DN66
An OLED bias supply for a clamshell handset sub display
Description
Portable applications such as cell phones are becoming increasingly complex with more and
more features designed into every generation. One popular feature is to replace the STN sub
display with an OLED sub display. OLED displays have infinite contrast ratio and are self-
illuminating. This gives the handset manufacturer two key advantages, the first is lower power
consumption and the second is a slimmer display. One disadvantage with OLED sub displays over
LCD sub displays is the higher leakage current when not in use, which is the majority of the time.
The way to overcome this issue is to disconnect the OLED sub display when the handset is
dormant.
The ZXLB1600 is a boost converter that can provide the power requirements for OLED sub display
with the additional feature of a fully integrated isolation switch which disconnects the input from
output when the ZXLB1600 is shutdown, making it ideally suited to OLED biasing.
The schematic diagram in Figure 1 shows a full color OLED bias supply for clamshell handset sub
display.
L1
U2
BAT54S
OUTPUT
U1
VBATT
V
IN
C3
SW
LX
SENSE
FB
ADJ
R1
N/C
N/C
R2
C2
C1
N/C
N/C
LBF
EN
LBT
GND
ZXLB1600
Figure 1
Schematic diagram
Note:
For applications where OLED leakage is not an issue and the ZXLB1600 isolation switch is not
needed, the SW pin can be shorted to the V
IN
pin, giving a further 3% to 5% improvement in
efficiency.
Issue 4 - July 2006
漏 Zetex Semiconductors plc 2006
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www.zetex.com
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