PCF8820 datasheet(25/60 Pages) PHILIPS

25 / 60 page

2000 Dec 07

Philips Semiconductors

Product speciﬁcation

× 101 Grey-scale/ECB colour dot matrix

LCD driver

PCF8820

Table 5

Programming the required bias system

Table 6

Examples of LCD bias voltages

BS2

BS1

BS0

BS1/2

BIAS SYSTEM

COMMENT

1/11

1/10

1/9

recommended at multiplex rate 1 : 67

1/8

1/7

1/6

1/5

1/4

recommended at multiplex rate 1 : 8

−2

1/2

allows a lower VLCDIN at multiplex rate 1 : 8

BIAS VOLTAGE

LEVEL ON PAD

CALCULATING BIAS

VOLTAGE

BIAS SYSTEM

1/9 (n = 5)

1/4 (n = 0)

1/2 (n = −2)

VLCDOUT

VLCDIN

8/9 × VLCDIN

3/4 × VLCDIN

1/2 × VLCDIN

7/9 × VLCDIN

1/2 × VLCDIN

VSS1

2/9 × VLCDIN

1/2 × VLCDIN

VLCDIN

1/9 × VLCDIN

1/4 × VLCDIN

1/2 × VLCDIN

VSS1

-------------

LCDIN

-------------

LCDIN

-------------

LCDIN

-------------

LCDIN

8.1.5

HIGH VOLTAGE GENERATOR CONFIGURATION

The PCF8820 incorporates a software configurable

voltage multiplier which uses a charge pump circuit

supplied by VDD2 and VDD3. After a reset the voltage

multiplier factor is set to 2 (VLCDOUT =2 × VDD2). Other

voltage multiplier factors are set by bits S2 to S0.

To reduce high current peaks at voltage multiplier start-up,

it is recommended that the voltage multiplier is switched on

using the following procedure:

1. Set bit DM = 1 and bit PD = 1

2. Set multiplication factor to 2 by setting bits S2 to S0 to

logic 0

3. Set register value VOP to the desired value,

bit PRS = 1 and bit HVE = 1

4. Set bit PD = 0, which switches on the charge pump

(at multiplication factor 2)

5. Increment the multiplication factor to the desired value

for VLCDOUT using bits S2 to S0.

8.1.6

TEMPERATURE READ-OUT

The PCF8820 has a built-in temperature sensor. At the

end of a temperature measurement, the sensor writes a

temperature value to the status register. The temperature

value is an 8-bit number represented by bits TR7 to TR0 in

the status register which can be read via the I2C-bus.

To save power, the sensor need only be enabled when a

measurement is required. A measurement is initialized by

setting bit SM = 1 which will be automatically cleared after

5 clock cycles (from internal oscillator or external clock).

The internal oscillator will be initialized and allowed to

warm-up for approximately 2 frame periods, after which a

measurement will be initiated at the start of the next frame

and completing after 2 frames.

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