Datasheet
MCP9843/98243
DS22153C-page 26 © 2009 Microchip Technology Inc.
5.1.4 AMBIENT TEMPERATURE
REGISTER (T
A
)
The MCP9843/98243 device uses a band gap
temperature sensor circuit to output analog voltage
proportional to absolute temperature. An internal ΔΣ
ADC is used to convert the analog voltage to a digital
word. The converter resolution is set to 0.25°C + sign
(11-bit data). The digital word is loaded to a 16-bit read-
only Ambient Temperature register
(T
A
) that contains
11-bit temperature data in two’s complement format.
The T
A
register bits (bits 12 thru 0) are double-buffered.
Therefore, the user can access the register while, in the
background, the MCP9843/98243 performs an analog-
to-digital conversion. The temperature data from the ΔΣ
ADC is loaded in parallel to the T
A
register at t
CONV
refresh rate.
In addition, the T
A
register uses three bits (bits 15, 14
and 13) to reflect the Event pin state. This allows the
user to identify the cause of the Event output trigger
(see Section 5.2.3 “Event Output Configuration”);
bit 15 is set to ‘1’ if T
A
is greater than or equal to T
CRIT
,
bit 14 is set to ‘1’ if T
A
is greater than T
UPPER
and bit 13
is set to ‘1’ if T
A
is less than T
LOWER
.
The T
A
register bit assignment and boundary
conditions are described in Register 5-5.
REGISTER 5-5: AMBIENT TEMPERATURE REGISTER (T
A
) → ADDRESS ‘0000 0101’b (NOTE 1)
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
T
A
vs. T
CRIT
T
A
vs. T
UPPER
T
A
vs. T
LOWER
SIGN 2
7
°C 2
6
°C 2
5
°C 2
4
°C
bit 15 bit 8
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
2
3
°C 2
2
°C 2
1
°C 2
0
°C 2
-1
°C 2
-2
°C 2
-3
°C 2
-4
°C
bit 7 bit 0
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
bit 15 T
A
vs. T
CRIT
(1)
Bit:
0
=T
A
< T
CRIT
1 =T
A
≥ T
CRIT
bit 14 T
A
vs. T
UPPER
(1)
Bit:
0 =T
A
≤ T
UPPER
1 =T
A
> T
UPPER
bit 13 T
A
vs. T
LOWER
(1)
Bit:
0 =T
A
≥ T
LOWER
1 =T
A
< T
LOWER
bit 12 SIGN Bit:
0 =T
A
≥ 0°C
1 =T
A
< 0°C
bit 11-0 Ambient Temperature (T
A
) Bits: (Note 2)
12-bit Ambient Temperature data in two’s complement format.
Note 1: Bits 15, 14 and 13 are not affected by the status of the Event output configuration (bits 5 to 0 of CONFIG)
(Register 5-3).
2: Bits 2, 1, and 0 may remain clear '0' depending on the status of the resolution register (Register 5-9).
The Power-up default is 0.25°C/bit, bits 1 and 0 remain clear '0'.