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TC7211AM データシート(PDF) 6 Page - TelCom Semiconductor, Inc |
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TC7211AM データシート(HTML) 6 Page - TelCom Semiconductor, Inc |
6 / 7 page 6-12 TELCOM SEMICONDUCTOR, INC. BUS COMPATIBLE, 4-DIGIT CMOS DECODER/DRIVER TC7211AM If more than four devices are slaved together, the backplane signal should be derived externally and all TC7211AM devices slaved to it. The external drive signal must drive a high capacitive load with 1 µsec to 2 µsec rise and fall times. The backplane frequency is normally 125 Hz. At lower display ambient temperatures, the frequency may be reduced to compensate for display response time. The on-chip RC oscillator free-runs at approximately 16 kHz. A divide-by 128 circuit provides the125 Hz backplane frequency. The oscillator frequency may be reduced by connecting an external capacitor between the oscillator terminal and V+. (See typical operating characteristics curves.) The free-running oscillator may be overridden (if de- sired) by an external clock. The backplane driver, however, must not be disabled during the external clock’s negative or lOW portion, as this will result in a DC drive component being applied to the LCD, limiting the LCD’s life. To prevent backplane driver disabling, the oscillator input should be driven from the positive supply to no less than one-fifth the supply voltage above ground. A backplane disable signal will not be sensed if the driving signal remains above ground by one-fifth the supply voltage. An alternate method for externally driving the oscillator permits the oscillator input to swing the full supply voltage range. The oscillator input signal duty cycle is skewed so the LOW BASIC OPERATION The TC7211AM drives 4-digit, 7-segment LCDs. This device contains 28 individual segment drivers, a backplane driver, a self-contained oscillator, and a divider chain to generate the backplane signal. The 28 CMOS segment drivers and backplane driver contain ratioed N- and P-channel transistors for identical ON resistance. The equal resistances eliminate the DC output driver component resulting from unequal rise and fall times. This ensures maximum LCD life. The backplane output driver can be disabled by ground- ing the OSCILLATOR input (pin 36). The 28 output segment drivers can therefore be synchronized directly to an input signal at the backplane (BP) terminal (pin 5). Several slave devices may be cascaded to the backplane output of a master device. The backplane signal may also be derived from an external source. These features permit interfacing to single backplane LCDs with characters in multiples of four. Each slave’s backplane input represents a 200pF capacitive load to the master backplane driver (comparable to one additional segment). The number of slave devices drivable by a master device is therefore set by the larger display backplane capacitive load. The master backplane output will drive the display backplane of 16 one-half-inch characters with rise and fall times under 5 µsec. This represents a system with three slave devices and a fourth master device driving the backplane. TYPICAL CHARACTERISTICS 30 25 20 15 10 5 1 234 5 6 7 Operating Supply Current vs Supply Voltage TA= –20°C TA= +70°C TA= +25°C V+ VOLTS 0 LCD DEVICES DISPLAY BLANK PIN 36 OPEN 180 150 120 90 60 30 0 Backplane Frequency vs Supply Voltage COSC = 0 pF V+ VOLTS 12 3 4 5 6 7 COSC = 22 pF COSC = 220 pF (PIN 36 OPEN) TA = +25°C |
同様の部品番号 - TC7211AM |
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同様の説明 - TC7211AM |
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