1 LCD Charge Pump Overview
The LCD charge pump is ideal for low-voltage battery powered applications because it can boost the VDD voltage up using internal circuitry to a level high enough for driving a wide range of LCD panels. When enabled, the charge pump will generate the top level LCD bias voltage (VLCD3) from the VDD source available. In addition to boosting insufficient VDD voltage to drive different displays, the charge pump circuitry can also regulate VDD down to the necessary drive voltage for the display if VDD is too high.
When using the LCD charge pump found on the PIC16(L)F19197 device, it is recommended that a flyback capacitor be connected to the CFLY1 and CFLY2 pins. The purpose of the flyback capacitor is to help with charge storage for the larger LCD loads, and it helps obtain the required voltage boost. In addition to the flyback capacitor should be used, capacitors should be used on each of the VLCDx pins for charge hold and storage to combat the LCD loads associated with larger panels and increased pixel counts. Figure 1-1 shows the functional block diagram for the LCD controller module – this technical brief will discuss what happens within the LCD Bias Generation block of the figure below.