PCF8533 Datasheet, PDF (5/45 Pages) NXP Semiconductors – Universal LCD driver for low multiplex rates

NXP Semiconductors
PCF8533
Universal LCD driver for low multiplex rates
6. The I²C-bus interface is initialized.
7. The data pointer and the subaddress counter are cleared (set to logic 0).
8. The display is disabled.
Remark: Do not transfer data on the I²C-bus for at least 1 ms after a power-on to allow
the reset action to complete.
7.2 LCD bias generator
Fractional LCD biasing voltages are obtained from an internal voltage divider of three
series resistors connected between pins V_LCD and V_SS. The center resistor is bypassed
by switch if the ¹â„₂ bias voltage level for the 1:2 multiplex drive mode configuration is
selected.
7.3 LCD voltage selector
The LCD voltage selector coordinates the multiplexing of the LCD in accordance with the
selected LCD drive configuration. The operation of the voltage selector is controlled by the
mode-set command (see Table 10) from the command decoder. The biasing
configurations that apply to the preferred modes of operation, together with the biasing
characteristics as functions of V_LCD and the resulting discrimination ratios (D) are given in
Table 5.
Table 5. Biasing characteristics
LCD drive
mode
Number of:
LCD bias
Backplanes Levels ^{configuration}
static
1
1:2 multiplex 2
1:2 multiplex 2
1:3 multiplex 3
1:4 multiplex 4
2
static
3
1_⁄2
4
1_⁄3
4
1_⁄3
4
1_⁄3
V_{-----o--f--f--(--R---M-----S---)}
V_LCD
0
0.354
0.333
0.333
0.333
-^V----^o--ⁿ---⁽--^R----^M----^S---⁾
V_LCD
1
0.791
0.745
0.638
0.577
D = -^V----^o---ⁿ--⁽--^R----^M----^S----⁾
V_off(RMS)
∞
2.236
2.236
1.915
1.732
A practical value for V_LCD is determined by equating V_off(RMS) with a defined LCD
threshold voltage (V_th), typically when the LCD exhibits approximately 10 % contrast. In
the static drive mode a suitable choice is V_LCD > 3V_th.
Multiplex drive modes of 1:3 and 1:4 with ¹â„₂ bias are possible but the discrimination and
hence the contrast ratios are smaller.
Bias is calculated by -----¹------- , where the values for a are
1+a
a = 1 for ¹â„₂ bias
a = 2 for ¹â„₃ bias
The RMS on-state voltage (V_on(RMS)) for the LCD is calculated with Equation 1:
PCF8533_4
Product data sheet
V_on(RMS)
=
V_LCD
--^a---²----⁺-----²---^a----⁺-----ⁿ---
n × (1 + a)²
where the values for n are
All information provided in this document is subject to legal disclaimers.
Rev. 04 — 5 March 2010
(1)
© NXP B.V. 2010. All rights reserved.
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