UPD16686 datasheet(39/99 Pages) NEC

39 / 99 page

Data Sheet S15548EJ1V0DS

µµµµPD16686, 16687

3.6.3 Voltage regulator

The boost voltage from VOUT is supplied to the voltage regulator and output as the LCD drive voltage VLCD.

Since the

µPD16686, 16687 has a 256-step electronic volume function and an on-chip resistor for VLCD voltage regulation,

a small number of components can be used to configure a highly accurate voltage regulator.

(1) When using an on-chip resistor for VLCD voltage regulation

The on-chip resistor for VLCD voltage regulation and the electronic volume function can be used to regulate the contrast of

the LCD contents by controlling the LCD drive voltage VLCD using commands only. In such cases, no external resistor is

needed.

If VLCD

< VOUT, then the value for VLCD can be determined from the following equation.

Example Equation VLCD

< VOUT

VLCD = (1 +

Rb ) VEV

VLCD = (1 +

Rb ) (1 −

384

) VREG

Remark VEV = (1

−

384

) VREG

Figure 3-13. When Using On-Chip Resistor for VLCD Voltage Regulation

VLCD

VEV (Constant voltage source +

electronic volume)

VREG is the IC's on-chip constant voltage source, for which three types of temperature characteristic curves are available.

These temperature characteristic curves can be adjusted via settings in the power system control 1 (R32) (TSC1, TCS0),

as shown in Table 3-11.

Table 3-11 shows the VREG voltage when TA = 25

°C.

Table 3-11. VREG Voltage When TA = 25

°°°°C

Status

TCS1

TCS0

Temperature Curve

Unit

VREG (TYP.)

Unit

Internal power supply

−0.09

°C0.88

−0.11

0.80

−0.12

0.75

External inputs

−

α is the electronic volume register (R35) value. Any of 256 statuses can be set as the fetched status for α corresponding

to the data set to the 8-bit electronic control register.

α values based on settings in the electronic volume register (R35:

normal display mode) and partial electronic volume register (R36: partial display mode) are listed in Table 3-12 on the next page.

UPD16686 Datasheet(PDF) 39 Page - NEC

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