ISL97702

FN7462 Rev 0.00

Page 11 of 13

October 13, 2005

Typical Application

Typical applications are passive- or active-matrix organic light

emitting diode displays (PMOLED, AMOLED) in handheld

devices. Applications with low power or screen saver/ reduced

brightness modes are also directly supported.

Motivation: In the low power mode the OLED display

brightness (~pixel current) is reduced so that the display

drivers can operate with equally reduced power. Usually the

supply voltage is kept at the same level, although the pixel

voltage drops by several volts when the pixel current levels are

reduced. Here a further power reduction can be achieved if the

supply voltage for the display drivers is reduced according to

the pixel diode characteristic.

The ISL97702 allows selection between a nominal and a

reduced output voltage level in order to supply more effectively

OLED display drivers.

Components Selection

The input capacitance is normally 10µf~15µF and the output

capacitor is 3.3µf to 6.6µF. X5R or X7R type of ceramic

capacitor with correct voltage rating is recommended. The

output capacitor value will affect the output voltage ripple.

Higher value of the output capacitor, lower ripple of the output

voltage.

When choosing an inductor, make sure the inductor can

handle the average and peak currents given by following

formulas (80% efficiency assumed):

Where:

•

• L inductance in H

Optimal combination of the boost inductor L and the output

capacitor Cout are listed in table:

Recommended Inductor and Ceramic capacitor manufactures

are listed in the following table:

PCB layout Considerations

The layout is very important for the converter to function

properly. To ensure the high pulse current in the power ground

does not interfere with the sensitive feedback signals, the

should be as short as possible. For the DFN package, there is

FIGURE 20. ISL97702 APPLICATION BOARD

GND

1

VDDOUT

2

VDD

3

NSYNC

4

FB0

5

FB1

6

SEL

7

NEN

8

VOUT

9

LX 10

U1

L1

6.8µH

C1

100n

C2

10µ

J1

VDD_IN

J2

GND_IN

J3

GND_OUT

J4

NSYNC

J5

J6

J7

VOUT

R1

390K

R2

OPEN

R3

OPEN

R4

OPEN

R5

26.1K

R6

39K

C3

OPEN

C4

OPEN

C5

OPEN

C8

100n

2

J1

2

J2

VDD

VDD

VDD

JP3

VDD

C6

1nF/50V

C7

3.3µF/50V

C9

4.7µ/10V

ISL97702

SEL

NEN





----------------------------------

=

(EQ. 1)

1

2

---

+



=

(EQ. 2)

INDUCTOR (µH)

CAPACITOR (µF)

MIN

MAX

4.7

2.2

10

6.8

3.3

10

10

4.7

10

15

6.8

10

INDUCTOR

CERAMIC CAPACITOR

Sumida: www.sumida.com

Taiyo Yuden: www.t-yuden.com

TDK:

www.tdk.co.jp

AVX:

www.avxcorp.com

Toko:

www.tokoam.com

Murata:

www.murata.com

–







---------------------------------------------------

=

(EQ. 3)