PIC16C926-I/CL Microchip Technology, PIC16C926-I/CL Datasheet - Page 97

• Manufacturer Part Number: PIC16C926-I/CL
• Description: 64/68-Pin CMOS Microcontrollers with LCD Driver
• Manufacturer: Microchip Technology

11.5
There are two methods for LCD voltage generation:
internal charge pump, or external resistor ladder.
11.5.1
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 V
FIGURE 11-9:
2001 Microchip Technology Inc.
* These values are provided for design guidance only and should be optimized to the application by the designer.
V
DD
100 k *
VLCDADJ
130 k *
Voltage Generation
Regulator
10 A
CHARGE PUMP
CHARGE PUMP AND RESISTOR LADDER
V
V
LCD
LCD
CPCLK
VGEN
3
V
0.47 F*
3
3
LCD
10 k *
LCD
3
1 on the charge
2
V
0.47 F*
LCD
10 k *
10 k *
Preliminary
2
3
Control
3
Logic
2
V
0.47 F*
C
C
LCD
pump. The charge pump boosts V
2*V
pump is not operating, Vlcd3 will be internally tied to
V
charge pump capacitor and potentiometer values.
11.5.2
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.
DD
2
1
LCD
. See the Electrical Specifications section for
10 k *
1 and V
C+ VGEN
EXTERNAL R-LADDER
VGEN
PIC16C925/926
LCD
3 = 3 * V
0.47 F*
C1
5 k *
5 k *
LCD
C2
1. When the charge
LCD
V
V
V
V
Connections for
internal charge
pump, VGEN = 1
Connections for
external R-ladder,
1/3 Bias,
VGEN = 0
Connections for
external R-ladder,
Static Bias,
VGEN = 0
DS39544A-page 95
LCD
LCD
LCD
LCD
1 into V
3
2
1
0
To
LCD
Drivers
LCD
2 =