STE2004S datasheet(12/79 Pages) STMICROELECTRONICS

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Circuit description

STE2004S

12/79

3.6

LCD voltage generation

The LCD voltage at reference temperature (To = 27°C) can be set using the VOP register content

according to the following formula:

VLCD(T=To) = VLCDo = (Ai+VOP · B)

(i=0,1,2)

with the following values:

Note that the three PRS values produce three adjacent ranges for VLCD. If the VOP register

and PRS bits are set to zero the internal voltage generator is switched off.

The proper value for the VLCD is a function of the liquid crystal threshold voltage (Vth) and

of the multiplexing rate. A general expression for this is:

For MUX Rate m = 65 the ideal VLCD is:

VLCD(to) = 6.85 · Vth

than:

Table 3. Bias level m=65 and m=49

Symbol

m = 65 (1/9)

m = 49 (1/8)

VLCD

8/9*VLCD

7/8*VLCD

7/9*VLCD

6/8*VLCD

2/9*V VLCD

2/8*VLCD

1/9 *VLCD

1/8*VLCD

VSS

Table 4. LCD voltage generation

Symbol

Value

Unit

Note

2.95

PRS = [0;0]

6.83

PRS = [0;1]

10.71

PRS = [1;0]

B0.0303V

°C

LCD

---------

–

⎝⎠

⎛⎞

⋅

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

⋅

6.85

–

⋅

()

0.03

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

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