Datasheet

Chapter 9 Liquid Crystal Display Driver (S08LCDV1)
MC9S08LC60 Series Data Sheet: Technical Data, Rev. 4
Freescale Semiconductor 151
Figure 9-17. LCD Charge Pump and V
LCD
Voltage Divider Block Diagram
Figure 9-17 also illustrates a buffer, a voltage follower with an ideal op amp. The buffer, if enabled, gives
VIn = VOut, and, because the input impedance of the op amp is very high, VIn is isolated from VOut This
isolation can protect VIn from things like current draw from VOut; however, if the buffer is disabled
((~BBYPASS & powersw3) = 0), the output and input will be configured in a tri-state condition; that is,
floating.
NOTE:
The charge pump is optimized for 1/3 bias mode operation only.
During the first 16 timebase clock cycles after the LCDCPEN bit is set, all
the LCD frontplane and backplane outputs are disabled regardless of state
of the LCDEN bit.
The charge pump requires external capacitance for is operation. To provide
this external capacitance, the V
cap1
and V
cap2
external pins are provided. It
is recommended that a low equivalent series resistance (ESR) capacitor be
used. Proper orientation is imperative when using a polarized capacitor. The
recommended value for the external capacitor is 0.1 μF.
V
DD
V
LL1
V
LL2
V
LL3
V
LCD
CHARGE PUMP
powersw1
powersw2
+
–
(~(BBYPASS) & powersw3)
~(LCDCPMS)
LCDCPMS
(~(LCDCPMS) & powersw3)
(BBYPASS & powersw3)
R1
R1
R1
VOLTAGE DIVIDER
BLOCK
V
LL1
VSUPPLY[1:0] powersw1 powersw2 powersw3
00 1 0 0
01 0 1 0
10 0 0 1
11 0 0 0