NVT210
http://onsemi.com
8
LOW-PASS FILTER
f
C
= 65 kHz
REMOTE
SENSING
TRANSISTOR
BIAS
DIODE
D+
D
V
DD
I
BIAS
I
N1 ?I
V
OUT+
V
OUT
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癈. 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癈. Table 6
lists the data format for the external temperature low byte.
Table 6. EXTENDED TEMPERATURE RESOLUTION
(REMOTE TEMPERATURE LOW BYTE)
Extended Resolution
Remote Temperature
Low Byte
0.00癈
0 000 0000
0.25癈
0 100 0000
0.50癈
1 000 0000
0.75癈
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癈 to +127癈.
However, the NVT210 can be operated using an extended
temperature range. The extended measurement range is
64癈 to +191癈. Therefore, the NVT210 can be used to
measure the full temperature range of an external diode,
from 55癈 to +150癈.
The extended temperature range is selected by setting
Bit 2 of the configuration register to 1. The temperature
range is 0癈 to 127癈 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 NVT210 is limited
by the remote diode selection. The temperature registers can
have values from 64癈 to +191癈. However, most
temperature sensing diodes have a maximum temperature
range of 55癈 to +150癈. Above +150癈, 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 NVT210 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癈 to +120癈.
Temperature Data Format
The NVT210 has two temperature data formats. When the
temperature measurement range is from 0癈 to 127癈
(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癈 in the offset binary
data format. Examples of temperatures in both data formats
are shown in Table 7.