Datasheet LTC1400 (Analog Devices) - 10
| Fabricante | Analog Devices |
| Descripción | Complete SO-8, 12-Bit, 400ksps ADC with Shutdown |
| Páginas / Página | 20 / 10 — U U. APPLICATIO S I FOR ATIO. Unipolar/Bipolar Operation and Adjustment. … |
| Formato / tamaño de archivo | PDF / 588 Kb |
| Idioma del documento | Inglés |
U U. APPLICATIO S I FOR ATIO. Unipolar/Bipolar Operation and Adjustment. Figure 8. LTC1400 Unipolar Transfer Characteristics
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LTC1400
U U W U APPLICATIO S I FOR ATIO
trimmed to 2.42V. It is internally connected to the DAC
Unipolar/Bipolar Operation and Adjustment
and is available at Pin 3 to provide up to 1mA of current to Figure 8 shows the ideal input/output characteristics for an external load. For minimum code transition noise, the the LTC1400. The code transitions occur midway between reference output should be decoupled with a capacitor to successive integer LSB values (i.e., 0.5LSB, 1.5LSB, filter wideband noise from the reference (10μF tantalum in 2.5LSB, … FS – 1.5LSB). The output code is straight parallel with a 0.1μF ceramic). The VREF pin can be driven binary with 1LSB = 4.096V/4096 = 1mV. Figure 9 shows with a DAC or other means to provide input span adjust- the input/output transfer characteristics for the bipolar ment in bipolar mode. The VREF pin must be driven to at mode in two’s complement format. least 2.45V to prevent conflict with the internal reference. The reference should not be driven to more than 5V. Figure 6 shows an LT1360 op amp driving the reference 111...111 1LSB = FS 4096 pin. Figure 7 shows a typical reference, the LT1019A-5 111...110 111...101 connected to the LTC1400. This will provide an improved 111...100 drift (equal to the maximum 5ppm/°C of the LT1019A- 5) and a ±4.231V full scale. If VREF is forced lower than 2.42V, the REFRDY bit in the serial data output will be OUTPUT CODE UNIPOLAR ZERO forced to low. 000...011 000...010 5V 000...001 000...000 INPUT RANGE A V 0V 1 ±0.846 • V IN CC FS – 1LSB REF(OUT) LSB INPUT VOLTAGE (V) + 1400 F08 V LTC1400 REF(OUT) ≥ 2.45V LT1360 VREF
Figure 8. LTC1400 Unipolar Transfer Characteristics
– 3Ω 10µF GND V 011...111 SS 011...110 BIPOLAR ZERO –5V 1400 F06 000...001
Figure 6. Driving the VREF with the LT1360 Op Amp
000...000 111...111 OUTPUT CODE 111...110 5V INPUT RANGE ±4.231V 100...001 V (= ±0.846 • V A CC REF) IN 100...000 10V LTC1400 –FS/2 –1 0V 1 FS/2 – 1LSB VIN LSB LSB VOUT VREF INPUT VOLTAGE (V) 11400 F09 3Ω LT1019A-5
Figure 9. LTC1400 Bipolar Transfer Characteristics
10µF GND GND VSS –5V
Unipolar Offset and Full-Scale Error Adjustments
1400 F07 In applications where absolute accuracy is important,
Figure 7. Supplying a 5V Reference Voltage to the LTC1400 with the LT1019A-5
offset and full-scale errors can be adjusted to zero. Figure 10a shows the extra components required for full-scale 1400fa 10
U U W U APPLICATIO S I FOR ATIO
trimmed to 2.42V. It is internally connected to the DAC
Unipolar/Bipolar Operation and Adjustment
and is available at Pin 3 to provide up to 1mA of current to Figure 8 shows the ideal input/output characteristics for an external load. For minimum code transition noise, the the LTC1400. The code transitions occur midway between reference output should be decoupled with a capacitor to successive integer LSB values (i.e., 0.5LSB, 1.5LSB, filter wideband noise from the reference (10μF tantalum in 2.5LSB, … FS – 1.5LSB). The output code is straight parallel with a 0.1μF ceramic). The VREF pin can be driven binary with 1LSB = 4.096V/4096 = 1mV. Figure 9 shows with a DAC or other means to provide input span adjust- the input/output transfer characteristics for the bipolar ment in bipolar mode. The VREF pin must be driven to at mode in two’s complement format. least 2.45V to prevent conflict with the internal reference. The reference should not be driven to more than 5V. Figure 6 shows an LT1360 op amp driving the reference 111...111 1LSB = FS 4096 pin. Figure 7 shows a typical reference, the LT1019A-5 111...110 111...101 connected to the LTC1400. This will provide an improved 111...100 drift (equal to the maximum 5ppm/°C of the LT1019A- 5) and a ±4.231V full scale. If VREF is forced lower than 2.42V, the REFRDY bit in the serial data output will be OUTPUT CODE UNIPOLAR ZERO forced to low. 000...011 000...010 5V 000...001 000...000 INPUT RANGE A V 0V 1 ±0.846 • V IN CC FS – 1LSB REF(OUT) LSB INPUT VOLTAGE (V) + 1400 F08 V LTC1400 REF(OUT) ≥ 2.45V LT1360 VREF
Figure 8. LTC1400 Unipolar Transfer Characteristics
– 3Ω 10µF GND V 011...111 SS 011...110 BIPOLAR ZERO –5V 1400 F06 000...001
Figure 6. Driving the VREF with the LT1360 Op Amp
000...000 111...111 OUTPUT CODE 111...110 5V INPUT RANGE ±4.231V 100...001 V (= ±0.846 • V A CC REF) IN 100...000 10V LTC1400 –FS/2 –1 0V 1 FS/2 – 1LSB VIN LSB LSB VOUT VREF INPUT VOLTAGE (V) 11400 F09 3Ω LT1019A-5
Figure 9. LTC1400 Bipolar Transfer Characteristics
10µF GND GND VSS –5V
Unipolar Offset and Full-Scale Error Adjustments
1400 F07 In applications where absolute accuracy is important,
Figure 7. Supplying a 5V Reference Voltage to the LTC1400 with the LT1019A-5
offset and full-scale errors can be adjusted to zero. Figure 10a shows the extra components required for full-scale 1400fa 10