ADM8845 datasheet(14/20 Pages) AD

14 / 20 page

ADM8845

Rev. 0 | Page 14 of 20

APPLICATIONS

LAYOUT CONSIDERATIONS AND NOISE

Because of the ADM8845’s switching behavior, PCB trace layout

is an important consideration. To ensure optimum performance,

a ground plane should be used, and all capacitors (C1, C2, C3,

C4) must be located with minimal track lengths to the pins of

the ADM8845.

WHITE LED SHORTING

If an LED is shorted, the ADM8845 continues to drive the

remaining LEDs with ILED per LED (ILED = ISET × 120 mA). This

is because the ADM8845 uses six internal currents sinks to

produce the LED current. If an LED is shorted, the ADM8845

continues to sink (ISET × 120 mA) as programmed by RSET

through the shorted LED.

DRIVING FEWER THAN SIX LEDS

The ADM8845 can be operated with fewer than six LEDs in

parallel by simply leaving the unused FBx pins floating or

connected to GND. For example, Figure 28 shows five LEDs

being powered by the ADM8845, and Figure 29 shows three

main LEDs and one sub LED.

VOUT

FB1

FB2

FB3

FB4

FB5

FB6

VCC

2.6V–5.5V

CTRL1

CTRL2

GND

ADM8845

LCD

Figure 28. Driving Five White LEDs

VOUT

FB1

FB2

FB3

FB4

FB5

FB6

VCC

2.6V–5.5V

CTRL1

CTRL2

GND

ADM8845

RSET

ISET

MAIN DISPLAY

SUB DISPLAY

Figure 29. Driving Three Main LEDs and One Sub LED

VOUT

FB1

FB2

FB3

FB4

FB5

FB6

VCC

2.6V–5.5V

CTRL1

CTRL2

GND

ADM8845

RSET

ISET

MAIN DISPLAY

SUB DISPLAY

Figure 30. Typical Application Diagram

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