PCF8820U Philips Semiconductors, PCF8820U Datasheet - Page 45

• Manufacturer Part Number: PCF8820U
• Description: 67 x 101 Grey-scale/ECB colour dot matrix LCD driver
• Manufacturer: Philips Semiconductors

Philips Semiconductors
13.3
The high voltage generator contains a voltage multiplier
which uses a charge pump circuit supplied by V
V
factor from 2 to 8. In the direct drive mode the output
voltage V
When the charge pump is used the total supply current of
the PCF8820 at a supply voltage of 3, 4 and 5 V is shown
in Figs 27, 28 and 29.
The separate graphs are shown for each voltage multiplier
factor with the following conditions:
2000 Dec 07
handbook, full pagewidth
DD3
At T
V
supply
Supply line resistors of 50
Internal clock not calibrated
No LCD connected to the PCF8820
All pixels defined at grey-scale level 32; this is the worst
case
Bias system
Full screen mode (bit PS = 0) at a multiplex rate of 1 : 67
Normal display mode.
67 101 Grey-scale/ECB colour dot matrix
LCD driver
I DD(tot)
DD1
(mA)
. The multiplier is software programmable with a
amb
1.2
1.0
0.8
0.6
0.4
0.2
High voltage generator
, V
0
LCDOUT
4
DD2
and V
x 2
1
9
= V
5
DD3
DD2
.
connected to the same power
6
x 3
(typical value)
Fig.27 Charge pump characteristics for V
7
8
DD2
x 4
9
and
45
10
The characteristics shown for each voltage multiplier
factor are terminated before V
the maximum value to indicate that the voltage cannot be
increased any further. If a higher voltage is required, a
higher voltage multiplier factor must be selected.
Connecting a LCD may increase the current into
pad V
charge pump and also its efficiency. The amount of current
load may depend on the type of LCD used.
It is advisable to evaluate the PCF8820 connected to the
desired LCD and set to the required mode(s) to produce
characteristics similar to Figs 27, 28 and 29. The
customer can then use these graphs to select the most
efficient and safe voltage multiplier factor for each mode
required.
x 5
LCDIN
11
which may affect the current taken by the
12
DD
= 3 V.
13
x 6
x 8
x 7
programmed V LCDOUT (V)
LCDOUT
14
Product specification
has been reached
15
PCF8820
MGT132
16