ZHCSV99C February 1997 – October 2024 XTR105
PRODUCTION DATA
Many applications require adjustment of initial errors. Input offset and reference current mismatch errors can be corrected by adjustment of the zero resistor, RZ. Adjusting the gain-setting resistor, RG, corrects any errors associated with gain.
Table 7-2 shows how to calculate the effect of various error sources on the circuit accuracy. A sample error calculation for a typical RTD measurement circuit (Pt100 RTD, 200°C measurement span) is provided. The results reveal the XTR105 excellent accuracy, in this case 1.1% unadjusted. Adjusting resistors RG and RZ for gain and offset errors improves circuit accuracy to 0.32%. These are worst-case errors; maximum values were used in the calculations and all errors were assumed to be positive (additive). The XTR105 achieves performance that is difficult to obtain with discrete circuitry and requires less space.
| SAMPLE ERROR CALCULATION | ||||
|---|---|---|---|---|
| RTD value at 4mA output (RRTD MIN): 100Ω | ||||
| RTD measurement range: 200°C | ||||
| Ambient temperature range (ΔΤΑ): 20°C | ||||
| Supply voltage change (ΔV+): 5V | ||||
| Common-mode voltage change (ΔCM): 0.1V | ||||
| ERROR SOURCE | ERROR EQUATION | SAMPLE ERROR CALCULATION(1) | ERROR (ppm of Full Scale) |
|
| UNADJ. | ADJUST. | |||
| INPUT | ||||
| Input offset voltage | VOS / (VIN MAX) × 106 | 100μV / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 1645 | 0 |
| vs common-mode | CMRR · ΔCM/(VIN MAX) × 106 | 50μV/V × 0.1V / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 82 | 82 |
| Input bias current | IB / IREF × 106 | 0.025μΑ / 800μΑ × 106 | 31 | 0 |
| Input offset current | IOS× RRTD MIN / (VIN MAX) × 106 | 3nA × 100Ω / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 5 | 0 |
| Total Input Error: | 1763 | 82 | ||
| EXCITATION | ||||
| Current reference accuracy | IREF accuracy (%) / 100% × 106 | 0.2% / 100% × 106 | 2000 | 0 |
| vs supply | (IREF vs V+) × ΔV+ | 25ppm/V × 5V | 125 | 125 |
| Current reference matching | IREF matching (%) / 100% × 800μA × RRTD MIN / (VIN MAX) × 106 | 0.1% / 100% × 800μΑ × 100Ω / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 1316 | 0 |
| vs supply | (IREF matching vs V+) × ΔV+ × RRTD MIN / (VIN MAX) | 10ppm/V × 5V × 800μΑ × 100Ω / (800μΑ × 0.38Ω/°C × 200°C) | 66 | 66 |
| Total Excitation Error: | 3507 | 191 | ||
| GAIN | ||||
| Span | Span error (%) / 100% × 106 | 0.2% / 100% × 106 | 2000 | 0 |
| Nonlinearity | Nonlinearity (%) / 100% × 106 | 0.01% / 100% × 106 | 100 | 100 |
| Total Gain Error: | 2100 | 100 | ||
| OUTPUT | ||||
| Zero output | (IZERO – 4mA) / 16000μΑ × 106 | 25μΑ / 16000μΑ × 106 | 1563 | 0 |
| vs supply | (IZERO vs V+) × ΔV+ / 16000μΑ × 106 | 0.2μΑ/V × 5V / 16000μΑ × 106 | 63 | 63 |
| Total Output Error: | 1626 | 63 | ||
| DRIFT (ΔTA = 20°C) | ||||
| Input offset voltage | Drift × ΔTA / (VIN MAX) × 106 | 1.5μV/°C × 20°C / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 493 | 493 |
| Input bias current (typical) | Drift × ΔΤΑ / 800μΑ × 106 | 20pA/°C × 20°C / 800μA × 106 | 0.5 | 0.5 |
| Input offset current (typical) | Drift × ΔΤΑ × RRTD MIN / (VIN MAX) × 106 | 5pA/°C × 20°C × 100W / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 0.2 | 0.2 |
| Current reference accuracy | Drift · ΔΤΑ | 35ppm/°C × 20°C | 700 | 700 |
| Current reference matching | Drift × ΔΤΑ × 800μΑ × RRTD MIN / (VIN MAX) | 15ppm/°C × 20°C × 800μΑ × 100Ω / (800μΑ × 0.38Ω/°C × 200°C) | 395 | 395 |
| Span | Drift × ΔΤΑ | 25ppm/°C × 20°C | 500 | 500 |
| Zero output | Drift × ΔΤΑ / 16000μΑ × 106 | 0.5μΑ/°C × 20°C / 16000μΑ × 106 | 626 | 626 |
| Total Drift Error: | 2715 | 2715 | ||
| NOISE (0.1Hz to 10Hz, typical) | ||||
| Input offset voltage | vn / (VIN MAX) × 106 | 0.6μV / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 10 | 10 |
| Current reference | IREF noise × RRTD MIN / (VIN MAX) × 106 | 3nA × 100Ω / (800μΑ × 0.38Ω/°C × 200°C) × 106 | 5 | 5 |
| Zero output | IZERO noise / 16000μA × 106 | 0.03μΑ / 16000μΑ × 106 | 2 | 2 |
| Total Noise Error: | 17 | 17 | ||
| TOTAL ERROR: | 11728 (1.17%) | 3168 (0.32%) | ||