ADE7566 datasheet(92/136 Pages) AD

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ADE7566/ADE7569

Preliminary Technical Data

Rev. PrA | Page 92 of 136

VOLTAGE GENERATION

The ADE7566/ADE7569 provide two ways to generate the LCD

waveform voltage levels. The on-chip charge pump option can

generate 5 V. This makes it possible to use 5 V LCDs with the

3.3 V ADE7566/ADE7569. There is also an option to use an

external resistor ladder with a 3.3 V LCD. The EXTRES bit in

the LCD Configuration X SFR (LCDCONX, 0x9C) selects the

resistor ladder or charge pump option.

When selecting how to generate the LCD waveform voltages,

the following should be considered:

•

Lifetime performance power consumption

•

Contrast control

Lifetime Performance Power Consumption

In most LCDs, a high amount of current is required when the LCD

waveforms change state. The external resistor ladder option draws a

constant amount of current, whereas the charge pump circuitry

allows dynamic current consumption. If the LCD module is used

with the internal charge pump option when the display is disabled,

the voltage generation is disabled, so that no power is consumed by

the LCD function. This feature results in significant power

savings if the display is turned off during battery operation.

Contrast Control

The electrical characteristics of the liquid in the LCD change

over temperature. This requires adjustments in the LCD waveform

voltages to ensure a readable display. An added benefit of the

internal charge pump voltage generation is a configurable bias

voltage that can be compensated over temperature and supply

to maintain contrast on the LCD. These compensations can be

performed based on the ADE7566/ADE7569 temperature and

supply voltage measurements (see the Temperature, Battery, and

Supply Voltage Measurements section). This dynamic contrast

control is not easily implemented with external resistor ladder

voltage generation.

The LCD bias voltage sets the contrast of the display when the

charge pump provides the LCD waveform voltages. The ADE7566/

ADE7569 provide 64 bias levels selected by the BIASLVL bits in

the LCD Configuration X SFR (LCDCONX, 0x9C). The voltage

level on LCDVA, LCDVB and LCDVC depend on the internal

voltage reference value (VREF), BIASLVL[5:0] selection, and the

biasing selected as described in Table 76.

Lifetime Performance

DC offset on a segment degrades its performance over time.

The voltages generated through the internal charge pump

switch faster than those generated by the external resistor

ladder, reducing the likelihood of a dc voltage being applied

to a segment and increasing the lifetime of the LCD.

LCD EXTERNAL CIRCUITRY

The voltage generation selection is made by bit EXTRES in the

LCD Configuration X SFR (LCDCONX, 0x9C). This bit is

cleared by default for charge pump voltage generation, but can

be set to enable an external resistor ladder.

Charge Pump

Voltage generation through the charge pump requires external

capacitors to store charge. The external connections to LCDVA,

LCDVB, and LCDVC, as well as LCDVP1 and LCDVP2, are

shown in Figure 76.

LCDVC

LCDVB

LCDVA

LCDVP1

LCDVP2

CHARGE PUMP

AND

LCD WAVEFORM

CIRCUITRY

100nF

470nF

Figure 76. External Circuitry for Charge Pump Option

External Resistor Ladder

To enable the external resistor ladder option, set the EXTRES

bit in the LCD Configuration X SFR (LCDCONX, 0x9C). When

EXTRES = 1, the LCD waveform voltages are supplied by the

external resistor ladder. Because the LCD voltages are not being

generated on-chip, the LCD bias compensation implemented to

maintain contrast over temperature and supply is not possible.

The external circuitry needed for the resistor ladder option is

shown in Figure 77. The resistors required should be in the

range of 10 kΩ to 100 kΩ and based on the current required by

the LCD being used.

LCDVC

LCDVB

LCDVA

LCDVP1

LCDVP2

LCD WAVEFORM

CIRCUITRY

Figure 77. External Circuitry for External Resistor Ladder Option

LCD FUNCTION IN PSM2

The LCDPSM2 and LCDEN bits in the LCD Configuration SFR

(LCDCON, 0x95) control LCD functionality in the PSM2

operating mode (see Table 86).

Table 86.

LCDPSM2

LCDEN

Result

The display is off in PSM2.

The display is on in PSM2.

The display is off in PSM2.

Note that the LCD configuration and data memory is retained

when the display is turned off.

Example LCD Setup

An example to set up the LCD peripheral for a specific LCD is

described in this section with the following parameters:

•

Type of LCD: 5 V, 4× multiplexed with 1/3 bias, 96 segment

•

Voltage generation: internal charge pump

•

Refresh rate: 64 Hz

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