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Segment LCD drivers
Introduction
Segment Liquid Crystal Display (LCD) drivers are used to drive numbers, starburst alphanumeric characters, and icons in today's products.
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Key advantages of segment-driven LCD displays are low communication overhead, low power, and virtually limitless but fixed display configurations.
NXP segment LCD display drivers contain RAM to store the contents of the display.
The display contents is communicated to the LCD segment driver over a bus such as the I2C bus.
The segment display driver contains sequencing logic and backplane and segment drivers.
NXP LCD segment drivers require no external components.
The segment drivers can be used individually or in combination with other display driver types.
For a meter, you could have a bar graph with additional cursors on the bottom, above, and on either end, along with a 3 digit 7-segment portion, and with a variety of units signs: μA, °CI.
For segment displays, any module technology can be used.
NXP segment drivers are available in almost any package configuration:
- Surface mount TSSOP and QFP packages can connect to the display cell by a flex foil or elastomer zebra connection.
- With Chip-On-board (COB), the LCD driver die is bonded (aluminum or gold) to the printed circuit board and then covered by a glob top to protect it. The display cell can be attached the same way as with surface mount packages. The advantage of COB is a lower mechanical height resulting in slimmer modules.
- With Chip-On-glass (COG), the LCD driver die is mounted by ACF technology by the glass vendor directly next to the display area, resulting in the slimmest form factor.
All three module types can easily be back-lit by LEDs.
A suitable and recommended universal driver is our NXP PCA9633 which allows color-changing backlights.
Features
NXP segment LCD drivers are available with world-class features:
On-Chip RAM
On-Chip RAM holds the display contents and avoids high bus traffic to refresh the display some 60 times per second.
The power consumption to access internal RAM is much lower than via external buses.
All NXP LCD drivers feature internal RAM.
Blinker Capability
The segment drivers PCF8533, PCF8534A, PCF8562, PCF8566, and PCF8576(C,D) have a built-in blinking feature with 2 different modes.
In one mode, the whole display blinks, or if a 2:1 or 1:1 multiplex is used, a section of the display can be blinked (RAM-banks are alternated).
Additionally, two blinking frequencies can be selected: 1Hz or 2Hz.
The built-in blinking feature saves CPU power.
Low-Power Consumption
The power consumption of liquid crystal displays is, by nature, very low.
It is a passive display technology, where the available light is either blocked or not.
NXP Semiconductors selects semiconductor processes with the lowest leakage performance possible, thereby cutting power consumption down to the best in the industry.
Cascade Operation
To control displays with larger numbers of segments, LCD drivers can be cascaded.
With two or more chips synchronized, backplanes are common, guaranteeing uniform display appearance.
Our PCF8566, PCF8562, PCF8576C, PCF8576D, PCF8533, and PCF8534A allow cascading with multiple units of the same type.
Auto-Incremental Addressing
With auto-incremental addressing, writing to the display RAM can be done by just setting the starting address then following with data.
The address is incremented automatically.
This feature also allows the updating of only a desired section, saving CPU usage and using less power consumption due to lower interface traffic.
In cascaded arrangements, the auto-increment pointer for the address functions across chip boundaries.
Power-On Reset
When first supplying power to the LCD driver, the interface and control logic are reset automatically.
The display RAM however is not cleared.
We suggest clearing the RAM during initialization prior to enabling the display.
All NXP LCD drivers have this feature.
LCD Bias Generator
Multiplexing the display (thereby saving connections to the display cell) requires distinct voltage levels between VLCD and ground.
These so called bias levels are generated on chip.
All NXP LCD drivers (except the PCF8578) have this feature.
LCD Voltage Selector
These days, digital controls are semi-standardized at certain voltages: 5V, 3.3V, 2.7V, 2.4V, 1.8V.
At the same time, however, each liquid crystal (LC) has a specific driving voltage, depending upon the optimum contrast, speed, and temperature.
Therefore, a separate input VLCD is used.
Some liquid crystals are available for VLCD = 3.3V or 5V, allowing a reduction in power supply circuit overhead.
For these liquid crystals, the VLCD can be connected to the supply pin.
Internal or External Clocks
In order to minimize required external components, NXP's LCD drivers include an on-chip oscillator.
In some sensitive applications, designers prefer to have control over all the frequencies and harmonics in the system.
