ML9058 Datasheet, PDF (34/76 Pages) OKI electronic componets – 132-Channel LCD Driver with Built-in RAM for LCD Dot Matrix Displays

OKI Semiconductor
FEDL9058-01
ML9058
(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 V_SS & 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<V_OUT by setting the external
resistors Ra' and Rb' appropriately.
V1 = (1 + (Rb'/Ra')) • VEV = (1 + (Rb'/Ra')) • (1 – (α/324)) • VREG (Eqn. B-1)
External Rb'
VR
External Ra'
VSS
–
+
V1
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
MΩ (Eqn. B-3)
and hence,
Rb'/Ra' = 1.58, Ra' = 543 kΩ, 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
V1
Min
Typ
Max
Unit
Variable-voltage range
6.24 (α = 63)
7.0 (α = 31)
7.74 (α = 0)
[V]
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