MAX6653 Просмотр технического описания (PDF) - Maxim Integrated

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MAX6653

Temperature Monitors and PWM Fan Controllers

Maxim Integrated 

Temperature Monitors and

PWM Fan Controllers

Register Summary (continued)

Addr(H)

3D

3E

3F

READ/WRITE POR STATE

DESCRIPTION

R

0011 1000 Device ID

R

0100 1101 Manufacturer ID

THERM behavior/revision:

Bit [7]: THERM behavior:

R/W

1000 0000

1: enable THERM as an output.

0: disable THERM as an output.

Bits [3:0] revision number.

*For MAX6663 bit 7 has to be 1 all the time.

PC Board Layout

Follow these guidelines to reduce the measurement

error of the temperature sensors:

1) Place the MAX6653/MAX6663/MAX6664 as close

as is practical to the remote diode. In noisy environ-

ments, such as a computer motherboard, this dis-

tance 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 ISA/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°C error, even with good filtering.

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

close proximity to each other, away from any higher

voltage traces, such as 12VDC. Leakage currents

from PC board contamination must be dealt with

carefully since a 20MΩ leakage path from DXP to

ground causes about 1°C error. If high-voltage

traces are unavoidable, connect guard traces to

GND on either side of the DXP-DXN traces (Figure

6).

4) The 10-mil widths and spacing recommended in

Figure 6 are not absolutely necessary, as they offer

only a minor improvement in leakage and noise over

narrow traces. Use wider traces when practical.

5) Add a 200Ω resistor in series with VCC for best

noise filtering (see Typical Operating Circuits).

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-

10 MILS

10 MILS

GND

10 MILS

DXP

MINIMUM

DXN

10 MILS

GND

Figure 6. Recommended DXP/DXN PC Traces

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

remote sensor. For very long cable runs, the cable’s

parasitic capacitance often provides noise filtering, so

the 2200pF capacitor can often be removed or reduced

in value.

Cable resistance also affects remote-sensor accuracy.

For every 1Ω of series resistance, the error is approxi-

mately 0.5°C.

PC Board Layout Checklist

• Place the MAX6653/MAX6663/MAX6664 close to

the remote-sense junction.

• Keep traces away from high voltages (+12V bus).

• Keep traces away from fast data buses and CRTs.

• Use recommended trace widths and spacings.

• Place a ground plane under the traces.

• Use guard traces flanking DXP and DXN and con-

necting to GND.

• Place the noise filter and the 0.1µF VCC bypass

capacitors close to the MAX6653/MAX6663/

MAX6664.

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