Datasheet
TCN75A
DS21935A-page 10 © 2005 Microchip Technology Inc.
4.3.1 AMBIENT TEMPERATURE
REGISTER (T
A
)
The TCN75A has a 16-bit read-only Ambient
Temperature register
that contains 9-bit to 12-bit tem-
perature data. This data is formatted in two’s
complement. The bit assignments, as well as the
corresponding resolution, is shown in the register
assignment below.
The refresh rate of this register depends on the
selected ADC resolution. It takes 30 ms (typ.) for 9-bit
data and 240 ms (typ.) for 12-bit data. Since this
register is double-buffered, the user can read the
register while the TCN75A performs analog-to-digital
conversion in the background. The decimal code to
ambient temperature conversion is shown in
Equation 4-2:
EQUATION 4-2:
T
A
Code 2
4–
×=
Where:
T
A
= Ambient Temperature (°C)
Code = TCN75A output in decimal
(Table 4-1)
REGISTER 4-2: AMBIENT TEMPERATURE REGISTER (T
A
)
Upper Half:
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
Sign 2
6
°C/bit 2
5
°C/bit 2
4
°C/bit 2
3
°C/bit 2
2
°C/bit 2
1
°C/bit 2
0
°C/bit
bit 15 bit 8
Lower Half:
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
2
-1
°C/bit 2
-2
°C/bit 2
-3
°C/bit 2
-4
°C/bit 0 0 0 0
bit 7 bit 0
Note: When the 9-bit, 10-bit or 11-bit resolutions are selected, bit 6, bit 7 or bit 8 will remain clear <0>
,
respectively.
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
- n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
TABLE 4-1: CODE CONVERSION
Resolution TCN75A Output (Binary) Hexadecimal Decimal T
A
(°C)
9-Bit
0111 1101 0uuu uuuu
(1)
0FA 250 +125
0001 1001 0uuu uuuu 032 50 +25
0000 0000 1uuu uuuu 001 1 +0.5
10-Bit
0111 1101 00uu uuuu 1F4 500 +125
0001 1001 01uu uuuu 065 101 +25.25
0000 0000 01uu uuuu 001 1 +0.25
11-Bit
0111 1101 000u uuuu 3E8 1000 +125
0001 1001 011u uuuu 0CB 203 +25.375
0000 0000 001u uuuu 001 1 +0.125
12-Bit
0111 1101 0000 uuuu 7D0 2000 +125
0001 1001 0111 uuuu 197 407 +25.4375
0000 0000 0001 uuuu 001 1 +0.0625
0°C
0000 0000 0000 uuuu 000 0 0
12-Bit
1111 1111 1111 uuuu
(2)
001
(3)
-1 -0.0625
1110 0110 1001 uuuu 197 -407 -25.4375
1100 1001 0000 uuuu 370 -880 -55
Note 1: ‘u’ represents unused bits. The TCN75A clears <0> the unused bits.
2: This data is in two’s complement format, which indicates ambient temperature below 0°C.
3: Negative temperature magnitude in hexadecimal. This conversion is accomplished by complimenting each binary bit
and adding 1.