PCIF0 datasheet(214/294 Pages) ATMEL

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214

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

However, if the signal is not bipolar by nature (9bits + sign as the 10th bit), this scheme loses

one bit of the converter dynamic range. Then, if the user wants to perform the conversion with

the maximum dynamic range, the user can perform a quick polarity check of the result and use

the unipolar differential conversion with selectable differential input pair. When the polarity

check is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH register). If the

bit is one, the result is negative, and if this bit is zero, the result is positive.

18.9

Temperature Measurement

The temperature measurement is based on an on-chip temperature sensor that is coupled to a

single ended ADC input. MUX[4..0] bits in ADMUX register enables the temperature sensor.

The internal 1.1V voltage reference must also be selected for the ADC voltage reference

source in the temperature sensor measurement. When the temperature sensor is enabled, the

ADC converter can be used in single conversion mode to measure the voltage over the tem-

perature sensor.

The measured voltage has a linear relationship to the temperature as described in Table 18-2.

The voltage sensitivity is approximately 1LSB/°C and the accuracy of the temperature mea-

surement is ±10°C using manufacturing calibration values (TS_GAIN, TS_OFFSET). The

values described in Table 18-2 are typical values. However, due to the process variation the

temperature sensor output varies from one chip to another.

18.9.1

Manufacturing Calibration

Calibration values determined during test are available in the signature row.

The temperature in degrees Celsius can be calculated using the formula:

Where:

ADCH & ADCL are the ADC data registers,

is the temperature sensor gain

TSOFFSET is the temperature sensor offset correction term

TS_GAIN is the unsigned fixed point 8-bit temperature sensor gain factor in

1/128th units stored in the signature row

TS_OFFSET is the signed twos complement temperature sensor offset reading

stored in the signature row. See Table 21-1 on page 232 for signature row

parameter address.

Table 18-2.

Temperature vs. Sensor Output Voltage (Typical Case): Example ADC Values

Temperature/°C

–40°C

+25°C

+85°C

0x00F6

0x0144

0c01B8

ADCH

() ADCL

[]

273

TS_OFFSET

–

()

–

() 128

TS_GAIN

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