MCP9808 datasheet(24/52 Pages) MICROCHIP

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MCP9808

DS25095A-page 24

5.1.3

AMBIENT TEMPERATURE

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

(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

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

‘1’ if TA is less than TLOWER.

The

TA register bit assignment and boundary

conditions are described in Register 5-4.

TA: AMBIENT TEMPERATURE REGISTER (→ ADDRESS ‘0000 0101’b)(1)

R-0

TA vs. TCRIT

(1) T

A vs. TUPPER

(1) T

A vs. TLOWER

(1)

SIGN

27 °C

26 °C

25 °C

24 °C

bit 15

bit 8

R-0

23 °C

22 °C

21 °C

20 °C

2-1 °C

2-2 °C(2)

2-3 °C(2)

2-4 °C(2)

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

TA vs. TCRIT bit(1)

=TA < TCRIT

=TA ≥ TCRIT

bit 14

TA vs. TUPPER bit(1)

=TA ≤ TUPPER

=TA > TUPPER

bit 13

TA vs. TLOWER bit(1)

=TA ≥ TLOWER

=TA < TLOWER

bit 12

SIGN bit

=TA ≥ 0°C

=TA < 0°C

bit 11-0

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,

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’.

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