
0C
1C
10C
Binary Representation
0 000 0000
0 000 0001
0 000 1010
The ADM1032 has two interrupt outputs, ALERT and
THERM. These have different functions. ALERT responds
to violations of software-programmed temperature limits
and is maskable. THERM is intended as a fail-safe interrupt
output that cannot be masked.
If the temperature goes equal to or below the lower
temperature limit, the ALERT pin is asserted low to indicate
an out-of-limit condition. If the temperature is within the
programmed low and high temperature limits, no interrupt
is generated.
If the temperature exceeds the high temperature limit, the
ALERT pin is asserted low to indicate an overtemperature
condition. A local and remote THERM limit can be
programmed into the device to set the temperature limit
above which the overtemperature THERM pin is asserted
low. This temperature limit should be equal to or greater than
the high temperature limit programmed.
The behavior of the high limit and THERM limit is as
follows:
1. If either temperature measured exceeds the high
temperature limit, the ALERT output is asserted
low.
Sensor Fault Detection
At the D+ input, the ADM1032 has a fault detector that
detects if the external sensor diode is open circuit. This is a
simple voltage comparator that trips if the voltage at D+
exceeds V
DD
−
1.0 V (typical). The output of this
comparator is checked when a conversion is initiated and
sets Bit 2 of the status register if a fault is detected.
If the remote sensor voltage falls below the normal
measuring range, for example, due to the diode being
short-circuited, the ADC outputs
−128
(1000 0000). Since
the normal operating temperature range of the device only
extends down to 0C, this output code should never be seen
in normal operation, so it can be interpreted as a fault
condition. Since it is outside the power-on default low
temperature limit (0C) and any low limit that would
normally be programmed, a short-circuit sensor causes an
SMBus alert.
http://onsemi.com
13
ONSEMI [ ON SEMICONDUCTOR ]
