LTC1605 APPLICATIONS INFORMATION Internal Voltage Reference is adjusted until the output code is changing between 0111 The LTC1605 has an on-chip, temperature compensated, 1111 1111 1110 and 0111 1111 1111 1111. Figure 6 shows curvature corrected, bandgap reference, which is factory the bipolar transfer characteristic of the LTC1605. trimmed to 2.50V. The full-scale range of the ADC is 1 equal to (±4 • V 10V INPUT VIN REF) or nominally ±10V. The output of the 2 200Ω AGND1 reference is connected to the input of a unity-gain buffer 1% through a 4k resistor (see Figure 3). The input to the buffer + 2.2μF 33.2k LTC1605 3 or the output of the reference is available at REF (Pin 3). 1% REF 4 CAP The internal reference can be overdriven with an external + 2.2μF reference if more accuracy is needed. The buffer output 5 AGND2 drives the internal DAC and is available at CAP (Pin 4). The 1605 • F04 CAP pin can be used to drive a steady DC load of less than Figure 4. ±10V Input Without Trim 2mA. Driving an AC load is not recommended because it can cause the performance of the converter to degrade. 1 10V INPUT V 2 IN 200Ω AGND1 1% 4k + 2.2μF REF 3 BANDGAP 3 (2.5V) REFERENCE 33.2k REF 1% 5V LTC1605 2.2μF + VANA 576k R4 50k + 4 CAP – R3 2.2μF 50k 5 CAP 4 AGND2 (2.5V) 1605 • F05 INTERNAL 2.2μF CAPACITOR Figure 5. ±10V Input with Offset and Gain Trim DAC 1605 • F03 011...111 011...110 BIPOLAR Figure 3. Internal or External Reference Source ZERO 000...001 For minimum code transition noise the REF pin and the 000...000 CAP pin should each be decoupled with a capacitor to 111...111 filter wideband noise from the reference and the buffer OUTPUT CODE 111...110 (2.2µF tantalum). 100...001 FS = 20V Offset and Gain Adjustments 100...000 1LSB = FS/65536 The LTC1605 offset and full-scale errors have been trimmed –FS/2 –1 0V 1 FS/2 – 1LSB LSB LSB at the factory with the external resistors shown in Figure 4. INPUT VOLTAGE (V) 1605 • F06 This allows for external adjustment of offset and full scale in Figure 6. LTC1605 Bipolar Transfer Characteristics applications where absolute accuracy is important. See Figure DC Performance 5 for the offset and gain trim circuit. First adjust the offset to zero by adjusting resistor R3. Apply an input voltage of One way of measuring the transition noise associated –152.6mV (–0.5LSB) and adjust R3 so the code is changing with a high resolution ADC is to use a technique where between 1111 1111 1111 1111 and 0000 0000 0000 0000. a DC signal is applied to the input of the ADC and the The gain error is trimmed by adjusting resistor R4. An input resulting output codes are collected over a large number voltage of 9.999542V (+FS – 1.5LSB) is applied to VIN and R4 of conversions. For example in Figure 7 the distribution of 1605fd 10 For more information www.linear.com/LTC1605 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Converter Characteristics Analog Input Dynamic Accuracy Internal Reference Characteristics Digital Inputs and Outputs Timing Characteristics Power Requirements Typical Performance Characteristics Pin Functions Test Circuit Functional Block Diagram Applications Information Package Description Revision History Package Description Related Parts
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