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AD7890SQ-2 Fiches technique(PDF) 9 Page - Analog Devices |
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AD7890SQ-2 Fiches technique(HTML) 9 Page - Analog Devices |
9 / 20 page AD7890 –9– REV. A tions occur on successive integer LSB values (i.e., 1 LSB, 2 LSBs, 3 LSBs . . . ). Output coding is straight (natural) binary with 1 LSB = FS/4096 = 4.096 V/4096 = 1 mV. The ideal input/output transfer function is shown in Table II. +2.5V REFERENCE 2k Ω TO ADC REFERENCE CIRCUITRY 200 Ω* VINX AGND MUX OUT AD7890-4 *EQUIVALENT ON-RESISTANCE OF MULTIPLEXER REF OUT/ REF IN 6k Ω 9.38k Ω Figure 3. AD7890-4 Analog Input Structure Table II. Ideal Input/Output Code Table for the AD7890-4 Digital Output Analog Input 1 Code Transition +FSR – 1 LSB 2 (4.095 V) 111 . . . 110 to 111 . . . 111 +FSR – 2 LSBs (4.094 V) 111 . . . 101 to 111 . . . 110 +FSR – 3 LSBs (4.093 V) 111 . . . 100 to 111 . . . 101 AGND + 3 LSBs (0.003 V) 000 . . . 010 to 000 . . . 011 AGND + 2 LSBs (0.002 V) 000 . . . 001 to 000 . . . 010 AGND + 1 LSB (0.001 V) 000 . . . 000 to 000 . . . 001 NOTES 1FSR is full-scale range and is 4.096 V with REF IN +2.5 V. 21 LSB = FSR/4096 = 1 mV with REF IN = +2.5 V. AD7890-2 The analog input section for the AD7890-2 contains no biasing resistors and the selected analog input connects to the multi- plexer and in cases where MUX OUT is connected to SHA IN this is followed by the high input impedance stage of the track/ hold amplifier. The analog input range is, therefore, 0 V to +2.5 V into a high impedance stage with an input current of less than 50 nA. The designed code transitions occur on successive integer LSB values (i.e., l LSB, 2 LSBs, 3 LSBs . . . FS-1 LSBs). Out- put coding is straight (natural) binary with 1 LSB = FS/4096 = 2.5 V/4096 = 0.61 mV. The ideal input/output transfer function is shown in Table III. Table III. Ideal Input/Output Code Table for the AD7890-2 Digital Output Analog Input 1 Code Transition +FSR – 1 LSB 2 (2.499390 V) 111 . . . 110 to 111 . . . 111 +FSR – 2 LSBs (2.498779 V) 111 . . . 101 to 111 . . . 110 +FSR – 3 LSBs (2.498169 V) 111 . . . 100 to 111 . . . 101 AGND + 3 LSBs (0.001831 V) 000 . . . 010 to 010 . . . 011 AGND + 2 LSBs (0.001221 V) 000 . . . 001 to 001 . . . 010 AGND + 1 LSB (0.000610 V) 000 . . . 000 to 000 . . . 001 NOTES 1FSR is full-scale range and is 2.5 V with REF IN = +2.5 V. 21 LSB = FSR/4096 = 0.61 mV with REF IN = +2.5 V. CIRCUIT DESCRIPTION Analog Input Section The AD7890 is offered as three part types, the AD7890-10 which handles a ±10 V input voltage range, the AD7890-4 which handles a 0 V to +4.096 V input range and the AD7890-2 which handles a 0 V to +2.5 V input voltage range. AD7890-10 Figure 2 shows the analog input section for the AD7890-10. The analog input range for each of the analog inputs is ±10 V into an input resistance of typically 33 k Ω. This input is benign with no dynamic charging currents with the resistor attenuator stage followed by the multiplexer and in cases where MUX OUT is connected to SHA IN this is followed by the high input impedance stage of the track/hold amplifier. The designed code transitions occur on successive integer LSB values (i.e., 1 LSB, 2 LSBs, 3 LSBs...). Output coding is 2s complement binary with 1 LSB – FS/4096 = 20 V/4096 = 4.88 mV. The ideal input/ output transfer function is shown in Table I. +2.5V REFERENCE 2k Ω TO ADC REFERENCE CIRCUITRY 7.5k Ω 30k Ω 200 Ω* 10k Ω VINX AGND MUX OUT AD7890-10 *EQUIVALENT ON-RESISTANCE OF MULTIPLEXER REF OUT/ REF IN Figure 2. AD7890-10 Analog Input Structure Table I. Ideal Input/Output Code Table for the AD7890-10 Digital Output Analog Input 1 Code Transition +FSR/2 – 1 LSB 2 (9.995117 V) 011 . . . 110 to 011 . . . 111 +FSR/2 – 2 LSBs (9.990234 V) 011 . . . 101 to 011 . . . 110 +FSR/2 – 3 LSBs (9.985352 V) 011 . . . 100 to 011 . . . 101 AGND + 1 LSB (0.004883 V) 000 . . . 000 to 000 . . . 001 AGND (0.000000 V) 111 . . . 111 to 000 . . . 000 AGND – 1 LSB (–0.004883 V) 111 . . . 110 to 111 . . . 111 –FSR/2 + 3 LSBs (–9.985352 V) 100 . . . 010 to 100 . . . 011 –FSR/2 + 2 LSBs (–9.990234 V) 100 . . . 001 to 100 . . . 010 –FSR/2 + 1 LSB (–9.995117 V) 100 . . . 000 to 100 . . . 001 NOTES 1FSR is full-scale range and is 20 V with REF IN = +2.5 V. 21 LSB = FSR/4096 = 4.883 mV with REF IN = +2.5 V. AD7890-4 Figure 3 shows the analog input section for the AD7890-4. The analog input range for each of the analog inputs is ± 10 V into an input resistance of typically 15 k Ω. This input is benign with no dynamic charging currents with the resistor attenuator stage followed by the multiplexer and in cases where MUX OUT is connected to SHA IN this is followed by the high input imped- ance stage of the track/hold amplifier. The designed code transi- |
Numéro de pièce similaire - AD7890SQ-2 |
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Description similaire - AD7890SQ-2 |
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