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AD7416ARM-REEL датащи(PDF) 9 Page - Analog Devices |
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AD7416ARM-REEL датащи(HTML) 9 Page - Analog Devices |
9 / 20 page REV. G AD7416/AD7417/AD7418 –9– TYPICAL CONNECTION DIAGRAM Figure 2 shows a typical connection diagram for the AD7417. Using the A0, A1, and A2 pins allows the user to select from up to eight AD7417s on the same serial bus, if desired. An external 2.5 V reference can be connected at the REFIN pin. If an exter- nal reference is used, a 10 µF capacitor should be connected between REFIN and GND. SDA and SCL form the 2-wire I 2C compatible interface. For applications where power consump- tion is of concern, the automatic power-down at the end of a conversion should be used to improve power performance. See Operating Modes section of this data sheet. VDD AIN1 GND REFIN SUPPLY 2.7V TO 5.5V 0.1 F 10 F 10 F FOR EXTERNAL REFERENCE OPTIONAL EXTERNAL REFERENCE AD780/ REF-192 0V TO 2.5V INPUT CONVST SDA AIN2 AIN3 AIN4 OTI SCL 2-WIRE SERIAL INTERFACE AD7417 A0 A1 A2 C/ P Figure 2. Typical Connection Diagram ANALOG INPUTS Figure 3 shows an equivalent circuit of the analog input struc- ture of the AD7417 and AD7418. The two diodes, D1 and D2, provide ESD protection for the analog inputs. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 200 mV. This will cause these diodes to become forward-biased and start conducting current into the substrate. The maximum current these diodes can conduct without causing irreversible damage to the part is 20 mA. The capacitor C2 in Figure 3 is typically about 4 pF and can prima- rily be attributed to pin capacitance. The resistor R1 is a lumped component made up of the on resistance of a multiplexer and a switch. This resistor is typically about 1 k Ω. The capacitor C1 is the ADC sampling capacitor and has a capacitance of 3 pF. AIN D1 C1 3pF VDD D2 C2 4pF VBALANCE CONVERT PHASE – SWITCH OPEN TRACK PHASE – SWITCH CLOSED R1 1k Figure 3. Equivalent Analog Input Circuit ON-CHIP REFERENCE The AD7416/AD7417/AD7418 has an on-chip 1.2 V band gap reference that is gained up by a switched capacitor amplifier to give an output of 2.5 V. The amplifier is only powered up at the start of the conversion phase and is powered down at the end of the conversion. The on-chip reference is selected by connecting the REFIN pin to analog ground. This causes SW1 (see Figure 4) to open and the reference amplifier to power up during a conver- sion. Therefore, the on-chip reference is not available externally. An external 2.5 V reference can be connected to the REFIN pin. This has the effect of shutting down the on-chip reference circuitry. 1.2V REFIN SW1 2.5V EXTERNAL REFERENCE DETECT BUFFER 1.2V 26k 24k Figure 4. On-Chip Reference TEMPERATURE MEASUREMENT A common method of measuring temperature is to exploit the negative temperature coefficient of a diode, or the base-emitter voltage of a transistor, operated at a constant current. Unfortu- nately, this technique requires calibration to null out the effect of the absolute value of VBE, which varies from device to device. The technique used in the AD7416/AD7417/AD7418 is to measure the current change in VBE when the device is operated at two different currents. This is given by ∆VKT q n N BE =× () /1 where: K is Boltzmann’s constant. q is the charge on the electron (1.6 × 10-19 Coulombs). T is the absolute temperature in Kelvins. N is the ratio of the two currents. I N I VDD SENSING TRANSISTOR SENSING TRANSISTOR VOUT TO ADC VOUT Figure 5. Temperature Measurement Technique |
Аналогичный номер детали - AD7416ARM-REEL |
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Аналогичное описание - AD7416ARM-REEL |
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