ALERT RESPONSE ADDRESS
Alert Response Address (ARA) is a feature of SMBus devices
that allows an interrupting device to identify itself to the host
when multiple devices exist on the same bus.
The INT output can be used as an interrupt output or can be used
as an SMBALERT. One or more INT outputs can be connected
to a common SMBALERT line connected to the master. If a
device’s INT line goes low, the following procedure occurs:
1. SMBALERT pulled low.
2. Master initiates a read operation and sends the Alert
Response Address (ARA = 0001 100). This is a general call
address that must not be used as a specific device address.
3. The device whose INT output is low responds to the Alert
Response Address, and the master reads its device address.
The address of the device is now known and can be interro-
gated in the usual way.
4. If more than one device’s INT output is low, the one with
the lowest device address will have priority, in accordance
with normal SMBus arbitration.
5. Once the ADM1030 has responded to the Alert Response
Address, it will reset its INT output; however, if the error
condition that caused the interrupt persists, INT will be
reasserted on the next monitoring cycle.
TEMPERATURE MEASUREMENT SYSTEM
Internal Temperature Measurement
The ADM1030 contains an on-chip bandgap temperature sen-
sor. The on-chip ADC performs conversions on the output of
this sensor and outputs the temperature data in 10-bit two’s
complement format. The resolution of the local temperature
sensor is 0.25∞C. The format of the temperature data is shown
in Table II.
External Temperature Measurement
The ADM1030 can measure the temperature of an external
diode sensor or diode-connected transistor, connected to Pins
9 and 10.
These pins are a dedicated temperature input channel. The
function of Pin 7 is as a THERM input/output and is used to
flag overtemperature conditions.
The forward voltage of a diode or diode-connected transistor,
operated at a constant current, exhibits a negative temperature
coefficient of about –2 mV/∞C. Unfortunately, the absolute
value of VBE, varies from device to device, and individual
calibration is required to null this out, so the technique is
unsuitable for mass production.
The technique used in the ADM1030 is to measure the change
in VBE when the device is operated at two different currents.
This is given by:
DVBE = KT/q ¥ ln (N)
K is Boltzmann’s constant.
q is charge on the carrier.
T is absolute temperature in Kelvins.
N is ratio of the two currents.
Figure 3 shows the input signal conditioning used to measure
the output of an external temperature sensor. This figure shows
the external sensor as a substrate transistor, provided for tempera-
ture monitoring on some microprocessors, but it could equally
well be a discrete transistor.
N ؋ I IBIAS
fC = 65kHz
Figure 3. Signal Conditioning
If a discrete transistor is used, the collector will not be grounded,
and should be linked to the base. If a PNP transistor is used, the
base is connected to the D– input and the emitter to the D+
input. If an NPN transistor is used, the emitter is connected to
the D– input and the base to the D+ input.
One LSB of the ADC corresponds to 0.125∞C, so the ADM1030
can theoretically measure temperatures from –127∞C to +127.75∞C,
although –127∞C is outside the operating range for the device.
The extended temperature resolution data format is shown in
Tables III and IV.
Table II. Temperature Data Format (Local Temperature and
Remote Temperature High Bytes)