MAX6693
7-Channel Precision Temperature Monitor
with Beta Compensation
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effect; the measured temperature of the junction tracks
the actual temperature within a conversion cycle.
When measuring temperature with discrete remote tran-
sistors, the best thermal response times are obtained
with transistors in small packages (i.e., SOT23 or SC70).
Take care to account for thermal gradients between the
heat source and the sensor, and ensure that stray air
currents across the sensor package do not interfere with
measurement accuracy. Self-heating does not signifi-
cantly affect measurement accuracy. Remote-sensor
self-heating due to the diode current source is negligible.
ADC Noise Filtering
The integrating ADC has good noise rejection for low-
frequency signals, such as power-supply hum. In environ-
ments with significant high-frequency EMI, connect an
external 100pF capacitor between DXP_ and DXN_.
Larger capacitor values can be used for added filtering,
but do not exceed 100pF 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 discussed in the
PCB Layout
section.
Slave Address
The slave address for the MAX6693 is shown in Table 11.
PCB Layout
Follow these guidelines to reduce the measurement
error when measuring remote temperature:
1) Place the MAX6693 as close as is practical to the
remote diode. In noisy environments, such as a com-
puter 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°C 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 20MΩ leakage path from
DXP to ground causes about +1°C error. If high-volt-
age 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 possi-
ble to minimize copper/solder thermocouple effects.
5) Use wide traces when practical. 5mil to 10mil traces
are typical. Be aware of the effect of trace resistance on
temperature readings when using long, narrow traces.
6) When the power supply is noisy, add a resistor (up
to 47Ω) in series with V
CC
.
