Datasheet LTC1401 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Complete SO-8, 12-Bit, 200ksps ADC with Shutdown |
| Pages / Page | 20 / 10 — APPLICATIONS INFORMATION. UNIPOLAR OPERATION AND ADJUSTMENT. Figure 8. … |
| File Format / Size | PDF / 254 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. UNIPOLAR OPERATION AND ADJUSTMENT. Figure 8. LTC1401 Unipolar Transfer Characteristics
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LTC1401
U U W U APPLICATIONS INFORMATION
is available at Pin 3 to provide up to 1mA current to an
UNIPOLAR OPERATION AND ADJUSTMENT
external load. For minimum code transition noise, the Figure 8 shows the ideal input/output characteristics for reference output should be decoupled with a capacitor to the LTC1401. The code transitions occur midway between filter wideband noise from the reference (10µF tantalum in successive integer LSB values (i.e., 0.5LSB, 1.5LSB, parallel with a 0.1µF ceramic is recommended). The VREF 2.5LSB, ... FS – 1.5LSB ). The output code is straight pin can be driven with a DAC or other means to provide binary with 1LSB = 2.048V/4096 = 0.5mV. input span adjustment. The VREF pin must be driven to at least 1.25V to prevent conflict with the internal reference. The reference should not be driven to more than 3V. 2.048 111...111 1LSB = FS = 4096 4096 111...110 Figure 6 shows an LT1360 op amp driving the reference 111...101 pin. Figure 7 shows a typical reference (LT1634-1.25) 111...100 connected to the LTC1401. This will provide improved drift (equal to the maximum 25ppm/°C of the LT1634- OUTPUT CODE UNIPOLAR 1.25) and a 2.1338V full scale. ZERO 000...011 000...010 3V 000...001 INPUT RANGE 000...000 A V IN CC 1.707 • VREF(OUT) 0V 1 FS – 1LSB LSB + INPUT VOLTAGE (V) LTC1401 LTC1401 • F08 VREF(OUT) ≥ 1.25V LT1360 VREF
Figure 8. LTC1401 Unipolar Transfer Characteristics
– 3Ω 10µF GND
Unipolar Offset and Full-Scale Error Adjustments
LTC1401 • F06 In applications where absolute accuracy is important, the
Figure 6. Driving the VREF with the LT1360 Op Amp
offset and full-scale errors can be adjusted to zero. Offset error must be adjusted before full-scale error. Figure 9a shows the extra components required for full scale error 3V adjustment. If both offset and full-scale adjustments are INPUT RANGE 1.707 • VREF V (= 2.1338V) AIN CC needed, the circuit in Figure 9b can be used. For zero offset 10V error, apply 0.25mV (i.e., 0.5LSB) at the input and adjust LTC1401 V the offset trim until the LTC1401 output code flickers IN VOUT VREF between 0000 0000 0000 and 0000 0000 0001. For zero 3Ω LT1634-1.25 full-scale error, apply an analog input of 2.04725V ( FS – 10µF 1.5LSB or last code transition ) at the input and adjust R5 GND GND until the LTC1401 output code flickers between 1111 1111 LTC1401 • F07 1110 and 1111 1111 1111.
Figure 7. Supplying a 2.5V Reference Voltage to the LTC1401 with the LT1634-1.25
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U U W U APPLICATIONS INFORMATION
is available at Pin 3 to provide up to 1mA current to an
UNIPOLAR OPERATION AND ADJUSTMENT
external load. For minimum code transition noise, the Figure 8 shows the ideal input/output characteristics for reference output should be decoupled with a capacitor to the LTC1401. The code transitions occur midway between filter wideband noise from the reference (10µF tantalum in successive integer LSB values (i.e., 0.5LSB, 1.5LSB, parallel with a 0.1µF ceramic is recommended). The VREF 2.5LSB, ... FS – 1.5LSB ). The output code is straight pin can be driven with a DAC or other means to provide binary with 1LSB = 2.048V/4096 = 0.5mV. input span adjustment. The VREF pin must be driven to at least 1.25V to prevent conflict with the internal reference. The reference should not be driven to more than 3V. 2.048 111...111 1LSB = FS = 4096 4096 111...110 Figure 6 shows an LT1360 op amp driving the reference 111...101 pin. Figure 7 shows a typical reference (LT1634-1.25) 111...100 connected to the LTC1401. This will provide improved drift (equal to the maximum 25ppm/°C of the LT1634- OUTPUT CODE UNIPOLAR 1.25) and a 2.1338V full scale. ZERO 000...011 000...010 3V 000...001 INPUT RANGE 000...000 A V IN CC 1.707 • VREF(OUT) 0V 1 FS – 1LSB LSB + INPUT VOLTAGE (V) LTC1401 LTC1401 • F08 VREF(OUT) ≥ 1.25V LT1360 VREF
Figure 8. LTC1401 Unipolar Transfer Characteristics
– 3Ω 10µF GND
Unipolar Offset and Full-Scale Error Adjustments
LTC1401 • F06 In applications where absolute accuracy is important, the
Figure 6. Driving the VREF with the LT1360 Op Amp
offset and full-scale errors can be adjusted to zero. Offset error must be adjusted before full-scale error. Figure 9a shows the extra components required for full scale error 3V adjustment. If both offset and full-scale adjustments are INPUT RANGE 1.707 • VREF V (= 2.1338V) AIN CC needed, the circuit in Figure 9b can be used. For zero offset 10V error, apply 0.25mV (i.e., 0.5LSB) at the input and adjust LTC1401 V the offset trim until the LTC1401 output code flickers IN VOUT VREF between 0000 0000 0000 and 0000 0000 0001. For zero 3Ω LT1634-1.25 full-scale error, apply an analog input of 2.04725V ( FS – 10µF 1.5LSB or last code transition ) at the input and adjust R5 GND GND until the LTC1401 output code flickers between 1111 1111 LTC1401 • F07 1110 and 1111 1111 1111.
Figure 7. Supplying a 2.5V Reference Voltage to the LTC1401 with the LT1634-1.25
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