Five-Channel Precision Temperature Monitor

14

______________________________________________________________________________________

BIT

NAME

POR

STATE

FUNCTION

7 (MSB)

Reserved

0

—

6

Reserved

0

Not Used. 0 at POR, then 1.

5

Reserved

0

Not Used. 0 at POR, then 1.

4Diode fault 4

0

Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4

are either shorted or open circuit.

3Diode fault 3

0

Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3

are either shorted or open circuit.

2Diode fault 2

0

Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2

are either shorted or open circuit.

1Diode fault 1

0

Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1

are either shorted or open circuit.

0

Reserved

0

—

Table 9. Status 3 Register

Applications Information

Remote-Diode Selection

The MAX6602 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 measure-

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

“diode” (actually a transistor). The MAX6602 is opti-

mized for n = 1.012. 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 1.012 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

a diode with a different ideality factor n1. The measured

where temperature is measured in Kelvin and

assume you want to use the MAX6602 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°C (358.15K), the mea-

sured temperature is +81.46°C (354.61K), an error of

-3.539°C.

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 MAX6602 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

channel 1. The series resistance cancellation function

increases the conversion time for channel 1 by 125ms.

This feature cancels the bulk resistance of the sensor

and any other resistance in series (wire, contact resis-

tance, etc.). The cancellation range is from 0 to 100

Ω.

TT

n

n

TT

ACTUAL

M

NOMINAL

MM

=×









=× 







=

1

1 012

1 002

1 00998

.

.

(.

)

TT

n

n

M

ACTUAL

NOMINAL

=









1