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AD7865BS-2 データシート(PDF) 10 Page - Analog Devices |
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AD7865BS-2 データシート(HTML) 10 Page - Analog Devices |
10 / 19 page REV. B AD7865 –10– CIRCUIT DESCRIPTION Analog Input Section The AD7865 is offered as three part types, the AD7865-1 where each input can be configured for ±10 V or a ±5 V input voltage range, the AD7865-3 which handles input voltage range ±2.5 V and the AD7865-2 which has an input voltage range of 0 V to 2.5 V or 0 V to 5 V. The amount of current flowing into the analog input will depend on the analog input range and the analog input voltage. The maximum current flows when negative full scale is applied. AD7865-1 Figure 2 shows the analog input section of the AD7865-1. Each input can be configured for ±5 V or ±10 V operation on the AD7865-1. For ±5 V operation, the V INxA and VINxB inputs are tied together and the input voltage is applied to both. For ±10 V operation, the VINxB input is tied to AGND and the input volt- age is applied to the VINxA input. The VINxA and VINxB inputs are symmetrical and fully interchangeable. Thus for ease of PCB layout on the ±10 V range, the input voltage may be applied to the VINxB input while the VINxA input is tied to AGND. AD7865-1 VINxA TRACK/ HOLD TO ADC REFERENCE CIRCUITRY TO INTERNAL COMPARATOR R4 R1 R2 6k 2.5V REFERENCE R3 GND VINxB VREF Figure 2. AD7865-1 Analog Input Structure For the AD7865-1, R1 = 4 k Ω, R2 = 16 kΩ, R3 = 16 kΩ and R4 = 8 k Ω. The resistor input stage is followed by the high input impedance stage of the track/hold amplifier. The designed code transitions take place midway between suc- cessive integer LSB values (i.e., 1/2 LSB, 3/2 LSBs, 5/2 LSBs etc.) LSB size is given by the formula, 1 LSB = FSR/16384. For the ±5 V range, 1 LSB = 10 V/16384 = 610.4 µV. For the ±10 V range, 1 LSB = 20 V/16384 = 1.22 mV. Output coding is twos complement binary with 1 LSB = FSR/16384. The ideal input/ output transfer function for the AD7865-1 is shown in Table I. Table I. Ideal Input/Output Code Table for the AD7865-1 Analog Input 1 Digital Output Code Transition +FSR/2 – 3/2 LSB 2 011 . . . 110 to 011 . . . 111 +FSR/2 – 5/2 LSB 011 . . . 101 to 011 . . . 110 +FSR/2 – 7/2 LSB 011 . . . 100 to 011 . . . 101 AGND + 3/2 LSB 000 . . . 001 to 000 . . . 010 AGND + 1/2 LSB 000 . . . 000 to 000 . . . 001 AGND – 1/2 LSB 111 . . . 111 to 000 . . . 000 AGND – 3/2 LSB 111 . . . 110 to 111 . . . 111 –FSR/2 + 5/2 LSB 100 . . . 010 to 100 . . . 011 –FSR/2 + 3/2 LSB 100 . . . 001 to 100 . . . 010 –FSR/2 + 1/2 LSB 100 . . . 000 to 100 . . . 001 NOTES 1FSR is full-scale range and is 20 V for the ±10 V range and 10 V for the ±5 V range, with VREF = 2.5 V. 21 LSB = FSR/16384 = 1.22 mV ( ±10 V—AD7865-1) and 610.4 mV (±5 V— AD7865-1) with VREF = 2.5 V. AD7865-2 Figure 3 shows the analog input section of the AD7865-2. Each input can be configured for 0 V to 5 V operation or 0 V to 2.5 V operation. For the 0 V to 5 V operation, the VINxB input is tied to AGND and the input voltage is applied to VINxA input. For 0 V to 2.5 V operation, the VINxA and VINxB inputs are tied together and the input voltage is applied to both. The VINxA and VINxB inputs are symmetrical and fully interchangeable. Thus for ease of PCB layout on the 0 V to 5 V range the input voltage may be applied to the VINxB input while the VINxA input is tied to AGND. For the AD7865-2, R1 = 4 k Ω and R2 = 4 kΩ. Once again, the designed code transitions occur on successive integer LSB values. Output coding is straight (natural) binary with 1 LSB = FSR/16384 = 2.5 V/16384 = 0.153 mV, and 5 V/16384 = 0.305 mV, for 0 V to 2.5 V and 0 V to 5 V options respectively. Table II shows the ideal input and output transfer function for the AD7865-2. AD7865-2 VINxA TRACK/ HOLD TO ADC REFERENCE CIRCUITRY TO INTERNAL COMPARATOR R1 6k 2.5V REFERENCE R2 VINxB VREF Figure 3. AD7865-2 Analog Input Structure Table II. Ideal Input/Output Code Table for the AD7865-2 Analog Input 1 Digital Output Code Transition +FSR/2 – 3/2 LSB 2 111 . . . 110 to 111 . . . 111 +FSR/2 – 5/2 LSB 111 . . . 101 to 111 . . . 110 +FSR/2 – 7/2 LSB 111 . . . 100 to 111 . . . 101 AGND + 5/2 LSB 000 . . . 010 to 000 . . . 011 AGND + 3/2 LSB 000 . . . 001 to 000 . . . 010 AGND – 1/2 LSB 000 . . . 000 to 000 . . . 001 NOTES 1FSR is full-scale range and is 0 V to 2.5 V and 0 V to 5 V for AD7865-2 with VREF = 2.5 V. 21 LSB = FSR/16384 and is 0.153 mV (0 V to 2.5 V) and 0.305 mV (0 V to 5 V) for AD7865-2) with VREF = 2.5 V. |
同様の部品番号 - AD7865BS-2 |
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同様の説明 - AD7865BS-2 |
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