M
Unused Diode Channels
If one or more of the remote-diode channels is not
needed, short the DXP and DXN pins for that channel
together. The status register indicates a diode “fault”
for this channel and the channel is ignored during the
temperature-measurement sequence.
Thermal Mass and Self-Heating
When sensing local temperature, the MAX6689 mea-
sures the temperature of the PC board to which it is sol-
dered. The leads provide a good thermal path between
the PC board traces and the die. As with all IC temper-
ature sensors, thermal conductivity between the die
and the ambient air is poor by comparison, making air
temperature measurements impractical. Because the
thermal mass of the PC board is far greater than that of
the MAX6689, the device follows temperature changes
on the PC board with little or no perceivable delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtu-
ally no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote
transistors, the best thermal response times are
obtained with transistors in small packages (i.e., SOT23
or SC70). Take care to account for thermal gradients
between the heat source and the sensor, and ensure
that stray air currents across the sensor package do
not interfere with measurement accuracy. Self-heating
does not significantly affect measurement accuracy.
Remote-sensor self-heating due to the diode current
source is negligible.
7-Channel Precision Temperature Monitor
14
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Table 7. Status 1 Register
BIT
NAME
POR
STATE
FUNCTION
7 (MSB)
Reserved
0
—
6
Local ALERT
0
Local Channel High-Alert Bit. This bit is set to logic 1 when the local
temperature exceeds the temperature threshold limit in the local ALERT high-
limit register.
5
Remote 6 ALERT
0
Channel 6 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 6 remote-diode temperature exceeds the temperature threshold limit
in the remote 6 ALERT high-limit register.
4
Remote 5 ALERT
0
Channel 5 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 5 remote-diode temperature exceeds the programmed temperature
threshold limit in the remote 5 ALERT high-limit register.
3
Remote 4 ALERT
0
Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 4 remote-diode temperature exceeds the temperature threshold limit
in the remote 4 ALERT high-limit register.
2
Remote 3 ALERT
0
Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 3 remote-diode temperature exceeds the programmed temperature
threshold limit in the remote 3 ALERT high-limit register.
1
Remote 2 ALERT
0
Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 2 remote-diode temperature exceeds the temperature threshold limit
in the remote 2 ALERT high-limit register.
0
Remote 1 ALERT
0
Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 1 remote-diode temperature exceeds the temperature threshold limit
in the remote 1 ALERT high-limit register.