ADE7569 datasheet(101/144 Pages) AD

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ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 101 of 144

VOLTAGE GENERATION

LCD EXTERNAL CIRCUITRY

The ADE7566/ADE7569/ADE7166/ADE7169 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/ADE7166/

ADE7169. 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.

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

When selecting how to generate the LCD waveform voltages,

the following should be considered:

Figure 89.

LCDVC

LCDVB

LCDVA

LCDVP1

LCDVP2

CHARGE PUMP

AND

LCD WAVEFORM

CIRCUITRY

100nF

470nF

•

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.

Figure 89. 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

generated on-chip, the LCD bias compensation implemented to

maintain contrast over temperature and supply is not possible.

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/ADE7166/

ADE7169 temperature and supply voltage measurements (see

the

The external circuitry needed for the resistor ladder option is

shown in Figure 90. 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

Temperature, Battery, and Supply Voltage Measurements

section). This dynamic contrast control is not easily

implemented with external resistor ladder voltage generation.

Figure 90. External Circuitry for External Resistor Ladder Option

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

charge pump provides the LCD waveform voltages. The ADE7566/

ADE7569/ADE7166/ADE7169 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

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 90).

Note that the internal voltage reference must be enabled by

setting the REF_BAT_EN bit in the Peripheral Configuration

SFR (PERIPH, 0xF4) to allow LCD operation in PSM2 (see

Table 80.

Lifetime Performance

Table 19).

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.

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