PCF8820 Datasheet, PDF (45/60 Pages) NXP Semiconductors – 67 x 101 Grey-scale/ECB colour dot matrix LCD driver

Philips Semiconductors
67 × 101 Grey-scale/ECB colour dot matrix
LCD driver
Product specification
PCF8820
13.3 High voltage generator
The high voltage generator contains a voltage multiplier
which uses a charge pump circuit supplied by V_DD2 and
V_DD3. The multiplier is software programmable with a
factor from 2 to 8. In the direct drive mode the output
voltage V_LCDOUT = V_DD2.
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:
• At T_amb
• V_DD1, V_DD2 and V_DD3 connected to the same power
supply
• Supply line resistors of 50 Ω (typical value)
• 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 ¹â„₉
• Full screen mode (bit PS = 0) at a multiplex rate of 1 : 67
• Normal display mode.
The characteristics shown for each voltage multiplier
factor are terminated before V_LCDOUT has been reached
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_LCDIN which may affect the current taken by the
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.
1.2
handbook, full pagewidth
IDD(tot)
(mA)
1.0
0.8
0.6
0.4
0.2
x2
0
4
5
2000 Dec 07
MGT132
x5
x4
x3
x8
x7
x6
6
7
8
9
10
11
12
13
14
15
16
programmed VLCDOUT (V)
Fig.27 Charge pump characteristics for V_DD = 3 V.
45