UPD16498 Datasheet, PDF (33/95 Pages) NEC – 1/128 DUTY LCD CONTROLLER/DRIVER WITH FOUR-LEVEL GRAY SCALE, ON-CHIP RAM

µPD16498
5.6.2 Voltage regulator
The boost voltage from VOUT is supplied to the voltage regulator and output as the LCD drive voltage VLCD.
Since the µPD16498 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
Ra
VLCD = (1 + ^Rb ) (1 − ^α ) VREG
Ra
384
Remark VEV = (1 − ^α ) VREG
384
Figure 5-13. When Using On-Chip Resistor for VLCD Voltage Regulation
VEV (Constant voltage source +
electronic volume)
+
-
Rb
VLCD
Ra
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 register 1 (R32) (TSC1,
TCS0), as shown in Table 5-11.
Table 5-11 shows the VREG voltage when TA = 25°C.
Table 5-11. VREG Voltage When TA = 25°C
Status
Internal power supply
TCS1
0
0
1
1
TCS0
0
1
0
1
Temperature Curve (%/°C)
−0.06
−0.08
−0.09
−0.12
VREG (TYP.) (V)
1.04
0.98
0.93
0.85
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 the partial electronic volume register (R36: partial display mode) are listed in Table 5-12.
Data Sheet S15730EJ2V0DS
33