ADM8845 Analog Devices, ADM8845 Datasheet - Page 14

• Manufacturer Part Number: ADM8845
• Description: Charge Pump Driver for 6 White LED LCD Backlights
• Manufacturer: Analog Devices

Specifications of ADM8845

• Vin Range: 2.6 to 5.5V
• Vout (v): Vin to 5.5
• Synchronous: No
• Package: 16-Lead LFCSP
• Led Configuration: Parallel
• Topology: Capacitive
• I2c Support: No
• Max Iout (ma): 30mA
• Brightness Control: PWM
• Peak Efficiency (%): 88%
• Switching Frequency: 1.5MHz

ADM8845
APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the s switching behavior of the ADM8845, 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 I
is because the ADM8845 uses six internal currents sinks to
produce the LED current. If an LED is shorted, the ADM8845
continues to sink (I
through the shorted LED.
2.6V–5.5V
CTRL1
CTRL2
V
CC
ADM8845
GND
R
SET
2.6V–5.5V
Figure 28. Driving Five White LEDs
SET
V
FB1
FB2
FB3
FB4
FB5
FB6
OUT
V
× 120 mA) as programmed by R
CC
LED
per LED (I
CTRL1
CTRL2
I
SET
ADM8845
GND
LED
V
= I
FB1
FB2
FB3
FB4
FB5
FB6
OUT
SET
× 120 mA). This
LCD
Figure 30. Typical Application Diagram
SET
Rev. C | Page 14 of 20
MAIN DISPLAY
R
SET
2.6V–5.5V
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.
V
CC
CTRL1
CTRL2
I
SET
Figure 29. Driving Three Main LEDs and One Sub LED
ADM8845
GND
V
FB1
FB2
FB3
FB4
FB5
FB6
OUT
SUB DISPLAY
MAIN DISPLAY
SUB DISPLAY