PCF8820 datasheet(45/60 Pages) PHILIPS

45 / 60 page

2000 Dec 07

Philips Semiconductors

Product speciﬁcation

× 101 Grey-scale/ECB colour dot matrix

LCD driver

PCF8820

13.3

High voltage generator

The high voltage generator contains a voltage multiplier

which uses a charge pump circuit supplied by VDD2 and

VDD3. The multiplier is software programmable with a

factor from 2 to 8. In the direct drive mode the output

voltage VLCDOUT =VDD2.

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 Tamb

• VDD1, VDD2 and VDD3 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 1⁄9

• 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 VLCDOUT 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 VLCDIN 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.

handbook, full pagewidth

1.2

programmed VLCDOUT (V)

IDD(tot)

(mA)

45678

913

MGT132

0.8

0.4

1.0

0.6

0.2

x 8

x 2

x 3

x 4

x 5

x 7

x 6

Fig.27 Charge pump characteristics for VDD =3V.

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