Driver holtek HT1620

[Calamar]

Some one worked with ht162x??
My circuit board is like the showed in
HT1620 datasheet, page 11 rev 1.20
but the Vlcd is not enought with the
the 3Meg resistor, using a 680K
resistor (instead 3Meg) the Vlcd
reach almost 4.0V is it the way
to increase de Vlcd voltage ?
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)

[Humberto]

Hola Calamar.

I never used this display, but regarding your question I found the following
info in the Holtek documentation:

http://www.holtek.com.tw/english/tech/faq/RAMlcd_faq.htm

"The problem of uneven illumination of LCD pixels can be caused
by insufficient drive current from the LCD driver, this can be resolved in 2 ways:

By using LCD panels with a COM-SEG capacitance value of less than 10pf, reducing
the size of the pixels and choosing higher quality displays are all measures
which can be used to increase impedance and reduce the loading effects of the
application circuit.

Increase the current drive of the HT1650/1660/1670

Increase VLCD, which will increase the Vrms-on and Vrms-off window, which will
increase the light/dark contrast.

Choose a large Bias Current.

Choosing a suitable resistor value (about 1K) to be placed between the pins
VDD -T1, T1-T2, T2-T3, T3-T4, T4-T000 and T000-VSS etc and choosing a suitable
capacitance value (about 0.1uF) to be placed between the pins T1-VSS andT4-VSS
will reduce the output impedance and increase the drive current capability of the device. "

Hope this help you,

saludos

Humberto

[Calamar]

Thank you Humberto, but the info don't match with the
HT1620. There is any way to paste the
circuit in the post ? I would like post the schematic,
may be some one with experience over lcd drivers
and charge pump could give me a cloud...
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)

[Humberto]

[Calamar]

yes my problem is poor LCD contrast, I change
the r=3Megohm value because the data sheet
dont specify what to do,, where did say that instead
it I should change the value capacitor conected in
CC1/CC2 ?
My glass LCD work with 4.Xv and the MCU is a
MSP430 power a litium cell so I choice the HT1620
because it has a charge pump.

Where are your from (city) ?

Saludos Daniel
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)

[Humberto]

Holtek HT1620 Datasheet (I have more than 4 versions, the last is from July, 1999)
Page 2:

Notes: CS: Chip selection
BZ, BZ: Tone outputs
WR, RD, DATA: Serial interface
COM0~COM3, SEG0~SEG31: LCD outputs
IRQ: Time base or WDT overflow output
VO15N: Half voltage circuit output pin
VEE: Double voltage circuit output pin
CC1/CC2: External capacitor pin, for double voltage and half voltage circuit use

If you want to contact me pls. use the private msg option.

Saludos,

Humberto