NCT1008CMT3R2G 查看數據表（PDF） - ON Semiconductor

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NCT1008CMT3R2G

±1°C Temperature Monitor with Series Resistance Cancellation

ON Semiconductor 

NCT1008

VDD

I

N1 y I N2 y I

IBIAS

REMOTE

SENSING

TRANSISTOR

D+

C11

D–

BIAS

DIODE

fC = 65kHz

VOUT+

TO ADC

VOUT–

1CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.

C1 = 1000pF MAX.

Figure 14. Input Signal Conditioning

Temperature Measurement Results

The results of the local and remote temperature

measurements are stored in the local and remote temperature

value registers and compared with limits programmed into

the local and remote high and low limit registers.

The local temperature value is in Register 0x00 and has a

resolution of 1°C. The external temperature value is stored

in two registers, with the upper byte in Register 0x01 and the

lower byte in Register 0x10. Only the two MSBs in the

external temperature low byte are used giving the external

temperature measurement a resolution of 0.25°C. Table 1

lists the data format for the external temperature low byte.

Table 1. Extended Temperature Resolution

(Remote Temperature Low Byte

Extended Resolution Remote Temperature Low Byte

0.00°C

0.25°C

0.50°C

0.75°C

0 000 0000

0 100 0000

1 000 0000

1 100 0000

When reading the full external temperature value, read the

LSB first. This causes the MSB to be locked (that is, the

ADC does not write to it) until it is read. This feature ensures

that the results read back from the two registers come from

the same measurement.

Temperature Measurement Range

The temperature measurement range for both internal and

external measurements is, by default, 0°C to +127°C.

However, the NCT1008 can be operated using an extended

temperature range. The extended measurement range is

−64°C to +191°C. Therefore, the NCT1008 can be used to

measure the full temperature range of an external diode,

from −55°C to +150°C.

The extended temperature range is selected by setting Bit

2 of the configuration register to 1. The temperature range

is 0°C to 127°C when Bit 2 equals 0. A valid result is

available in the next measurement cycle after changing the

temperature range.

In extended temperature mode, the upper and lower

temperature that can be measured by the NCT1008 is limited

by the remote diode selection. The temperature registers can

have values from −64°C to +191°C. However, most

temperature sensing diodes have a maximum temperature

range of −55°C to +150°C. Above +150°C, they may lose

their semiconductor characteristics and approximate

conductors instead. This results in a diode short. In this case,

a read of the temperature result register gives the last good

temperature measurement. Therefore, the temperature

measurement on the external channel may not be accurate

for temperatures that are outside the operating range of the

remote sensor.

It should be noted that although both local and remote

temperature measurements can be made while the part is in

extended temperature mode, the NCT1008 itself should not

be exposed to temperatures greater than those specified in

the absolute maximum ratings section. Further, the device is

only guaranteed to operate as specified at ambient

temperatures from −40°C to +120°C.

Temperature Data Format

The NCT1008 has two temperature data formats. When the

temperature measurement range is from 0°C to 127°C

(default), the temperature data format for both internal and

external temperature results is binary. When the measurement

range is in extended mode, an offset binary data format is used

for both internal and external results. Temperature values are

offset by 64°C in the offset binary data format. Examples of

temperatures in both data formats are shown in Table 2.

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