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NE1617A-2009 View Datasheet(PDF) - NXP Semiconductors.

Part NameDescriptionManufacturer
NE1617A(2009) Temperature monitor for microprocessor systems NXP
NXP Semiconductors. NXP
NE1617A Datasheet PDF : 27 Pages
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NXP Semiconductors
Temperature monitor for microprocessor systems
7. Functional description
The NE1617A contains an integrating A-to-D converter, an analog multiplexer, a status
register, digital data registers, SMBus interface, associated control logic and a local
temperature sensor or channel (refer to Figure 1 “Block diagram of NE1617A”). The
remote diode-type sensor or channel should be connected to the D+ and Dpins properly.
Temperature measurements or conversions are either automatically and periodically
activated when the device is in free-running mode (both STBY pin = HIGH, and the
configuration register bit 6 = LOW) or generated by one-shot command. The free-running
period is selected by changing the programmable data of the conversion rate register, as
described in Section 8.3.4. For each conversion, the multiplexer switches current sources
through the remote and local temperature sensors over a period of time, about 60 ms, and
the voltages across the diode-type sensors are sensed and converted into the
temperature data by the A-to-D converter. The resulting temperature data is then stored in
the temperature registers, in 8-bit two's complement word format and automatically
compared with the limits which have been programmed in the temperature limit registers.
Results of the comparison are reflected accordingly by the flags stored in the status
register, an out-of-limit condition will set the ALERT output pin to its LOW state. Because
both channels are automatically measured for each conversion, the results are updated
for both channels at the end of every successful conversion.
7.1 Remote diode selection
The method of the temperature measurement is based on the change of the diode VBE at
two different operating current levels given by:
V BE = K---q--T-- × LN (N )
VBE = change in base emitter voltage drop at two current levels
K = Boltzman’s constant
T = absolute temperature in ° Kelvin
q = charge on the electron
LN = natural logarithm
N = ratio of the two currents
The NE1617A forces two well-controlled current sources of about 10 µA and 100 µA and
measures the remote diode VBE. The sensed voltage between two pins D+ and Dis
limited between 0.25 V and 0.95 V. The external diode must be selected to meet this
voltage range at these two current levels. The diode-connected PNP transistor provided
on the microprocessor is typically used, or the discrete diode-connected transistor
2N3904 or 2N3906 is recommended as an alternative.
Even though the NE1617A integrating A-to-D converter has a good noise performance,
using the average of 10 measurement cycles, high frequency noise filtering between D+
and Dshould be considered. An external capacitor of 2200 pF typical (but not higher
Product data sheet
Rev. 04 — 30 July 2009
© NXP B.V. 2009. All rights reserved.
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