Issue 4 - July 2006

1

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© Zetex Semiconductors plc 2006

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.

Figure 1

Schematic diagram

Note:

For applications where OLED leakage is not an issue and the ZXLB1600 isolation switch is not

efficiency.

SW

V

IN

LBF

EN

LBT

GND

ADJ

FB

SENSE

LX

U1

ZXLB1600

L1

C2

OUTPUT

C1

VBATT

U2

BAT54S

R1

R2

N/C

N/C

N/C

N/C

C3