In these cases, a specific frequency can be supplied by an external clock.
For most applications, however, the internal clock is best to use.
Products
Comparison Table
Multiplexing is a scheme used to reduce the number of connections to the display cell.
40 to 80 connections to the glass can be hardly managed.
On the other hand, liquid crystal optical performance (contrast and viewing angle) degrades with higher mux rates.
For low multiplex rates of 1 to 4, possibly up to 8, liquid crystal displays of TN type are commonly used.
For higher multiplex rates greater than 4 to 8, so-called STN ones are a better choice.
| Product | Number of Segments at Multiplex Rates | Interface | IDD (μA) |
VDD | VLCD | Package(s) | |||||||
| 1:1 | 1:2 | 1:3 | 1:4 | 1:8 | 1:16 | 1:24 | 1:32 | ||||||
| PCF2100C | 40 | CBUS | 20 | 2.25 - 6 | 2.25 - 6 | SO-28 | |||||||
| PCF2111C | 64 | CBUS | 20 | 2.25 - 6 | 2.25 - 6 | VSO-40 | |||||||
| PCF2112C | 32 | CBUS | 20 | 2.25 - 6 | 2.25 - 6 | DIL-40, VSO-40 | |||||||
| OM4068 | 32 | 64 | 96 | SPI | 12 | 2.5 - 5.5 | 3.5 - 6.5 | QFP-44, Bare Die in Tray |
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| PCF8577C | 32 | 64 | 100kHz I2C | 25 | 2.5 - 6 | 2.5 - 6 | DIL-40, VSO-40, Bare Die in FFC |
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| PCF8566 | 24 | 48 | 72 | 96 | 100kHz I2C | 30 | 2.5 - 6 | 2.5 - 6 | DIL-40, VSO-40, Bare Die in Tray |
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| PCF8562 | 32 | 64 | 96 | 128 | 400kHz I2C | 8 | 1.8 - 5.5 | 2.5 - 6.5 | TSSOP-48 | ||||
| PCF8576 | 40 | 80 | 120 | 160 | 100kHz I2C | 90 | 2 - 9 | 2 - 9 | VSO-56 | ||||
| PCF8576C | 40 | 80 | 120 | 160 | 100kHz I2C | 40 | 2 - 6 | 2 - 6 | VSO-56, LQFP-64, HTSSOP-56, Bare Die in Tray Gold-Bumped Die in Tray Bare Die in FFC |
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| PCF8576D | 40 | 80 | 120 | 160 | 400kHz I2C | 8 | 1.8 - 5.5 | 2.5 - 6.5 | TSSOP-56, TQFP-64 Bare Die in Tray Gold-Bumped Die in Tray |
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| PCF8534A | 60 | 120 | 180 | 240 | 400kHz I2C | 8 | 1.8 - 5.5 | 2.5-6.5 | LQFP-80, Bare Die in Tray |
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| PCF8533 | 80 | 160 | 240 | 320 | 400kHz I2C | 8 | 1.8 - 5.5 | 2.5 - 6.5 | Gold-Bumped Die in Tray | ||||
| PCF85133 | 80 | 160 | 240 | 320 | 400kHz I2C | 8 | 1.8 - 5.5 | 2.5 - 6.5 | Gold-Bumped Die in Tray | ||||
| PCF8532 | 160 | 320 | 480 | 640 | 400kHz I2C | 4 | 1.8 - 5.5 | 2.5 - 6.5 | Gold-Bumped Die in Tray | ||||
| PCF8578 | 256 | 384 | 384 | 256 | 100kHz I2C | 6 or 20 | 2.5 - 6 | 3.5 - 9 | VSO-56, TQFP-64, Bare Die in FFC |
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| PCF8579 | Expansion Driver for PCF8578 | 100kHz I2C | 9 | 2.5 - 6 | 3.5 - 9 | VSO-56, TQFP-64, Bare Die in FFC |
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The PCF8578 graphic LCD driver can be used as a very large segment LCD driver or a combination graphics and segment LCD driver.
Further, the PCF8579 LCD column expansion driver can be used to expand the maximum number of segments of the PCF8578 in increments of up to 32 x 40 and/or expand the number of columns of LCD graphics in increments of 40.
Segment LCD Drivers
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