MAX6689UP34+【PDF 14/19 页】IC 7CH PREC TEMP MONITOR 20TSSOP

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Unused Diode Channels

If one or more of the remote diode channels is not

needed, the DXP and DXN inputs for that channel

should either be unconnected, or the DXP input should

be connected to V

. The status register indicates a

diode "fault" for this channel and the channel is ignored

during the temperature-measurement sequence. It is

also good practice to mask any unused channels

immediately upon power-up by setting the appropriate

bits in the Configuration 2 and Configuration 3 regis-

ters. This will prevent unused channels from causing

ALERT or OVERT to assert.

Thermal Mass and Self-Heating

When sensing local temperature, the MAX6689 mea-

sures the temperature of the printed-circuit board

(PCB) to which it is soldered. The leads provide a good

thermal path between the PCB traces and the die. As

with all IC temperature sensors, thermal conductivity

between the die and the ambient air is poor by compar-

ison, making air temperature measurements impracti-

cal. Because the thermal mass of the PCB is far greater

than that of the MAX6689, the device follows tempera-

ture changes on the PCB 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 virtually no effect; the measured temperature of the

junction tracks the actual temperature within a conver-

sion 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 ______________________________________________________________________________________

Table 7. Status 1 Register

BIT

NAME

POR

STATE

FUNCTION

7 (MSB)

Reserved

Local ALERT

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.

Remote 6 ALERT

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.

Remote 5 ALERT

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.

Remote 4 ALERT

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.

Remote 3 ALERT

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.

Remote 2 ALERT

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.

Remote 1 ALERT

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.

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