AMC6821 datasheet(13/54 Pages) TI

13 / 54 page

www.ti.com

ADCand

Signal

Processing

Remote

Temperature

Registers

LPFand

SignalConditioning

SW1

SW2

BiasDiode

BIAS

IN+

IN-

Substrate

Sensing

Transistor

Series Resistance Cancellation

Reading Temperature Data

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

The remote sensing transistor can be a substrate transistor built within the microprocessor (as in a Pentium-IV),

or a discrete small-signal type transistor. This architecture is shown in Figure 13. The internal bias diode biases

the IN– terminal above ground to prevent the ground noise from interfering with the measurement. An external

capacitor (up to 1000pF) may be placed between IN+ and IN– to further reduce the noise from interfering.

Figure 13. Remote Temperature Sensor

The analog sensing signal is pre-processed by a low-pass filter and signal conditioning circuitry, then digitized by

the ADC. The resulting digital signal is further processed by the digital filter and processing unit. The final result

is stored in the local temperature data register and remote temperature data register, respectively. The eight

MSBs are stored in the corresponding Temp-DATA-HByte register, and the three LSBs are stored in the

Temp-DATA-LByte register. Refer to the Temperature Data Registers section for details.

The format of the final result is in two’s complement; see Table 11. It should be noted that the device measures

the temperature from –40

°C to +125°C, although the code represents temperature from –128°C to +127°C.

Parasitic resistance (seen in series with the remote diode) to the IN+ and IN– inputs to the AMC6821 is caused

by a variety of factors, including printed circuit board (PCB) trace resistance and trace length. This series

resistance appears as a temperature offset in the remote sensor temperature measurement, and causes more

than 0.45

°C error per ohm. The AMC6821 is implemented with a TI-patented technology to automatically cancel

out the effect of this series resistance, giving a more accurate result without the need for user characterization of

this resistance. With this technology, the AMC6821 is able to reduce the effects of series resistance to typically

less than 0.0025

°C per ohm.

It is important to note that temperature can be read by an 8-bit value (with 1

°C of resolution) from the

Temp-DATA-HByte register, or as an 11-bit value (with 0.125

°C of resolution) from the Temp-DATA-LByte and

Temp-DATA-HByte registers. If only 1

°C of resolution is required, the temperature readings can be read back at

any time and in no particular order. If reading the 11-bit measurement is required, the process involves a

two-register read for each measurement. To get an 11-bit result of the remote sensor, the controller must read

the Temp-DATA-LByte register (0x06) first, and then the Remote-Temp-DATA-HByte register (0x0B) to complete

the reading. However, to get bit 11 of the local sensor only, or to get both local and remote sensors, the

controller

must

read

Temp-DATA-LByte

first,

Local-Temp-DATA-HByte

(0x0A)

second,

and

Remote-Temp-DATA-HByte third. This method causes all associated temperature data registers to be frozen

until the Remote-Temp-DATA-HByte register has been read. This process also prevents the high byte data from

being updated while the three LSBs are being read, and vice-versa.

Submit Documentation Feedback

Product Folder Link(s): AMC6821

AMC6821 データシート(PDF) 13 Page - Texas Instruments

AMC6821 データシート(HTML) 13 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

データシートダウンロード