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PIC16C925T-S/CL 数据表(PDF) 97 Page - Microchip Technology |
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PIC16C925T-S/CL 数据表(HTML) 97 Page - Microchip Technology |
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97 / 182 page  2001 Microchip Technology Inc. Preliminary DS39544A-page 95 PIC16C925/926 11.5 Voltage Generation There are two methods for LCD voltage generation: internal charge pump, or external resistor ladder. 11.5.1 CHARGE PUMP The LCD charge pump is shown in Figure 11-9. The 1.0V - 2.3V regulator will establish a stable base volt- age from the varying battery voltage. This regulator is adjustable through the range by connecting a variable external resistor from VLCDADJ to ground. The poten- tiometer provides contrast adjustment for the LCD. This base voltage is connected to VLCD1 on the charge pump. The charge pump boosts VLCD1 into VLCD2 = 2*VLCD1 and VLCD3 = 3 * VLCD1. When the charge pump is not operating, Vlcd3 will be internally tied to VDD. See the Electrical Specifications section for charge pump capacitor and potentiometer values. 11.5.2 EXTERNAL R-LADDER The LCD module can also use an external resistor lad- der (R-Ladder) to generate the LCD voltages. Figure 11-9 shows external connections for static and 1/3 bias. The VGEN (LCDCON<4>) bit must be cleared to use an external R-Ladder. FIGURE 11-9: CHARGE PUMP AND RESISTOR LADDER Control Logic 3 2 C CPCLK 2 C 3 2 C+ VGEN 3 VGEN VDD Regulator VGEN VLCD3 VLCD2 VLCD1 VLCD0 To LCD Drivers Connections for internal charge pump, VGEN = 1 VLCD3 VLCD3 Connections for external R-ladder, 1/3 Bias, VGEN = 0 Connections for external R-ladder, Static Bias, VGEN = 0 0.47 µF* 0.47 µF* 0.47 µF* 0.47 µF* 10 k Ω* 10 k Ω* 10 k Ω* 5k Ω* 5k Ω* 10 k Ω* 130 k Ω* 100 k Ω* C2 VLCD2 VLCD1 VLCD3C1 VLCDADJ * These values are provided for design guidance only and should be optimized to the application by the designer. 10 µA |
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