NVT211

http://onsemi.com

8

LOW-PASS FILTER

REMOTE

SENSING

TRANSISTOR

BIAS

DIODE

D+

D−

I

N1 × I

To ADC

N2 × I

C1*

*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1,000 pF 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 5

lists the data format for the external temperature low byte.

Table 5. EXTENDED TEMPERATURE RESOLUTION

(REMOTE TEMPERATURE LOW BYTE)

Extended Resolution

Remote Temperature

Low Byte

0.00°C

0 000 0000

0.25°C

0 100 0000

0.50°C

1 000 0000

0.75°C

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 NVT211 can be operated using an extended

temperature range. The extended measurement range is

−64

°C to +191°C. Therefore, the NVT211 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 NVT211 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 NVT211 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 NVT211 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 6.