ADE7169ASTF16 datasheet(94/140 Pages) AD

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ADE7169F16

Preliminary Technical Data

Rev. PrD | Page 94 of 140

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

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

3.3V ADE7169F16. There is also an option to use an external

resistor ladder with a 3.3V 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:

•

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 will result in significant power savings if the display is

turned off in battery operation.

Contrast control

The electrical characteristics of the liquid in the LCD change

over temperature, requiring 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 ADE7169F16 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

ADE7169F16 provides 64 bias levels selectable using the BLVL

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

voltage level on LCDVA, LCDVB and LCDVC depend on the

the Interntal voltage reference value (Vref), BLVL[5:0] selection

and the biasing selected as described in Table 73.

Lifetime Performance

DC offset on a segment will degrade 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 clear

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 VA, VB,

and VC as well as VP1 and VP2 are shown in LCD

Configuration X SFR (LCDCONX, 0x9C).

LCDVA

LCDVB

LCDVC

LCDVP1

LCDVP2

Charge Pump

and

LCD Waveform

Circuitry

470nF

100nF

Figure 63: 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. Since 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 64. The resistors required should be in the

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

LCD being used.

LCDVA

LCDVB

LCDVC

LCDVP1

LCDVP2

LCD Waveform

Circuitry

Figure 64: External circuitry for External Resistor Ladder option

LCD FUNCTION IN PSM2

The LCDPSM2 bit in the LCD Configuration SFR (LCDCON,

0x95) and the LCDEN bit in the LCD Configuration SFR

ADE7169ASTF16 数据表(PDF) 94 Page - Analog Devices

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