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PCF2113DH Datasheet(PDF) 9 Page - NXP Semiconductors |
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PCF2113DH Datasheet(HTML) 9 Page - NXP Semiconductors |
9 / 72 page 2001 Dec 19 9 Philips Semiconductors Product specification LCD controllers/drivers PCF2113x 7 FUNCTIONAL DESCRIPTION 7.1 LCD supply voltage generator The LCD supply voltage may be generated on-chip. The VLCD generator is controlled by two internal 6-bit registers: VA and VB. The nominal LCD operating voltage at room temperature is given by the relationship: VOP(nom) = (integer value of register × 0.08) + 1.82 7.1.1 PROGRAMMING RANGES Programmed value: 1 to 63. Voltage: 1.90 to 6.86 V. Tref =27 °C. Values producing more than 6.5 V at operating temperature are not allowed. Operation above this voltage may damage the device. When programming the operating voltage the VLCD tolerance and temperature coefficient must be taken into account. Values below 2.2 V are below the specified operating range of the chip and are therefore not allowed. Value 0 for VA and VB switches the generator off (i.e. VA = 0 in character mode, VB = 0 in icon mode). Usually register VA is programmed with the voltage for character mode and register VB with the voltage for icon mode. When VLCD is generated on-chip the VLCD pins should be decoupled to VSS with a suitable capacitor. The generated VLCD is independent of VDD and is temperature compensated. When the VLCD generator and the direct mode are switched off, an external voltage may be supplied at connected pins VLCD1 and VLCD2.VLCD1 and VLCD2 may be higher or lower than VDD2. During direct mode (program DM register bit) the internal VLCD generator is turned off and the VLCD2 output voltage is directly connected to VDD2. This reduces the current consumption during icon mode and Mux 1 : 9 (depending on VDD2 value and LCD liquid properties). The VLCD generator ensures that, as long as VDD is in the valid range (2.2 to 4 V), the required peak voltage VOP = 6.5 V can be generated at any time. 7.2 LCD bias voltage generator The intermediate bias voltages for the LCD display are also generated on-chip. This removes the need for an external resistive bias chain and significantly reduces the system current consumption. The optimum value of VLCD depends on the multiplex rate, the LCD threshold voltage (Vth) and the number of bias levels. Using a 5-level bias scheme for 1 : 18 maximum rate allows VLCD < 5 V for most LCD liquids. The intermediate bias levels for the different multiplex rates are shown in Table 1. These bias levels are automatically set to the given values when switching to the corresponding multiplex rate. Table 1 Bias levels as a function of multiplex rate; note 1 Note 1. The values in the table are given relative to VLCD − VSS, e.g. 3/4 means 3/4 × (VLCD − VSS). MULTIPLEX RATE NUMBER OF LEVELS V1 V2 V3 V4 V5 V6 1:18 5 VLCD 3/4 1/2 1/2 1/4 VSS 1:9 5 VLCD 3/4 1/2 1/2 1/4 VSS 1:2 4 VLCD 2/3 2/3 1/3 1/3 VSS |
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