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OM4085T Datasheet(PDF) 6 Page - NXP Semiconductors |
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OM4085T Datasheet(HTML) 6 Page - NXP Semiconductors |
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6 / 36 page  1997 Feb 25 6 Philips Semiconductors Product specification Universal LCD driver for low multiplex rates OM4085 Power-on reset At power-on the OM4085 resets to a defined starting condition as follows: 1. All backplane outputs are set to VDD 2. All segment outputs are set to VDD 3. The drive mode ‘1 : 4 multiplex with 1 ⁄3bias’ is selected 4. Blinking is switched off 5. Input and output bank selectors are reset (as defined in Table 5) 6. The I2C-bus interface is initialized 7. The data pointer and the subaddress counter are cleared. Data transfers on the I2C-bus should be avoided for 1 ms following power-on to allow completion of the reset action. LCD bias generator The full-scale LCD voltage (Vop) is obtained from VDD − VLCD. The LCD voltage may be temperature compensated externally through the VLCD supply to pin 12. Fractional LCD biasing voltages are obtained from an internal voltage divider of three series resistors connected between VDD and VLCD. The centre resistor can be switched out of circuit to provide a 1 ⁄2bias voltage level for the 1 : 2 multiplex configuration. LCD voltage selector The LCD voltage selector coordinates the multiplexing of the LCD according to the selected LCD drive configuration. The operation of the voltage selector is controlled by MODE SET commands from the command decoder. The biasing configurations that apply to the preferred modes of operation, together with the biasing characteristics as functions of Vop =VDD − VLCD and the resulting discrimination ratios (D), are given in Table 2. A practical value of Vop is determined by equating Voff(rms) with a defined LCD threshold voltage (Vth), typically when the LCD exhibits approximately 10% contrast. In the static drive mode a suitable choice is Vop ≥ 3Vth. Multiplex drive ratios of 1 : 3 and 1 : 4 with 1 ⁄2 bias are possible but the discrimination and hence the contrast ratios are smaller ( for 1 : 3 multiplex or for 1 : 4 multiplex). The advantage of these modes is a reduction of the LCD full scale voltage Vop as follows: 1 : 3 multiplex (1 ⁄2bias): 1 : 4 multiplex (1 ⁄2bias): These compare with Vop =3Voff(rms) when 1⁄3bias is used. 3 1.732 = 21 3 ⁄ 1.528 = V op 6V op(mrs) 2.449V off rms () = = V op 3 4 3 ⁄ V off rms () 2.309V off rms () == Table 2 Preferred LCD drive modes: summary of characteristics LCD DRIVE MODE LCD BIAS CONFIGURATION Static (1 BP) static (2 levels) 0 1 ∞ 1 : 2 MUX (2 BP) 1 ⁄2 (3 levels) 1 : 2 MUX (2 BP) 1 ⁄3 (4 levels) 1 ⁄3 = 0.333 1 : 3 MUX (3 BP) 1 ⁄3 (4 levels) 1 ⁄3 = 0.333 1 : 4 MUX (4 BP) 1 ⁄3 (4 levels) 1 ⁄3 = 0.333 V off rms () V op ----------------------- V on rms () V op ----------------------- D V on rms () V off rms () ----------------------- = 2 4 0.354 = ⁄ 10 4 ⁄ 0.791 = 52.236 = 53 ⁄ 0.745 = 52.236 = 33 9 ⁄ 0.638 = 33 3 ⁄ 1.915 = 33 ⁄ 0.577 = 31.732 = |
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