PCF8578 View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
PCF8578 Datasheet PDF : 48 Pages
| |||
Philips Semiconductors
LCD row/column driver for
dot matrix graphic displays
Product specification
PCF8578
7.3 Multiplexed LCD bias generation
The bias levels required to produce maximum contrast
depend on the multiplex rate and the LCD threshold
voltage (Vth). Vth is typically defined as the RMS voltage at
which the LCD exhibits 10% contrast. Table 2 shows the
optimum voltage bias levels for the PCF8578 as functions
of Vop (Vop = VDD − VLCD), together with the discrimination
ratios (D) for the different multiplex rates. A practical value
for Vop is obtained by equating Voff(rms) with Vth. Figure 4
shows the first 4 rows of Table 2 as graphs. Table 3 shows
the relative values of the resistors required in the
configuration of Fig.5 to produce the standard multiplex
rates.
Table 2 Optimum LCD voltages
PARAMETER
MULTIPLEX RATE
1 : 8 1 : 16 1 : 24 1 : 32
V--V---o-2--p
0.739 0.800 0.830 0.850
V--V---o-3--p
0.522 0.600 0.661 0.700
V--V---o-4--p
0.478 0.400 0.339 0.300
V--V---o-5--p
0.261 0.200 0.170 0.150
V-----o--V-f-f--(o--r-pm-----s--)
0.297 0.245 0.214 0.193
V-----o--V-n--(-o-r--pm----s---)
0.430 0.316 0.263 0.230
D = V-V----oo---fn-f--((-r-r-mm----s-s--))
1.447 1.291 1.230 1.196
V-V----ot--h-p
3.370 4.080 4.680 5.190
7.4 Power-on reset
At power-on the PCF8578 resets to a defined starting
condition as follows:
1. Display blank
2. 1 : 32 multiplex rate, row mode
3. Start bank, 0 selected
4. Data pointer is set to X, Y address 0, 0
5. Character mode
6. Subaddress counter is set to 0
7. I2C-bus interface is initialized.
Data transfers on the I2C-bus should be avoided for 1 ms
following power-on, to allow completion of the reset action.
1.0
V bias
Vop
0.8
0.6
MSA838
V2
V3
0.4
V4
0.2
V5
0
1:8
1:16
1:24
1:32
multiplex rate
Vbias = V2, V3, V4, V5. See Table 2.
Fig.4 Vbias/Vop as a function of the multiplex rate.
Table 3 Multiplex rates and resistor values for Fig.5
RESISTORS
R1
R2
R3
MULTIPLEX RATE (n)
n=8
R
( n – 2)R
(3 – n)R
n = 16, 24, 32
R
R
( n – 3)R
2003 Apr 14
9
Share Link: 