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NE1618

Temperature monitor for microprocessor systems

Philips Electronics 

Philips Semiconductors

Temperature monitor for microprocessor systems

Product data

NE1618

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:

∆VBE = (KT/q)*LN(N)

where:

K: Boltzman’s constant

T: absolute temperature in °K

q: electron charge

LN: natural logarithm

N: ratio of the two operating currents

Because, in measuring the remote diode VBE, the NE1618 provides

two current sources of about 10 µA and 100 µA 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

remote temp with a resolution 0.125 °C. The extended measurement

can be used in enhanced application for monitoring precisely the die

temp of integrated circuits. Because the extended measurement is

corporate with an on-board 11-bit A-to-D converter, the resulted data

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

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

floating number which is made up by two parts: the integer portion is

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)

TEMPERATURE (°C)

8-BIT DIGITAL DATA

+127

0 111 1111

+126

0 111 1110

+100

0 110 0100

+50

0 011 0010

+25

0 001 1001

+1

0 000 0001

≤0

0 000 0000

Table 4. Extended data format (REET)

TEMPERATURE (°C)

8-BIT DIGITAL DATA

0.000

0000 0000

0.125

0010 0000

0.250

0100 0000

0.375

0110 0000

0.500

1000 0000

0.625

1010 0000

0.750

1100 0000

0.875

1110 0000

2002 Jan 04

9

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