MAX6656MEE Maxim Integrated Products, MAX6656MEE Datasheet - Page 10

• Manufacturer Part Number: MAX6656MEE
• Description: Board Mount Temperature Sensors Dual Remote/Local Temperature Sensor
• Manufacturer: Maxim Integrated Products

Specifications of MAX6656MEE

• Full Temp Accuracy: +/- 3 C
• Package / Case: QSOP-16
• Digital Output - Bus Interface: Serial (2-Wire)
• Digital Output - Number Of Bits: 11 bit
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• Output Type: Digital

places constraints on high-frequency noise rejection.
Lay out the PC board carefully with proper external
noise filtering for high-accuracy remote measurements
in electrically noisy environments. Filter high-frequency
electromagnetic interference (EMI) at DXP and DXN
with an external 2200pF capacitor connected between
the two inputs. This capacitor can be increased to
about 3300pF (max), including cable capacitance. A
capacitance higher than 3300pF introduces errors due
to the rise time of the switched-current source.
If necessary, bypass V
value capacitor for greater noise performance. Do not
put resistance in series with the inputs. Series resis-
tance degrades voltage measurements.
1) Place the MAX6655/MAX6656 as close as practical
2) Do not route the DXP-DXN lines next to the deflec-
3) Route the DXP and DXN traces parallel and close to
4) Connect guard traces to GND on either side of the
5) Route as few vias and crossunders as possible to
6) When introducing a thermocouple, make sure that
7) Use wide traces. Narrow traces are more inductive
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
10
to the remote diode. In a noisy environment, such as
a computer motherboard, this distance can be 4in to
8in (typ) or more, as long as the worst noise sources
(such as CRTs, clock generators, memory buses,
and ISA/PCI buses) are avoided.
tion coils of a CRT. Also, do not route the traces
across a fast memory bus, which can easily intro-
duce +30°C error, even with good filtering.
Otherwise, most noise sources are fairly benign.
each other, away from any high-voltage traces such
as +12VDC. Avoid leakage currents from PC board
contamination. A 20mΩ leakage path from DXP to
ground causes approximately +1°C error.
DXP-DXN traces when possible (Figure 5). With
guard traces in place, routing near high-voltage
traces is no longer an issue.
minimize copper/solder thermocouple effects.
both the DXP and the DXN paths have matching
thermocouples. In general, PC board-induced ther-
mocouples are not a serious problem. A copper-sol-
der thermocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP-DXN to
cause a 1°C measurement error, so most parasitic
thermocouple errors are swamped out.
and tend to pick up radiated noise. The 10-mil
widths and spacings recommended in Figure 5 are
not absolutely necessary (as they offer only a minor
______________________________________________________________________________________
IN
_ pins with any appropriate-
PC Board Layout
8) Note that copper cannot be used as an EMI shield.
For remote-sensor distances longer than 8in, or in par-
ticularly noisy environments, a twisted pair is recom-
mended. Its practical length is 6ft to 12ft (typ) before
noise becomes a problem, as tested in a noisy elec-
tronics laboratory. For longer distances, the best solu-
tion is a shielded twisted pair like that used for audio
microphones. For example, Belden #8451 works well
for distances up to 100ft in a noisy environment.
Connect the twisted pair to DXP and DXN and the
shield to GND, and leave the shield’s remote end unter-
minated. Excess capacitance at DX_ limits practical
remote-sensor distances (see Typical Operating
Characteristics).
For very long cable runs, the cable's parasitic capaci-
tance often provides noise filtering, so the recommend-
ed 2200pF capacitor can often be removed or reduced
in value.
Cable resistance also affects remote-sensor accuracy.
A 1Ω series resistance introduces about +1/2°C error.
TRANSISTOR COUNT: 26,783
PROCESS: BiCMOS
Figure 5. Recommended DXP/DXN PC Traces
10MILS
10MILS
improvement in leakage and noise), but use them
where practical.
Placing a copper ground plane between the DXP-
DXN traces and traces carrying high-frequency
noise signals does not help reduce EMI.
Twisted Pair and Shielded Cables
GND
DXP
DXN
GND
Chip Information
10MILS
MINIMUM
10MILS