поискавой системы для электроныых деталей |
|
ADM1028ARQ датащи(PDF) 8 Page - Analog Devices |
|
ADM1028ARQ датащи(HTML) 8 Page - Analog Devices |
8 / 16 page REV. A ADM1028 –8– TEMPERATURE MEASUREMENT SYSTEM Internal Temperature Measurement The ADM1028 contains an on-chip bandgap temperature sen- sor. The on-chip ADC performs conversions on the output of this sensor and outputs the temperature data in 8-bit two’s complement format. The format of the temperature data is shown in Table I. Table I. Temperature Data Format Temperature Digital Output –128 °C 1000 0000 –125 °C 1000 0011 –100 °C 1001 1100 –75 °C 1011 0101 –50 °C 1100 1110 –25 °C 1110 0111 –1 °C 1111 1111 0 °C 0000 0000 +1 °C 0000 0001 +10 °C 0000 1010 +25 °C 0001 1001 +50 °C 0011 0010 +75 °C 0100 1011 +100 °C 0110 0100 +125 °C 0111 1101 +127 °C 0111 1111 External Temperature Measurement The ADM1028 can measure the temperature of an external diode sensor or diode-connected transistor, connected to Pins 9 and 10. Pins 9 and 10 are a dedicated temperature input channel. The default functions of Pins 11 and 12 are as THERM outputs to indicate over-temperature conditions. The forward voltage of a diode or diode-connected transistor, operated at a constant current, exhibits a negative temperature coefficient of about –2 mV/ °C. Unfortunately, the absolute value of VBE varies from device to device, and individual calibration is required to null this out, making the technique unsuitable for mass production. The technique used in the ADM1028 is to measure the change in VBE when the device is operated at two different currents. This is given by: ∆VBE = KT/q × ln(N) where: K is Boltzmann’s constant. q is charge on the carrier. T is absolute temperature in Kelvins. N is ratio of the two currents. Figure 3 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, provided for tempera- ture monitoring on some microprocessors, but it could equally well be a discrete transistor. If a discrete transistor is used, the collector will not be grounded, and should be linked to the base. If a PNP transistor is used, the base is connected to the D– input and the emitter to the D+ input. If an NPN transistor is used, the emitter is connected to the D– input and the base to the D+ input. To prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D– input. If the sensor is used in a very noisy environment, a capacitor of value up to 1000 pF may be placed between the D+ and D– inputs to filter the noise. To measure ∆VBE, the sensor is switched between operating currents of I and N × I. The resulting waveform is passed through a 65 kHz low-pass filter to remove noise, thence to a chopper-stabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to ∆VBE. This voltage is measured by the ADC to give a temperature output in 8-bit two’s complement format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. An external temperature measurement nominally takes 9.6 ms. LOW-PASS FILTER fC = 65kHz BIAS DIODE REMOTE SENSING TRANSISTOR IN IIBIAS D+ D– VOUT+ VOUT– TO ADC VDD Figure 3. Signal Conditioning LAYOUT CONSIDERATIONS Digital boards can be electrically noisy environments, and care must be taken to protect the analog inputs from noise, particu- larly when measuring the very small voltages from a remote diode sensor. The following precautions should be taken: 1. Place the ADM1028 as close as possible to the remote sens- ing diode. Provided that the worst noise sources such as clock generators, data/address buses and CRTs are avoided, this distance can be 4 to 8 inches. 2. Route the D+ and D– tracks close together, in parallel with grounded guard tracks on each side. Provide a ground plane under the tracks if possible. 3. Use wide tracks to minimize inductance and reduce noise pickup. Ten mil track minimum width and spacing is rec- ommended. 4. Try to minimize the number of copper/solder joints, which can cause thermocouple effects. Where copper/solder joints are used, make sure that they are in both the D+ and D– path and at the same temperature. Thermocouple effects should not be a major problem as 1 °C corresponds to about 200 µV, and thermocouple voltages are about 3 µV/oC of temperature difference. Unless there are two thermocouples with a big temperature differential between them, thermocouple voltages should be much less than 200 µV. 5. Place 0.1 µF bypass and 2200 pF input filter capacitors close to the ADM1028. 6. If the distance to the remote sensor is more than 8 inches, the use of twisted-pair cable is recommended. This will work up to about 6 to 12 feet. |
Аналогичный номер детали - ADM1028ARQ |
|
Аналогичное описание - ADM1028ARQ |
|
|
ссылки URL |
Конфиденциальность |
ALLDATASHEETRU.COM |
Вашему бизинису помогли Аллдатащит? [ DONATE ] |
Что такое Аллдатащит | реклама | контакт | Конфиденциальность | обмен ссыками | поиск по производителю 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 |