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DAC7741 数据表(PDF) 16 Page - Texas Instruments |
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DAC7741 数据表(HTML) 16 Page - Texas Instruments |
16 / 23 page DAC7741 16 SBAS248B www.ti.com FIGURE 8. Offset Adjustment Transfer Characteristic. OFFSET ADJUSTMENT Offset adjustment is accomplished by introducing a small current into the summing junction (SJ) of the DAC7741. The voltage at SJ, or VSJ, is dependent on the output configura- tion of the DAC7741. See Table IV for the required pin strapping for a given configuration and the nominal values of VSJ for each output range. REFERENCE OUTPUT PIN STRAPPING VSJ(1) CONFIGURATION CONFIGURATION ROFFSET RFB1 RFB2 Internal 0V to +10V to VREF to VOUT to VOUT +5V Reference –10V to +10V NC NC to VOUT +3.333V –5V to +5V to AGND to VOUT to VOUT +1.666V External 0V to VREF to VREF to VOUT to VOUT VREF/2 Reference –VREF to VREF NC NC to VOUT VREF/3 –VREF/2 to VREF/2 to AGND to VOUT to VOUT VREF/6 NOTE: (1) Voltage measured at VSJ for a given configuration. TABLE IV. Nominal VSJ vs. VOUT and Reference Configuration. OUTPUT RPOT2 R1 RS ISJ NOMINAL CONFIGURATION RANGE OFFSET ADJUSTMENT 0V to +10V 10K 0 2.5M ±2µA ±25mV –10V to +10V 10K 5K 1.5M ±2.2µA ±55mV –5V to +5V 10K 20K 1M ±1.7µA ±21mV TABLE V. Recommended External Component Values for Symmetrical Offset Adjustment (VREF = 10V). The current level required to adjust the DAC7741 offset can be created by using a potentiometer divider as shown in Figure 7. Another alternative is to use a unipolar DAC in order to apply a voltage, VOADJ, to the resistor RS. A ±2uA current range applied to SJ will ensure offset adjustment coverage of the ±0.1% maximum offset specification of the DAC7741. When in a unipolar configuration (VSJ = 5V), only a single resistor, RS, is needed for symmetrical offset adjustment with a 0V to 10V VOADJ range. When in one of the two bipolar configurations, VSJ is either +3.333v (±10V range) or +1.666V ( ±5V range), and circuit values chosen to match those given in Table V will provide symmetrical offset adjust. Please refer to Figure 7 for component configuration. OFFSET ADJUST RANGE –10V to +10V V OUT Configuration min (75% of typ) min (75% of typ) typ typ 50 25 0 –25 –50 –22 0 –11 I SJ (µA) 0V to 10V and –5V to +5V V OUT Configuration Figure 8 illustrates the typical and minimum offset adjustment ranges provided by forcing a current at SJ for a given output voltage configuration. GAIN ADJUSTMENT When using the internal reference of the DAC7741, gain adjustment is performed by adjusting the internal refer- ence voltage via the reference adjust pin, REFADJ. The effect of a reference voltage change on the gain of the DAC output can be seen in the generic equation (for unipolar configuration): VOUT = VREFIN • (N/65536) where N is represented in decimal format and ranges from 0 to 65535. REFADJ can be driven by a low impedance voltage source such as a unipolar, 0V to +10V DAC or a potentiometer (less than 100k Ω) as shown in Figure 7. Since the input imped- ance of REFADJ is typically 50k Ω, the smaller the resistance of the potentiometer, the more linear the adjustment will be. A 10k Ω potentiometer is suggested if linearity of the refer- ence adjustment is of concern. REF OUT ADJUST RANGE 40 30 20 10 0 –10 –20 –30 –40 02 4 6 8 10 REFADJ (V) Typical REF OUT Adjustment Range Minimum REF OUT Adjustment Range FIGURE 9. Internal Reference Adjustment Transfer Charac- teristic. VOLTAGE AT REFADJ REFOUT VOLTAGE REFADJ = 0V 10V + 25mV (min) REFADJ = 5V or NC(1) 10V REFADJ = 10V 10V – 25mV (max) NOTE: "NC" is "Not Connected" TABLE VI. Minimum Internal Reference Adjustment Range. When the DAC7741 internal reference is not used, gain adjustments can be made via trimming the external refer- ence applied to the DAC at REFIN. This can be accomplished through using a potentiometer, unipolar DAC, or other means of precision voltage adjustment to control the voltage pre- sented to the DAC7741 by the external reference. Figure 9 and Table VI summarize the range of adjustment of the internal reference via REFADJ. |
类似零件编号 - DAC7741 |
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类似说明 - DAC7741 |
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