PIC16LC925T-I/CL View Datasheet(PDF) - Microchip Technology
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Description
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PIC16LC925T-I/CL Datasheet PDF : 182 Pages
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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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