HT45R2K-C Datasheet, PDF (80/105 Pages) Holtek Semiconductor Inc – Dual Slope 16K/8K/4K ASSP MCU for Body Fat Scale

HT45R2K-C/-B/-A
Dual Slope 16K/8K/4K ASSP MCU for Body Fat Scale
for the pixel to be on and less than the threshold voltage for the pixel to be off. The requirement
to limit the DC voltage to zero and to control as many pixels as possible with a minimum number
of connections, requires that both a time and amplitude signal is generated and applied to the
application LCD. These time and amplitude varying signals are automatically generated by the LCD
driver circuits in the microcontroller. What is known as the duty determines the number of common
lines used, which are also known as backplanes or COMs. The duty, which is chosen by control bits
to have a value of 1/4, 1/5, 1/6 or 1/7, 1/8 and which equates to a COM number of 3, 4, 5, 6 and
7 respectively, therefore defines the number of time divisions within each LCD signal frame. The
accompanying timing diagrams depict the LCD signals generated by the microcontroller for various
values of duty and bias.
LCD Voltage Source and 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 CSSn bits in the LCDC register. The device can have either R type or C type
biasing selected via the RCS bit in the LCDC register. Selecting the C type biasing will enable an
internal charge pump whose multiplying ration can be selected using an additional configuration
option.
For R type biasing an external LCD voltage source is supplied by the internal VLCD biasing
voltage. This could be the microcontroller power supply or some other voltage source. For the
R type 1/3 bias selection, three voltage levels VSS, VA, VB and VC are utilised. The voltage VA
is equal to VLCD. VB is equal to 2/3×VLCD. VC is equal to 1/3×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 also is supplied by the internal VLCD biasing
voltage or VMAX. The C type biasing scheme uses an internal charge pump circuit, which in the
case of the 1/3 bias can generate voltages higher than what is supplied by VLCD. This feature
is useful in applications where the microcontroller supply voltage is less than the supply voltage
required by the LCD.
The bit “VAS” is selected for VA voltage in C type LCD. The relation of LCD voltage is as
following figure.
V A =V LC D
V B = 2 /3 x V L C D
R
V C = 1 /3 x V L C D
R
R
VM AX=VO C H P
C1
V LC D =V O R E G
VA
VB
C2
VAB
C h a rg e
P um p
VC
VC
0 .1 m F
0 .1 m F
0 .1 m F
VM AX=VO C H P
C1
V LC D =V O R E G
C2
VAB
C h a rg e
VA
P um p
VB
VC
VC
0 .1 m F
0 .1 m F
0 .1 m F
R ty p e a n d 1 /3 B ia s
C ty p e a n d 1 /3 B ia s ,V A S = " 1 "
V A B = 3 /2 x V O R E G = V A
VB=VO R EG
V C = 1 /2 x V O R E G
Note: 1. 1/3bias, VAS= 1, → VAB is VA.
2. 1/3bias, VAS= 0, → VAB is VB.
Rev. 1.20
80
C ty p e a n d 1 /3 B ia s ,V A S = " 0 "
V A B = 3 /2 x V O R E G = V B
VA=VO R EG
V C = 1 /3 x V O R E G
May 30, 2013