ML9050 datasheet(21/71 Pages) OKI

21 / 71 page

¡ Semiconductor

ML9050/9051

21/71

PEDL9050-02

• Voltage adjustment circuit

The voltage multiplier output VOUT produces the LCD drive voltage V1 via the voltage

adjustment circuit. Since the ML9050/9051 incorporates a high accuracy constant voltage

generator,a64-levelelectronicpotentiometerfunction,andalsoresistorsforvoltageV1adjustment,

it is possible to build a high accuracy voltage adjustment circuit with very few components. In

addition, the ML9050/9051 is available in three models with the temperature gradients of - (1)

about -0.05%/˚C, (2) about -0.2%/˚C, and (3) external input (input to pin VRS), as a VREG option.

(a) When the internal resistors for voltage V1 adjustment are used

It is possible to control the LCD power supply voltage V1 and adjust the intensity of LCD display

using commands and without needing any external resistors, if the internal voltage V1 adjustment

resistors and the electronic potentiometer function are used. The voltage V1 can be obtained by

the following equation A-1 in the range of V1<VOUT.

V1 = (1+(Rb/Ra)) • VEV = (1+(Rb/Ra)) • (1–(a/324)) • VREG (Eqn. A-1)

Fig. 9

VREG is a constant voltage generated inside the IC and its value is constant as given in Table 9

at Ta = 25˚C.

–

VSS

Internal Ra

Internal Rb

VEV (Constant voltage generator +

electronic potentiometer)

Fig. 8

*1:

The voltage range of VIN should be set so that the voltage at the pin VOUT does not exceed

the absolute maximum rating.

VOUT = 7 ¥ VIN

= 17.5V

*1 VIN = 2.5 V

VSS = 0 V

VOUT = 6 ¥ VIN

= 18 V

*1 VIN = 3 V

VSS = 0 V

Voltage relationship in 7-times multiplication

Voltage relationship in 6-times multiplication

The voltage relationships in voltage multiplication are shown in Fig. 8.

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