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ADS-118A Datasheet(PDF) 4 Page - Murata Power Solutions Inc. |
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ADS-118A Datasheet(HTML) 4 Page - Murata Power Solutions Inc. |
4 / 8 page ADS-118/118A ® ® 4 SIGNAL INPUT GAIN ADJUST 50 Ω To Pin19 of ADS-118A Potentiometer is at 25 Ω during the device's factory trim procedure. 20k Ω –15V (or –5V) +15V (or +5V) To Pin17 of ADS-118A ZERO/ OFFSET ADJUST To Pin19 of ADS-118 –15V SIGNAL INPUT GAIN ADJUST 1.98k Ω 50 Ω +15V 2k Ω 1.2M Ω 20k Ω –15V +15V ZERO/ OFFSET ADJUST CALIBRATION PROCEDURE Any offset and/or gain calibration procedures should not be implemented until devices are fully warmed up. To avoid interaction, offset must be adjusted before gain. The ranges of adjustment for the circuits in Figures 2a and 2b are guaran- teed to compensate for the ADS-118's initial accuracy errors and may not be able to compensate for additional system errors. A/D converters are calibrated by positioning their digital outputs exactly on the transition point between two adjacent digital output codes. This can be accomplished by connecting LED’s to the digital outputs and adjusting until certain LED's "flicker" equally between on and off. Other approaches employ digital comparators or microcontrollers to detect when the outputs change from one code to the next. For the ADS-118, offset adjusting is normally accomplished at the point where the MSB is a 1 and all other output bits are 0’s and the LSB just changes from a 0 to a 1. This digital output transition ideally occurs when the applied analog input is +½LSB (+244μV for ADS-118; +305μV for ADS-118A). Gain adjusting is accomplished when all bits are 1’s and the LSB just changes from a 1 to a 0. This transition ideally occurs when the analog input is at +full scale minus 1½ LSB's (+0.99927V for ADS-118; +1.249085V for ADS-118A). Zero/Offset Adjust Procedure 1. Apply a train of pulses to the START CONVERT input (pin 16) so the converter is continuously converting. 2. Apply +244μV (ADS-118) or +305μV (ADS-118A) to the Table 1. Output Coding for Bipolar Operation +FS –1 LSB +0.99951V 1111 1111 1111 +1.2494V +3/4 FS +0.75000V 1110 0000 0000 +0.9375V +1/2 FS +0.50000V 1100 0000 0000 +0.6250V 0 0.00000V 1000 0000 0000 0.0000V –1/2 FS –0.50000V 0100 0000 0000 –0.6250V –3/4 FS –0.75000V 0010 0000 0000 –0.9375V –FS +1 LSB –0.99951V 0000 0000 0001 –1.2494V –FS –1.00000V 0000 0000 0000 –1.2500V ADS-118 OUTPUT CODING ADS-118A INPUT INPUT BIPOLAR RANGE OFFSET BINARY RANGE SCALE (±1V ) MSB LSB (±1.25V ) ANALOG INPUT (pin 19). 3. Adjust the offset potentiometer until the output bits are 1000 0000 00000 and the LSB flickers between 0 and 1. Gain Adjust Procedure 1. Apply +0.99927V (ADS-118) or +1.249085V (ADS-118A) to the ANALOG INPUT (pin 19). 2. Adjust the gain potentiometer until all output bits are 1's and the LSB flickers between 1 and 0. 3. To confirm proper operation of the device, vary the input signal to obtain the output coding listed in Table 1. Figure 2a. Optional ADS-118 External Gain and Offset Adjust Circuits Figure 2b. Optional ADS-118A Gain and Offset Adjust Circuits |
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