Lcd Voltage Sou - Holtek TinyPower HT69F40A Manual

TinyPower
LCD Voltage Source Biasing
The time and amplitude varying signals generated by the LCD Driver function require the generation
of several voltage levels for their operation. The number of voltage levels used by the signal depends
upon the value of the BIAS bit in the LCDC register. The device can have either R type or C type
biasing selected via a configuration option. Selecting the C type biasing will enable an internal
charge pump whose multiplier ratio can be selected using an additional configuration option.
For R type biasing an external LCD voltage source must be supplied on pin VLCD to generate the
internal biasing voltages. This could be the microcontroller power supply or some other voltage
source. For the R type 1/2 bias selection, three voltage levels V
voltage V is equal to the externally supplied voltage source applied to pin VLCD. The voltage V
A
generated internally by the microcontroller and will have a value equal to V
bias selection, four voltage levels V
voltage V is equal to V
B
or 1/3 bias, several values of bias resistor can be chosen using bits in the LCDC register.
Different values of internal bias resistors can be selected using the RSEL0 and RESEL1 bits in
the LCDC register. This along with the voltage on pin VLCD will determine the bias current. The
connection to the VMAX pin depends upon the voltage that is applied to the VLCD pin. If the VDD
voltage is greater than the voltage applied to the VLCD pin then the VMAX pin should be connected
to VDD, otherwise the VMAX pin should be connected to pin VLCD. Note that no external
capacitors or resistors are required to be connected if R type biasing is used.
For C type biasing an external LCD voltage source must also be supplied on pin VLCD to generate
the internal biasing voltages. The C type biasing scheme uses an internal charge pump circuit, which
in the case of the 1/3 bias selection, can generate voltages higher than what is supplied on VLCD.
This feature is useful in applications where the microcontroller supply voltage is less than the supply
voltage required by the LCD. An additional charge pump capacitor must also be connected between
pins C1 and C2 to generate the necessary voltage levels.
For the C type 1/2 bias selection, three voltage levels V
generated internally and has a value of V
the C type 1/2 bias configuration V
For the C type 1/3 bias selection, four voltage levels V
V is generated internally and has a value of V
A
V ×2/3 and V will have a value equal to V
A C
the bias and the voltage that is applied to VLCD. It is extremely important to ensure that these
charge pump generated internal voltages do not exceed the maximum V
Rev. 1.20
HT69F30A/HT69F40A/HT69F50A
I/O Flash 8-Bit MCU with LCD & EEPROM
TM
, V , V and V
SS A B C
×2/3 while the voltage V
LCD C
Condition VMAX connection
V > V Conne�t VMAX to VDD
DD LCD
�the�wise Conne�t VMAX to VLCD
R Type Bias VMAX Pin Connection
. The voltage V
LCD
is not used.
C
×3/2. The voltage V
LCD
×1/3. The connection to the VMAX pin depends upon
A
Biasing Type
V >V ×1.�
DD LCD
1/3 Bias
�the�wise
V >V
DD LCD
1/2 Bias
�the�wise
C Type Bias VMAX Pin Connection
176
, V and V are utilised. The
SS A B
/2. For the R type 1/3
LCD
are utilised. The voltage V is equal to V
A
is equal to V ×1/3. In addition to selecting 1/2
LCD
, V and V are utilised. The voltage V
SS A B
will have a value equal to V
B
, V , V and V are utilised. The voltage
SS A B C
will have a value equal to
B
voltage of 5.5V.
DD
VMAX Connection
Conne�t VMAX to VDD
Conne�t VMAX to V1
Conne�t VMAX to VDD
Conne�t VMAX to VLCD
��to�e� 0�� 201�
is
B
. The
LCD
is
A
×1/2. For
A