Moteur de recherche de fiches techniques de composants électroniques |
|
AD7291 Fiches technique(PDF) 8 Page - Analog Devices |
|
AD7291 Fiches technique(HTML) 8 Page - Analog Devices |
8 / 21 page AD7291 Preliminary Technical Data Rev. PrC | Page 8 of 21 ADC TRANSFER FUNCTION The output coding of the AD7291 is straight binary for the analog input channel conversion results and twos complement, for the temperature conversion result. The designed code transitions occur at successive LSB values (that is, 1 LSB, 2 LSBs, and so forth). The LSB size is VREF/4096 for the AD7291. The ideal transfer characteristic for the AD7291 for straight binary coding is shown in Figure 7. 000…000 0V ANALOG INPUT 111…111 000…001 000…010 111…110 • • 111…000 • 011…111 • • 1LSB 1LSB = VREF/4096 +VREF – 1LSB NOTES VREF IS EITHER REFIN OR 2 × REFIN. Figure 7. Straight Binary Transfer Characteristic TEMPERATURE SENSOR OPERATION The AD7291 contains one local temperature sensor. The on- chip, band gap temperature sensor measures the temperature of the AD7291 die. The temperature sensor module on the AD7291 is based on the three current principle (see Figure 8), where three currents are passed through a diode and the forward voltage drop is measured, allowing the temperature to be calculated free of errors caused by series resistance. Figure 8. Top Level Structure of Internal Temperature Sensor The temperature conversion consists of two phases, the integration followed by the conversion. The TSENSE integrates in turn, over a period of one hundred microseconds once the TSENSE bit is selected in the Command Register. This takes place continuously in the background, leaving the user free to perform conversions on the other channels. When integration is complete, a signal passes to the control logic internally to initiate a conversion automatically. It takes a period of approximately100μs to complete the integration and conversion of the temperature result. If the ADC is in command mode, the temperature conversion is performed as soon as the next conversion is completed. In autocycle mode, the conversion is inserted into an appropriate place in the current sequence. If the ADC is idle, the conversion takes place immediately. The TSENSE Result Register stores the result of the last conversion on the temperature channel; these can be read at any time. Theoretically, the temperature measuring circuit can measure temperatures from –512°C to +511°C with a resolution of 0.25°C. However, temperatures outside TA (the specified temperature range for the AD7291) are outside the guaranteed operating temperature range of the device. Temperature Sensor Averaging The AD7291 incorporates a temperature sensor averaging feature to enhance the accuracy of the temperature measurements. The temperature averaging is performed continuously in the background once the TSENSE bit in the command register is enabled. The temperature is measured each time a TSENSE conversion is performed and a moving average method is used to determine the result in the TSENSE Average Result Register. The average result is given by the following equation; ( ) ( ) sult Current sult evious AVG TSENSE Re _ 8 1 Re _ Pr 8 7 _ + = The average result is then available in the TSENSE Average Result Register whose content is updated after every TSENSE conversion. The first TSENSE conversion result given by the AD7291 after the temperature sensor has been selected in the command register (bit D7) is the actual first TSENSE conversion result and this result will remain valid until the next TSENSE conversion is completed and the result register updated. If the status of the TSENSEAVG bit is not changed on successive writes to the command register, the averaging function will not be reinitialized and will continue calculating the cumulative average. If the command register is written to and the content of the TSENSEAVG bit changed the averaging function is reset and the next TSENSE average conversion result is the current temperature conversion result. Temperature Value Format One LSB of the ADC corresponds to 0.25°C. The temperature reading from the ADC is stored in a 12-bit twos complement format, to accommodate both positive and negative temperature measurements. The temperature data format is provided in Table 10. |
Numéro de pièce similaire - AD7291 |
|
Description similaire - AD7291 |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |