NE1617DS NXP Semiconductors, NE1617DS Datasheet - Page 9

• Manufacturer Part Number: NE1617DS
• Description: Board Mount Temperature Sensors I2C LOC +/- 2OC AND REM +/- 3OC TS
• Manufacturer: NXP Semiconductors

Specifications of NE1617DS

• Full Temp Accuracy: +/- 3 C, +/- 5 C
• Package / Case: SSOP-16
• Digital Output - Bus Interface: 2-Wire
• Maximum Operating Temperature: + 120 C
• Minimum Operating Temperature: 0 C
• Output Type: Digital
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: NE1617DS,112

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The NE1617 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. The remote diode-type sensor or channel should be
connected to the D+ and D– pins 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 BIT6 = 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 later. For each conversion, the multiplexer switches
current sources through the remote and local temperature sensors
over a period of time, about 60ms, 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.
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:
where:
2004 Oct 06
Temperature monitor for microprocessor systems
K: Boltzman’s constant
T: absolute temperature in Kelvin
q: charge on the electron
N: ratio of the two currents
LN: natural logarithm
VBE
KT
q
LN(N)
9
The NE1617 provides two current sources of about 10 A and 100 A
in measuring the remote diode VBE. The diode-connected PNP
transistor provided on the microprocessor is typically used, or the
discrete diode-connected transistor 2N3904 is recommended as an
alternative.
Even though the NE1617 integrating A-to-D converter has a good
noise performance, using the average of 10 measurement cycles,
high frequency noise filtering between D+ and D– should be
considered. An external capacitor of 2200pF typical (but not higher
than 3300 pF) connected between D+ and D– is recommended.
Capacitance higher than 3300 pF will introduce measurement error
due to the rise time of the switched current source.
Address logic
The address pins of the NE1617 can be forced into one of three
levels: Low (GND), High (V
NE1617 samples and latches the address pins at the starting of
every conversion, it is suggested that those address pins should be
hardwired to the logic applied, so that the logic is consistently
existed at the address pins. During the address sensing period, the
device forces a current at each address pin and compares the
voltage developed across the external connection with the
predefined threshold voltage in order to define the logic level. If an
external resistor is used for the connection of the address, then its
value should be less than 2 k to prevent the error in logic detection
from happening. Resistors of 1 k is recommended.
DD
), or not connected (NC). Because the
Product specification
NE1617