ne1618 NXP Semiconductors, ne1618 Datasheet - Page 9

• Manufacturer Part Number: ne1618
• Description: Temperature Monitor For Microprocessor Systems
• Manufacturer: NXP Semiconductors

remote temp with a resolution 0.125 C. The extended measurement
corporate with an on-board 11-bit A-to-D converter, the resulted data
Philips Semiconductors
free-running mode. In hardware standby mode, the A-to-D converter
is disabled and conversion operation is inhibited.
Notice that if a hardware standby command is received when the
device is in free-running mode with a conversion is in progress, the
conversion cycle will stop and the register data will not be updated.
Temperature measurement
The NE1618 contains an on-chip temp sensor for measuring the
local or internal temperature and provides input pins D+ and D– for
connecting to a remote temp sensor in order to measure the remote
or external temperature. The remote sensor should be a diode-type
sensor and must be connected to the D+ and D– pins properly:
anode to the D+ and cathode to the D–.
The method of temp measurement is based on the difference of the
diode VBE at two operating current levels given by:
where:
Because, in measuring the remote diode VBE, the NE1618 provides
two current sources of about 10 A and 100 A and the sensed
voltage between two pins D+ and D– is limited within 0.25 V and
0.95 V, the external diode should be selected to meet these current
and voltage requirements. The diode-connected PNP transistor
provided on the Pentium series microprocessor is typically used, or
the discrete diode-connected low-power transistor 2N3904 is
recommended.
When the temperature is measured, local and remote, the VBE is
converted into digital data by the on-chip sigma-delta A-to-D
converter. The results are stored in the three temp registers (RIT,
RET and REET) and also compared with the limits stored in the
temp limits registers in order to set accordingly the flag bits in the
status register and to generate interruption if any fault condition
occurs. The content of temp registers are updated upon completion
of every conversion and they can be read at any time.
In the addition of providing the basic measurement with a resolution
of 1 C, the NE1618 includes the extended measurement for the
can be used in enhanced application for monitoring precisely the die
temp of integrated circuits. Because the extended measurement is
is an 11-bit digital number which is divided into two groups for
storing into two registers RET and REET. The group of eight MSB
bits of the data is stored in the RET register and the group of three
LSB bits of the data is stored in the REET register in its MSB
positions. Therefore, the data of those two registers must be
correctly combined to get the extended remote temp data.
When the device is in basic measuring mode (by setting the
conversion rate data higher than 04h) the A-to-D converter uses
2002 Jan 04
VBE = (KT/q)*LN(N)
Temperature monitor for microprocessor systems
K: Boltzman’s constant
T: absolute temperature in K
q: electron charge
LN: natural logarithm
N: ratio of the two operating currents
9
floating number which is made up by two parts: the integer portion is
only 8 bits for the conversion, the REET content is cleared. Only the
8-bit data stored in the RET with resolution of 1 C is significant for
the remote temperature.
Notice that the extended measurement only works if the device is in
its free-running operation mode. It does not work when the device is
in its standby mode and the conversion is activated by a one-shot
command. A one-shot command will produce the same result as of
basic measurement instead of the extended measurement even
though the slow conversion rate has been selected.
Temperature data format
For local temp measurement, because the extended mode has no
effect to the measurement, the resulted temp value can be integer
number which is equivalent to the 2’s complement value of the 8-bit
byte data of the RIT register with 1 C resolution as shown in
Table 3.
For remote temp measurement, the resulted temp value can be a
derived from the RET data using data format as shown in Table 3
and the decimal or extended portion is derived from the REET data
using data format as shown in Table 4. Notice that when the device
is in basic measurement mode (by setting the conversion data more
than 04h) the extended portion is always equal to 0 and the resulted
data is only the one which is derived from RET register with 1 C
resolution.
Table 3. Temperature data format (RIT & RET)
Table 4. Extended data format (REET)
TEMPERATURE ( C)
+127
+126
+100
+50
+25
+1
TEMPERATURE ( C)
0.000
0.125
0.250
0.375
0.500
0.625
0.750
0.875
0
8-BIT DIGITAL DATA
0 111 1111
0 111 1110
0 110 0100
0 011 0010
0 001 1001
0 000 0001
0 000 0000
8-BIT DIGITAL DATA
0000 0000
0010 0000
0100 0000
0110 0000
1000 0000
1010 0000
1100 0000
1110 0000
NE1618
Product data