MAX6694TE9A+T【PDF 15/18 页】IC TEMP MONITOR 5CH 16TQFN

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5-Channel Precision Temperature Monitor

with Beta Compensation

______________________________________________________________________________________ 15

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

sured temperature is +84.41癈 (357.56K), an error of

-0.590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 MAX6694 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&.

Beta Compensation

The MAX6694 is optimized for use with a substrate pnp

remote-sensing transistor on the die of the target IC.

DXP1 connects to the emitter of the sensing transistor

and DXN1 connects to the base. The collector is

grounded. Such transistors can have very low beta

(less than 1) when built in processes with 65nm and

smaller geometries. Because of the very low beta, stan-

dard remote diode temperature sensors may exhibit

large errors when used with these transistors. Channel

1 of the MAX6694 incorporates a beta compensation

function that, when enabled, eliminates the effect of low

beta values. This function is enabled at power-up and

can be disabled using bit 2 of the configuration 1 regis-

ter. Whenever low beta compensation is enabled,

series-resistance cancellation must be enabled. When

a sense transistors base and collector are shorted

together (as with a discrete sensing diode), disable

beta compensation.

Discrete Remote Diodes

When the remote-sensing diode is a discrete transistor,

its collector and base must be connected together.

Table 10 lists examples of discrete transistors that are

appropriate for use with the MAX6694. The transistor

must be a small-signal type with a relatively high for-

ward voltage; otherwise, the A/D input voltage range

BIT

NAME

POR

STATE

FUNCTION

7 (MSB)

Reserved

Not Used. 0 at POR, then 1.

Reserved

Not Used. 0 at POR, then 1.

Diode fault 4

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

are open circuit or when DXP4 is connected to V

Diode fault 3

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

are open circuit or when DXP3 is connected to V

Diode fault 2

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

are open circuit or when DXP2 is connected to V

Diode fault 1

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

are open circuit or when DXP1 is connected to V

Reserved

Table 9. Status 3 Register

MANUFACTURER

MODEL NO.

Central Semiconductor (USA)

CMPT3904

Rohm Semiconductor (USA)

SST3904

Samsung (Korea)

KST3904-TF

Siemens (Germany)

SMBT3904

Zetex (England)

FMMT3904CT-ND

Table 10. Remote-Sensors Transistor

Manufacturers (for Channels 2, 3, and 4)

Note: Discrete transistors must be diode connected (base

shorted to collector).

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