ADM8840 Просмотр технического описания (PDF) - Analog Devices

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ADM8840

Charge Pump Regulator & COM Driver for Color TFT Panel

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADM8840

Pin

Mnemonic

PIN FUNCTION DESCRIPTION (Contd.)

Function

19

20,21

23

29,28

25,24

27,26

30

ADD_OUT

C5+,C5-

+15VOUT

C4+,C4-

C3+,C3-

C2+,C2-

-15VOUT

Voltage Adder Output Pin. This is voltage generated by adding VOUT

(unregulated output of first stage doubler) to VCC. This summed voltage is

then used as the supply for the gain stage which generates the Level

Translator Output Voltage. A 4.7␮F capacitor is recommended for this pin.

External capacitor C5 is connected between these pins. A 3.3␮F capacitor is

recommended.

+15.0V output pin. This was derived by tripling the +5.0V regulated output. A

0.22␮F capacitor is required on this pin.

External capacitor C4 is connected between these pins. A 0.22␮F capacitor is

recommended.

External capacitor C3 is connected between these pins. A 0.22␮F capacitor is

recommended.

External capacitor C2 is connected between these pins. A 0.22␮F capacitor is

recommended.

-15.0V output pin. This was derived by inverting the +15.0V output. A

0.22␮F capacitor is required on this pin.

COM_OUT VOLTAGE

The COM Driver section of the ADM8840 can be used to

generate the alternate frame or line inversion of the COM

line of the LCD panel. The ADM8840 receives the COM

clock (with frequency up to 10kHz) from the controller and

allows programmable conditioning of its amplitude and

centre voltage through the use of on-board DAC’s 1 and 2.

This allows programmable elimination of display flicker

caused by the COM inversion.

The COM_OUT amplitude can be programmed from 4.0V

to 7.0V in steps of 28mV. The COM_OUT centre voltage

can be programmed from 0.9V to 2.8V in steps of 14mV.

Figure 1 below shows a typical output from the COM_OUT

pin. If programmable operation is not required the DACs can

be shutdown with the DAC1_SD and DAC2_SD pins and an

analog voltage applied to the DAC1_IN and DAC2_IN pins

to set up the amplitude and centre voltage at COM_OUT.

POWER SEQUENCING

In order for the TFT panel to power up correctly, the gate

drive supplies must be sequenced such that the -15V supply

starts up before the +15V supply. The ADM8840 controls

this sequence. When the device is turned on, the ADM8840

allow the -15V output to ramp immediately, but holds off the

+15V output. It continues to do this until the negative output

has reached -3V. At this point, the positive output is enabled

and allowed to ramp to +15V. This sequence is highlighted

in figure 2.

tDEL AY1

VCC

SHDN

tR5V

90%

+5V

tF5V

10%

4.0Vto7.0V

0V

0.9V->1.8V->2.8V

+15V

-15V

tR15V

90%

10%

tDELAY2

90%

-3V

10%

tFM15V

tF 15V

tRM15V

Figure 1. COM_OUT Voltage

A MP L ITUDE :

4 .0V to 7 .0V

COM_OUT

0V

CENTR E

V O LT AG E:

0.9 V ->1.8 V->2.8 V

Figure 2. Power Sequence

–6–

REV. PrG 2/03

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