Datasheet

Chapter 9 Liquid Crystal Display Driver (S08LCDV1)
MC9S08LC60 Series Data Sheet: Technical Data, Rev. 4
154 Freescale Semiconductor
The output of the voltage divider block is V
LL1.
V
LL1
is connected to the internal charge pump via the V
ref.
Using the charge pump, the value of V
LL1
is tripled and outputted as V
LL3.
V
LL3
, a LCD bias voltage, is
equal to the voltage required to energize the LCD panel, V
LCDON.
For 3-V LCD glass, V
LL3
should be
approximately 3-V; while for 5-V LCD glass, V
LL3
should be approximately 5-V.
Depending on the LCDCPMS bit configuration, V
LL3
will be equal to 3*V
LCD
or 3*(2/3*V
LCD
) (see
Section 9.4.4, “LCD Charge Pump, Voltage Divider, and Power Supply Operation). Table 9-19 shows the
selected V
LL1
and V
LL3
values based on the input value of V
LCD
.
In addition to V
LL1
and V
LL3
, V
LL2
is also generated internally when the charge pump is enabled
(LCDCPEN = 1). For a typical LCD panel, the bias voltages in 1/3 bias mode would be:
•V
3
= V
LL3
= V
LCDON
=3× V
ref
•V
2
= V
LL2
= 2 × V
ref
•V
1
= V
LL1
= V
ref
•V
0
= V
SS
NOTE
V
LCDON
is the LCD panel driving voltage required to turn on an LCD
segment. Since V
LL3
and V
LCDON
are equivalent, V
LL3
should be
configured so that it is 3 V or 5 V, depending on the LCD panel specification.
9.4.4.2.2 LCD External Power Supply, VSPUPPLY[1:0] = 11
When VSPUPPLY[1:0] = 11, powersw1, powersw2, and powersw3 are deasserted. Moreover with
powersw3 deasserted, the buffer is disabled ((~BBYPASS & pwersw3) = 0), so V
LCD
will be configured
in a tri-state condition. V
DD
is not available to power the LCD module internally, so the LCD module
requires an external power source for V
LL1,
V
LL2,
and V
LL3
when the charge pump is disabled. If the
charge pump is enabled, external power must be applied to either V
LL1,
V
LL2,
or V
LL3
.
9.4.4.2.3 LCD Internal Power Supply, VSUPPLY[1:0] = 00 or 01
V
DD
is specified to be from 1.8 V to 3.6 V. V
DD
is used as the LCD module power supply when
VSUPPLY[1:0] = 00 or 01(see Table 9-18). When powering the LCD module using V
DD
, the charge pump
must be enabled (LCDCPEN = 1). Table 9-20 provides recommendations regarding configuration of the
VSUPPLY[1:0] bit field when using both 3-V and 5-V LCD panels.
Table 9-19. V
LL1
Typical Values
V
LCD
LCDCPMS = 0
Voltage Doubler
LCDCPMS = 1
Voltage Tripler
V
LL1
= V
ref
V
LL3
= 3 × V
ref
V
LL1
= V
ref
V
LL3
= 3 × V
ref
1.4 V (2/3) × 1.4 V 2.8 V 1.4 V 4.2 V
1.5 V (2/3) × 1.5 V 3.0 V 1.5 V 4.5 V
1.7 V (2/3) × 1.7 V 3.3 V 1.67 V 5.0 V
1.8 V (2/3) × 1.8 V 3.6 V 1.8 V 5.4 V