PCF8566 Просмотр технического описания (PDF) - Philips Electronics
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PCF8566 Datasheet PDF : 40 Pages
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Philips Semiconductors
Universal LCD driver for low multiplex
rates
Product specification
PCF8566
6.1 Power-on reset
At power-on the PCF8566 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.
6.2 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.
6.3 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 ≥ 3 Vth. 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
( 3 = 1.732 for 1 : 3 multiplex or 21 ⁄ 3 = 1.528 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):
Vop = 6Vop(mrs) = 2.449Voff (rms)
1 : 4 multiplex (1⁄2bias):
Vop = 4 3 ⁄ 3Voff (rms) = 2.309Voff (rms)
These compare with Vop = 3 Voff(rms) when 1⁄3bias is used.
Table 2 Preferred LCD drive modes: summary of characteristics
LCD DRIVE MODE
Static (1 BP)
1 : 2 MUX (2 BP)
1 : 2 MUX (2 BP)
1 : 3 MUX (3 BP)
1 : 4 MUX (4 BP)
LCD BIAS
CONFIGURATION
static (2 levels)
1⁄2 (3 levels)
1⁄3 (4 levels)
1⁄3 (4 levels)
1⁄3 (4 levels)
V-----o---Vf-f---(o--r-pm----s---)-
0
2 ⁄ 4 = 0.354
1⁄3 = 0.333
1⁄3 = 0.333
1⁄3 = 0.333
V-----o--V-n---(-o-r-p-m----s---)
1
10 ⁄ 4 = 0.791
5 ⁄ 3 = 0.745
33 ⁄ 9 = 0.638
3 ⁄ 3 = 0.577
D = V-V----oo---fn-f--(-(-r-r-mm----ss---))-
∞
5 = 2.236
5 = 2.236
33 ⁄ 3 = 1.915
3 = 1.732
1998 May 04
7
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