MCP9808
In addition, the TA register uses three bits (TA<15:13>)
to reflect the Alert pin state. This allows the user to
identify the cause of the Alert output trigger (see
Section 5.2.3 “Alert Output Configuration”); bit 15 is
set to ‘1’ if TA is greater than or equal to TCRIT, bit 14 is
set to ‘1’ if TA is greater than TUPPER and bit 13 is set to
5.1.3
AMBIENT TEMPERATURE
REGISTER (TA)
The MCP9808 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 digital word is
loaded to a 16-bit read-only Ambient Temperature
register (TA) that contains 13-bit temperature data in
two’s complement format.
‘1’ if TA is less than TLOWER
.
The TA register bit assignment and boundary
conditions are described in Register 5-4.
The TA register bits (TA<12:0>) are double-buffered.
Therefore, the user can access the register, while in the
background, the MCP9808 performs an Analog-to-
Digital conversion. The temperature data from the ΔΣ
ADC is loaded in parallel to the TA register at tCONV
refresh rate.
REGISTER 5-4:
TA: AMBIENT TEMPERATURE REGISTER (→ ADDRESS ‘0000 0101’b)(1)
R-0
R-0
R-0
R-0
R-0
R-0
R-0
R-0
(1)
(1)
(1)
TA vs. TCRIT
bit 15
TA vs. TUPPER
TA vs. TLOWER
SIGN
27 °C
26 °C
25 °C
24 °C
bit 8
R-0
23 °C
R-0
22 °C
R-0
21 °C
R-0
20 °C
R-0
2-1 °C
R-0
2-2 °C(2)
R-0
2-3 °C(2)
R-0
2-4 °C(2)
bit 7
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
bit 15
bit 14
bit 13
bit 12
bit 11-0
TA vs. TCRIT bit(1)
0 = TA < TCRIT
1 = TA ≥ TCRIT
TA vs. TUPPER bit(1)
0= TA ≤ TUPPER
1= TA > TUPPER
TA vs. TLOWER bit(1)
0= TA ≥ TLOWER
1= TA < TLOWER
SIGN bit
0= TA ≥ 0°C
1= TA < 0°C
TA: Ambient Temperature bits(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 Alert Output Configuration (CONFIG<5:0> bits,
Register 5-2).
2: Bits 2, 1 and 0 may remain clear at ‘0’ depending on the status of the Resolution register (Register 5-7).
The power-up default is 0.25°C/bit; bits 1 and 0 remain clear ‘0’.
DS25095A-page 24
© 2011 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
