4.1 LCD Charge Pump VLCD3 vs. VDD

The LCD panel being driven by the code snippet from Example 4-1 is a 5.0V piece of glass, however the board in this application was designed to be powered by 3 AAA batteries with a regulated VDD voltage of 3.3V. The integrated LCD charge pump is an excellent choice for this type of application as it can boost the VDD supply voltage to generate the necessary bias voltages for the LCD. Figure 4.1 below compares VLCD3 versus VDD as VDD is swept from 1.0V to 5.0V. The graph shows that the integrated LCD charge pump is capable of boosting VDD up to the configured bias voltage (VLCD3) even as the supply drops close to 2.0V. This makes the integrated LCD charge pump ideal for battery powered applications, and helps ensure that the contrast of the display does not degrade as the batteries lose charge over time. Without the LCD charge pump, VLCD3 would decrease as the batteries lose charge over time directly affecting the contrast of the display.

Info: The LCD module was configured to operate in Low-Power (Low-Current) mode for Example 4-1. The Charge Pump drops off around 2.0V in Figure 4-1, but in applications where the LCD Charge Pump is configured to operate in Normal Current mode (LPEN = 0), the charge pump may work for a wider range of VDD voltages.
Figure 4-1. Figure 4-1: VDD vs. VLCD with LCD Charge Pump Enabled