AN3110 STMICROELECTRONICS | Alldatasheet

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January 2010 Doc ID 16799 Rev 1 1/10 AN3110 Application note Using the STVM100 to automatically adjust VCOM voltage in e-paper Introduction The widespread use of multimedia electronic devices, coupled with environmental concerns over the manufacturing and use of traditional paper products, provide the opportunity for the utilization of electronic paper (e-paper). Electronic paper is the best replacement for conventional paper. A high-quality image can be displayed for weeks without power. Energy is consumed only during the short refresh time. Unlike its counterpart, liquid crystal display (LCD) devices, e-paper does not require a backlight, which not only saves energy, but also makes reading more comfortable. Achieving high-quality images on e-paper requires the correct setting of the VCOM voltage on the PC board. STMicroelectronics offers the STVM100 VCOM calibrator which is ideal for e-paper applications and allows the VCOM voltage to be set automatically. In this application note, the e-paper principle is briefly described so that the user can understand the necessity of an accurate VCOM voltage setting and how the STVM100 can be used for this purpose.

1 General principle of e-paper

even though there is no power applied to the e-paper. by pixels with the active matrix controlled using TFT (Thin-Film Transistor) technology. Figure 1. E-paper display layout

2 E-paper VCOM calibration using the STVM100

–2.5 V, but this range varies according to the technology. replace the mechanical potentiometer as an automatic, more accurate, and robust solution. the basic connection of the STVM100 in e-paper applications. Figure 3. STVM100 and VCOM buffer (TS512 from ST) on e-paper PC board which is applied to the VCOM plate of the e-paper.

  • The STVM100 replaces the conventional variable resistor (VR). The STVM100 is robust, accurate, easily configurable, and provides automatic adjustment capability.
  • The TS512 supports ±18 V (here ±15 V is used) which is necessary in e-paper applications.
  • No additional supply is required, making the power management circuit design easier. VDD5 AVDD 2 Vout 1 Vset 8 GND 4WP3 SCL7 SDA6 STVM100 +3V3 80.6K +15V 28K 100K R12 14K GND -15V SDA SCL VCOM+ VCOM- 1OUT1 1IN-2 1IN+3 VDD-4 2IN+ 52IN- 62OUT 7VDD+ 8 TS512 VCOM- BUFVset 0 GND TP 5 TP 8 TP 6 -15V +15V R14 R15 +3V3 Not mounted AM04748v1

3 STVM100 auto-adjustment demonstration kit

demonstration kit to facilitate calibration. comparison and confirmation of the VCOM value. Figure 4. VCOM auto-adjustment kit GUI

4 Auto-adjustment demonstration kit test results

Table 1 gives an example of the lab test results of the auto-adjustment kit. the e-book VCOM application. Table 1. Test results of the auto-adjustment kit

the e-book. Please refer to Figure 3 for a detailed description. Table 1. Test results of the auto-adjustment kit (continued)

5 Conclusion

The STVM100 VCOM calibrator is ideally suited for the e-paper and e-book display applications. By taking advantage of its 7-bit, non-volatile common voltage setting capability, it allows easy and automated configuration of e-book display panels in a manufacturing environment. An STVM100 auto-adjustment kit is also available to demonstrate how VCOM accuracy of better than ±16 mV is easily achievable.

6 Revision history

Table 2. Document revision history 07-Jan-2010 1 Initial release.