MAX6698UE99+【PDF 13/24 页】IC TEMP MONITOR 7CH 16-TSSOP

either the measured value must drop below the thresh-

old minus the hysteresis value (4癈 or 4 LSBs), or the

trip threshold must be set at least 4癈 (or 4 LSBs) above

the current value.

Applications Information

Remote-Diode Selection

The MAX6698 directly measures the die temperature of

CPUs and other ICs that have on-chip temperature-

sensing diodes (see the Typical Application Circuit) or

it can measure the temperature of a discrete diode-

connected transistor.

Effect of Ideality Factor

The accuracy of the remote temperature measurements

depends on the ideality factor (n) of the remote diode

(actually a transistor). The MAX6698 is optimized for n

= 1.008. A thermal diode on the substrate of an IC is

normally a pnp with the base and emitter brought out

the collector (diode connection) grounded. DXP_ must

be connected to the anode (emitter) and DXN_ must be

connected to the cathode (base) of this pnp. If a sense

transistor with an ideality factor other than 1.008 is

used, the output data is different from the data

obtained with the optimum ideality factor. Fortunately,

the difference is predictable. Assume a remote-diode

sensor designed for a nominal ideality factor n

NOMINAL

is used to measure the temperature of a diode with a

different ideality factor n1. The measured temperature

T

M

can be corrected using:

where temperature is measured in Kelvin and

n

NOMIMAL

for the MAX6698 is 1.008. As an example,

assume you want to use the MAX6698 with a CPU that

has an ideality factor of 1.002. If the diode has no

series resistance, the measured data is related to the

real temperature as follows:

For a real temperature of +85癈 (358.15K), the mea-

sured temperature is +82.87癈 (356.02K), an error of

-2.13癈.

Series Resistance Cancellation

Some thermal diodes on high-power ICs can have

excessive series resistance, which can cause tempera-

ture measurement errors with conventional remote tem-

perature sensors. Channel 1 of the MAX6698 has a

series resistance cancellation feature (enabled by bit 3

of the configuration 1 register) that eliminates the effect

of diode series resistance. Set bit 3 to 1 if the series

resistance is large enough to affect the accuracy of

T

n

T

ACTUAL M

NOMINAL

M

=

?/DIV>

=

?/DIV>

=

1

1 008

1 002

1 00599

.

( .

)

T T

n

M

ACTUAL

NOMINAL

=

?/DIV>

1

______________________________________________________________________________________ 13

7-Channel Precision Remote-Diode, Thermistor,

and Local Temperature Monitor

BIT

NAME

POR

STATE

FUNCTION

7(MSB)

Reserved

0

6

Reserved

0

5

Mask Thermistor 3

OVERT

0

Thermistor 3 OVERT Mask Bit. Set to logic 1 to mask thermistor 3 OVERT.

4

Mask Thermistor 2

OVERT

0

Thermistor 2 OVERT Mask Bit. Set to logic 1 to mask thermistor 2 OVERT.

3

Mask Thermistor 1

OVERT

0

Thermistor 1 OVERT Mask Bit. Set to logic 1 to mask thermistor 1 OVERT.

2

Reserved

0

1

Reserved

0

Mask OVERT 1

0

Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1

OVERT.

Table 7. Configuration 3 Register

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