PIC16LC925T-I/CL 查看數據表（PDF） - Microchip Technology

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PIC16LC925T-I/CL

64/68-Pin CMOS Microcontrollers with LCD Driver

Microchip Technology 

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

CPCLK

VGEN

Control

Logic

VDD

3

10 µA

Regulator

3 2C

2

C

3

2

C+ VGEN

VGEN

VLCDADJ

100 kΩ*

130 kΩ*

VLCD3

VLCD2

VLCD1

0.47 µF*

0.47 µF*

0.47 µF*

10 kΩ*

VLCD3

10 kΩ*

10 kΩ*

VLCD3

VLCD2

VLCD1

VLCD0

To

LCD

Drivers

C1 C2

0.47 µF*

Connections for

internal charge

pump, VGEN = 1

5 kΩ*

Connections for

external R-ladder,

1/3 Bias,

VGEN = 0

VLCD3

10 kΩ*

5 kΩ*

Connections for

external R-ladder,

Static Bias,

VGEN = 0

* These values are provided for design guidance only and should be optimized to the application by the designer.

 2001 Microchip Technology Inc.

Preliminary

DS39544A-page 95

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