MAX6699EE34+【PDF 16/19 页】IC TEMP MONITOR 5CH 16-QSOP

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ADC Noise Filtering

The integrating ADC has good noise rejection for low-

frequency signals, such as power-supply hum. In envi-

ronments with significant high-frequency EMI, connect

an external 2200pF capacitor between DXP_ and

DXN_. Larger capacitor values can be used for added

filtering, but do not exceed 3300pF because it can

introduce errors due to the rise time of the switched

current source. High-frequency noise reduction is

needed for high-accuracy remote measurements.

Noise can be reduced with careful PCB layout as dis-

cussed in the PCB Layout section.

Slave Address

Table 11 shows the MAX6699 slave address.

PCB Layout

Follow these guidelines to reduce the measurement

error when measuring remote temperature:

1) Place the MAX6699 as close as is practical to the

remote diode. In noisy environments, such as a

computer motherboard, this distance can be 4in to

8in (typ). This length can be increased if the worst

noise sources are avoided. Noise sources include

CRTs, clock generators, memory buses, and PCI

buses.

2) Do not route the DXP-DXN lines next to the deflec-

tion coils of a CRT. Also, do not route the traces

across fast digital signals, which can easily intro-

duce +30癈 error, even with good filtering.

3) Route the DXP and DXN traces in parallel and in

close proximity to each other. Each parallel pair of

traces should go to a remote diode. Route these

traces away from any higher voltage traces, such as

+12VDC. Leakage currents from PCB contamination

must be dealt with carefully since a 20M& leakage

path from DXP to ground causes about +1癈 error.

If high-voltage traces are unavoidable, connect

guard traces to GND on either side of the DXP-DXN

traces (Figure 5).

4) Route through as few vias and crossunders as pos-

sible to minimize copper/solder thermocouple

effects.

5) Use wide traces when practical.

6) When the power supply is noisy, add a resistor (up

to 47&) in series with V

Twisted-Pair and Shielded Cables

Use a twisted-pair cable to connect the remote sensor

for remote-sensor distances longer than 8in or in very

noisy environments. Twisted-pair cable lengths can be

between 6ft and 12ft before noise introduces excessive

errors. For longer distances, the best solution is a

shielded twisted pair like that used for audio micro-

phones. For example, Belden #8451 works well for dis-

tances up to 100ft in a noisy environment. At the

device, connect the twisted pair to DXP and DXN and

the shield to GND. Leave the shield unconnected at the

5-Channel Precision Temperature Monitor

16 ______________________________________________________________________________________

5 mils

MINIMUM

5 mils

GND

DXP

DXN

GND

Figure 5. Recommended Minimum DXP-DXN PCB Traces

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

Note: Discrete transistors must be diode connected (base

shorted to collector).

PART

SMBus SLAVE ID

PIN-PACKAGE

MAX

EE 4

0011 010

16 QSOP

MAX

0011 100

16 QSOP

MAX

1001 100

16 QSOP

MAX

1001 110

16 QSOP

MAX

E 4

0011 010

16 TSSOP

MAX

0011 100

16 TSSOP

MAX

1001 100

16 TSSOP

MAX

1001 110

16 TSSOP

Table 11. Slave Address

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