ML9059 datasheet(34/72 Pages) OKI

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PEDL9059-02

OKI Semiconductor

ML9059

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(b) When external resistors are used (voltage V1 adjustment internal resistors are not used)

It is also possible to set the LCD drive power supply voltage V1 without using the internal resistors for voltage V1

adjustment but connecting external resistors (Ra' and Rb') between VSS & VR and between VR & V1. Even in this

case, it is possible to control the LCD power supply voltage V1 and adjust the intensity of LCD display using

commands if the electronic potentiometer function is used.

The voltage V1 can be obtained by the following equation B-1 in the range of V1<VOUT by setting the external

resistors Ra' and Rb' appropriately.

V1 = (1 + (Rb'/Ra'))

• VEV = (1 + (Rb'/Ra')) • (1 – (α/324)) • VREG (Eqn. B-1)

–

VSS

External Ra'

External Rb'

VEV (Constant voltage supply +

electronic potentiometer)

Fig. 10 V1 voltage adjustment circuit (equivalent circuit)

Setting example: Setting V1 = 7 V at Tj = 25°C

When the electronic potentiometer register value is set to the middle value of (DB5, DB4, DB3, DB2, DB1, DB0)

= (1, 0, 0, 0, 0, 0), the value of

α will be 31 and that of VREG will be 3.0 V, and hence the equation B-1 becomes

as follows:

V1 = (1 + (Rb'/Ra'))

• (1 – (α/324)) • VREG

7 = (1 + (Rb'/Ra'))

• (1 – (31/324)) • 3.0 (Eqn. B-2)

Further, if the current flowing through Ra' and Rb' is set as 5 µA, the value of Ra' + Rb' will be - Ra' + Rb' = 1.4

Ω (Eqn. B-3)

and hence,

Rb'/Ra' = 1.58, Ra' = 543 k

Ω, Rb' = 857 kΩ.

In this case, the variability range of voltage V1 using the electronic potentiometer function will be as given in

Table 13.

Table 13 Example 1 of V1 variable-voltage range using electronic potentiometer function

Min

Typ

Max

Unit

Variable-voltage range

6.24 (

α = 63)

7.0 (

α = 31)

7.74 (

α = 0)

[V]

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