wanna run LCD at 3.3v

[hayee]

Hi,
I want to operate LCD (NHD-0220DZ-NSW-BBW) at 3.3v.

In the datasheet given:
min input voltage=2.7v
max input voltage=5.5v

Can i use that without having any problem?

[FvM]

The controller operation is no problem, but you should also consider this specification: VDD-V0 = 4.6V (typical), in other words, a contrast pin voltage of about -1.3 V is required. Some LCD displays have an on-board negative voltage generator, but the present device apparently hasn't. If no negative voltage is present in your system, you can use a charge-pump to provide it.

[hayee]

negative voltage will be problem because i have no on board negative supply.
What will be the drawback if i will not use contrast pin,
if i will not use this pin then with which pin i tie contrast pin Vdd or Vss.

[FvM]

[John P]

If you have a pin available on your processor, and enough processing power to generate a square wave, you could create your own charge pump with a couple of capacitors and diodes. No need for any added IC's.

[hayee]

I have also 5v supply in my circuit.So i think better is that i use voltage divider to get 4.6v for contrast option.

[Jerson]

If you have both 3.3V and 5V, let the LCD have the 5V and use it unidirectionally - controller to LCD. Your 3.3V controller can drive the LCD without any problems. Only make sure you NEVER use any of the LCD readback functions. The LCD should be used as a WRITE ONLY device.
_________________
Regards
Jerson Fernandes

[FvM]

I agree, that 5V LCD operation is more easy. Furthermore, you should check, if you are operating the LCD controller at a 5V tolerant IO port of your PIC. Then readback is possible without restrictions.

[hayee]

Thanks guys for your replies.

As far as I understand is that I have to generate a -1.3v by using charge pump circuit and give this -1.3v directly to the contrast pin.

Is it right or not?