5.4 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.

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.

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 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 ‘1’ if TA is less than TLOWER.

The TA register bit assignment and boundary conditions are described in Table 5-5.

Table 5-5. TA: Ambient Temperature Register (→ Address ‘0000 0101’B)(1)
R-0R-0R-0R-0R-0R-0R-0R-0
TA vs. TCRIT(1)TA vs. TUPPER(1)TA vs. TLOWER(1)SIGN27 °C26 °C25 °C24 °C
bit 15bit 8
R-0R-0R-0R-0R-0R-0R-0R-0
23 °C22 °C21 °C20 °C2-1 °C2-2 °C(2)2-3 °C(2)2-4 °C(2)
bit 7bit 0
R = Readable bitW = Writable bitU = Unimplemented bit, read as ‘0’
-n = Value at POR‘1’ = Bit is set‘0’ = Bit is clearedx = Bit is unknown
15TA vs. TCRIT bit(1)

0 = TA < TCRIT

1 = TA ≥ TCRIT

14TA vs. TUPPER bit(1)

0 = TA ≤ TUPPER

1 = TA > TUPPER

13TA vs. TLOWER bit(1)

0 = TA ≥ TLOWER

1 = TA < TLOWER

12SIGN bit

0 = TA ≥ 0°C

1 = TA < 0°C

11-0TA: 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, Table 5-3).
  2. Bits 2, 1 and 0 may remain clear at ‘0’ depending on the status of the Resolution register (Table 5-8). The power-up default is 0.25°C/bit; bits 1 and 0 remain clear ‘0’.