PIC16C923-04I/CL Microchip Technology, PIC16C923-04I/CL Datasheet - Page 101

• Manufacturer Part Number: PIC16C923-04I/CL
• Description: 8-Bit CMOS Microcontroller with LCD Driver
• Manufacturer: Microchip Technology

13.5
There are two methods for LCD voltage generation,
internal charge pump, or external resistor ladder.
13.5.1
The LCD charge pump is shown in Figure 13-13. 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
pump. The charge pump boosts V
FIGURE 13-13:CHARGE PUMP AND RESISTOR LADDER
1997 Microchip Technology Inc.
V
DD
VLCDADJ
100k*
130k*
Voltage Generation
CHARGE PUMP
* These values are provided for design guidance only and should be
nominal
10 A
optimized to the application by the designer.
V
V
DD
DD
V
0.47 F*
LCD
LCD
10k*
3
LCD
1 on the charge
1 into V
V
0.47 F*
LCD
LCD
10k*
10k*
2
2 =
Charge Pump
V
0.47 F*
LCD
2*V
is not operating, Vlcd3 will be internally tied to V
the Electrical Specifications section for charge pump
capacitor and potentiometer values.
13.5.2
The LCD module can also use an external resistor lad-
der (R-Ladder) to generate the LCD voltages.
Figure 13-13 shows external connections for static and
1/3 bias. The VGEN (LCDCON<4>) bit must be cleared
to use an external R-Ladder.
1
LCD
10k*
1 and V
EXTERNAL R-LADDER
LCD
3 = 3 * V
0.47 F*
C1
PIC16C9XX
5k*
5k*
LCD
C2
1. When the charge pump
DS30444E - page 101
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
SLPEN
LCDEN
DD
. See