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TC835CKW 数据表(PDF) 10 Page - TelCom Semiconductor, Inc |
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TC835CKW 数据表(HTML) 10 Page - TelCom Semiconductor, Inc |
10 / 12 page 3-74 TELCOM SEMICONDUCTOR, INC. PERSONAL COMPUTER DATA ACQUISITION A/D CONVERTER TC835 Power Supplies and Grounds Power Supplies The TC835 is designed to work from ±5V supplies. For single +5V operation, a TC7660 can provide a – 5V supply. Grounding Systems should use separate digital and analog ground systems to avoid loss of accuracy. Displays and Driver Circuits TelCom Semiconductor manufactures two display de- coder/driver circuits to interface the TC835 to an LCD or LED display. Each drive has 28 outputs for driving four 7-segment digit displays. Device Package Description TC7211AIPL 40-Pin Epoxy 4-Digit LCD Driver/Decoder Several sources exist for LCD and LED display: Display Manufacturer Address Type Hewlett Packard 640 Page Mill Rd. LED Components Palo Alto, CA 94304 Litronix, Inc. 19000 Homestead Rd. LED Cupertino, CA 94010 AND 720 Palomar Ave. LCD and Sunnyvale, CA 94086 LED Epson America, Inc. 3415 Kanhi Kawa St. LCD Torrance, CA 90505 For many dedicated applications where the input signal is always of one polarity, the delay of the comparator need not be a limitation. Since the nonlinearity and noise do not increase substantially with frequency, clock rates of up to ~1 MHz may be used. For a fixed clock frequency, the extra count or counts caused by comparator delay will be a constant and can be subtracted out digitally. The clock frequency may be extended above 200 kHz without this error, however, by using a low-value resistor in series with the integrating capacitor. The effect of the resistor is to introduce a small pedestal voltage on to the integrator output at the beginning of the reference integrate phase. By careful selection of the ratio between this resistor and the integrating resistor (a few tens of ohms in the recommended circuit), the comparator delay can be com- pensated and the maximum clock frequency extended by approximately a factor of 3. At higher frequencies, ringing and second-order breaks will cause significant nonlinearities in the first few counts of the instrument. The minimum clock frequency is established by leakage on the auto-zero and reference capacitors. With most de- vices, measurement cycles as long as 10 seconds give no measurable leakage error. The clock used should be free from significant phase or frequency jitter. Several suitable low-cost oscillators are shown in the applications section. The multiplexed output means that if the display takes significant current from the logic supply, the clock should have good PSRR. Zero-Crossing Flip-Flop The flip-flop interrogates the data once every clock pulse after the transients of the previous clock pulse and half-clock pulse have died down. False zero-crossings caused by clock pulses are not recognized. Of course, the flip-flop delays the true zero-crossing by up to one count in every instance, and if a correction were not made, the display would always be one count too high. Therefore, the counter is disabled for one clock pulse at the beginning of the reference integrate (deintegrate) phase. This one-count delay compensates for the delay of the zero-crossing flip- flop, and allows the correct number to be latched into the display. Similarly, a one-count delay at the beginning of auto-zero gives an overload display of 0000 instead of 0001. No delay occurs during signal integrate, so that true ratiometric readings result. High-Speed Operation The maximum conversion rate of most dual-slope A/D converters is limited by the frequency response of the comparator. The comparator in this circuit follows the inte- grator ramp with a 3 µsec delay, and at a clock frequency of 200 kHz (5 µsec period), half of the first reference integrate clock period is lost in delay. This means that the meter reading will change from 0 to 1 with a 50 µV input, 1 to 2 with 150 µV, 2 to 3 at 250 µV, etc. This transition at midpoint is considered desirable by most users; however, if the clock frequency is increased appreciably above 200 kHz, the instrument will flash "1" on noise peaks even when the input is shorted. |
类似零件编号 - TC835CKW |
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类似说明 - TC835CKW |
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