CL-PS7110-VC-A View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CL-PS7110-VC-A' PDF : 82 Pages View PDF
CL-PS7110
Low-Power System-on-a-Chip
to 15-in-16. The sense of the DC-to-DC converter drive signal (active-high or -low) is determined by latch-
ing the state of this drive signal during power-on reset (that is, a pull-up resistor on the drive signal results
in an active-low drive output and vice versa). This allows either positive or negative voltages to be gener-
ated by the DC-to-DC converter.
An example of how to use the DC-to-DC converter is shown below. The objective of Example 1 is to have
constant VEE for the bias generator of an LCD panel to control the contrast. Four of the GPIO pins (shown
as PD4, PD5, PD6 and PD7 in Figure 1-2 and Figure 1-3) are used to choose various resistor values. The
Drive 1 pin is connected to the base of the biasing transistor. The VEE is the maximum voltage that is
required.The feedback mechanism via the FB1 pin ensures that whenever software changes the pulse
width using the Pump Control register (PMPCON), the voltage level is kept at the desired level for VEE.
The same technique could be used for keeping VPP for flash at a constant level as shown in Example 2.
Example 1
Following is a sample schematic for a positive and negative VEE control circuitry. The same circuitry may
be applied for the 12-V VPP generator. Assume that the nominal VEE voltage for a given LCD is 28 V, and
the range covered is from 27 to 29 V (to assure a sufficient contrast control range).
Resistor
R75
R53
R54
R55
R62–65
Notes
Pull down for positive VEE.
Pull up for LM339 open-drain output.
Choose to select a voltage at the + terminal of the com-
parator at what point the feedback output will switch off
(high), thus turning off the Drive output.
To select voltage level on the + input of the comparator to
application VREF (1.5V).
This resistor network allows VEE to be programmed
under program control. If all outputs are low, VEE is at the
maximum. Turning on the outputs increases the voltage
at the comparator, and therefore decreases VEE.
1. Connect a load resistor over C2 to force approximately 2 mA of current (or whatever your panel’s typical
value is).
2. Program the Pump Control register to 5, set PD7..4 to high.
3. Set R55 such that VEE is at the minimum 27 V.
4. Set PC7..4 to ‘1111’; VEE should exceed 29 V.
24
FUNCTIONAL DESCRIPTION
May 1997
DATA BOOK v1.5
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