INTEDG datasheet(344/478 Pages) MICROCHIP

344 / 478 page

PIC16(L)F1946/47

DS41414D-page 344

 2010-2012 Microchip Technology Inc.

27.5

LCD Bias Internal Reference

Ladder

The internal reference ladder can be used to divide the

LCD bias voltage two or three equally spaced voltages

that will be supplied to the LCD segment pins. To create

this, the reference ladder consists of three matched

resistors. Refer to Figure 27-3.

27.5.1

BIAS MODE INTERACTION

When in 1/2 Bias mode (BIASMD = 1), then the middle

resistor of the ladder is shorted out so that only two

voltages are generated. The current consumption of the

ladder is higher in this mode, with the one resistor

removed.

TABLE 27-3:

LCD INTERNAL LADDER

POWER MODES (1/3 BIAS)

27.5.2

POWER MODES

The internal reference ladder may be operated in one of

three power modes. This allows the user to trade off LCD

contrast for power in the specific application. The larger

the LCD glass, the more capacitance is present on a

physical LCD segment, requiring more current to

maintain the same contrast level.

Three different power modes are available, LP, MP and

HP. The internal reference ladder can also be turned off

for applications that wish to provide an external ladder

or to minimize power consumption. Disabling the

internal reference ladder results in all of the ladders

being disconnected, allowing external voltages to be

supplied.

Whenever the LCD module is inactive (LCDA = 0), the

internal reference ladder will be turned off.

Power

Mode

Nominal Resistance of

Entire Ladder

Nominal

IDD

Low

3 Mohm

1 µA

Medium

300 kohm

10 µA

High

30 kohm

100 µA

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