Microchip Technology TMPSNSRD-TCPL1 Hoja De Datos
MCP9804
DS22203C-page 24
© 2009-2012 Microchip Technology Inc.
5.1.3
AMBIENT TEMPERATURE
REGISTER (T
REGISTER (T
A
)
The MCP9804 uses a band gap temperature sensor
circuit to output analog voltage proportional to absolute
temperature. An internal
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 digital word is
loaded to a 16-bit read-only Ambient Temperature
register
loaded to a 16-bit read-only Ambient Temperature
register
(T
A
)
that contains 13-bit temperature data in
two’s complement format.
The T
A
register bits (T
A
<12:0>) are double-buffered.
Therefore, the user can access the register, while in the
background, the MCP9804 performs an Analog-to-
Digital conversion. The temperature data from the
background, the MCP9804 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 (T
A
<15:13>)
to reflect the Alert pin state. This allows the user to
identify the cause of the Alert output trigger (see
identify the cause of the Alert output trigger (see
); 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 5-4:
T
A
: AMBIENT TEMPERATURE REGISTER (
→ ADDRESS ‘0000 0101’b)
(
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
bit
(
)
0
= T
A
< T
CRIT
1
= T
A
≥ T
CRIT
bit 14
T
A
vs. T
UPPER
bit
0
= T
A
≤ T
UPPER
1
= T
A
> T
UPPER
bit 13
T
A
vs. T
LOWER
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
T
A
: Ambient Temperature bits
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 Alert Output Configuration (CONFIG<5:0> bits,
2:
Bits 2, 1 and 0 may remain clear at ‘0’ depending on the status of the Resolution register (
The power-up default is 0.25°C/bit; bits 1 and 0 remain clear ‘0’.