ADP5501 datasheet(27/28 Pages) AD

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ADP5501

Rev. 0 | Page 27 of 28

Component Selection

The ADP5501 boost converter is designed for use with a 4.7 μH

inductor. Choose an inductor with a sufficient current rating to

prevent it from going into saturation. The peak current limit of

the ADP5501 is 750 mA (maximum), so choose an inductor

with a greater saturation rating. To maximize efficiency, choose

an inductor with a low series resistance (DCR).

The ADP5501 is an asynchronous boost and, as such, requires

an external Schottky diode to conduct the inductor current to

the output capacitor and LED string when the power switch is

off. Ensure that the Schottky diode peak current rating is greater

than the maximum inductor current. Choose a Schottky diode

with an average current rating that is significantly larger than

the maximum LED current. To prevent thermal runaway, derate

the Schottky diode to ensure reliable operation at high junction

temperatures. To maximize efficiency, select a Schottky diode

with a low forward voltage. When the power switch is on, the

Schottky diode blocks the dc path from the output capacitor to

ground. Therefore, choose a Schottky diode with a reverse

breakdown greater than the maximum boost voltage. A 40 V,

1 A Schottky diode is recommended.

The input capacitor carries the input ripple current, allowing

the input power source to supply only the dc current. Use an

input capacitor with sufficient ripple current rating to handle

the inductor ripple. A 1 μF X5R/X7R ceramic capacitor rated

for 16 V dc bias is recommended for the input capacitance.

The output capacitor maintains the output voltage when the

Schottky diode is not conducting. Due to the high levels of

boost voltage required, a 1 μF X5R/X7R ceramic capacitor rated

for 50 V dc bias is recommended for output capacitance.

Note that dc bias characterization data is available from

capacitor manufacturers and should be taken into account

when selecting input and output capacitors.

PCB LAYOUT

Good PCB layout is important to maximize efficiency and to

minimize noise and electromagnetic interference (EMI). To

minimize large current loops, place the input capacitor, inductor,

Schottky diode, and output capacitor as close as possible to each

other and to the ADP5501 using wide tracks (use shapes where

possible).

For thermal relief, the exposed pad of the LFCSP package

should be connected to ground (GND). PGND and GND

should be connected to each other at the bottom of the output

capacitor.

Figure 46 shows an example PCB layout with the main power

components required for backlight driving

EXAMPLE CIRCUIT

PGND

VBAT

1µF

2.7V TO 5.5V

1µF

4.7µH

VDDIO

SCL

SDA

INT

RST

ADP5501

3.3V

BST

BL_SNK

CAP_OUT

LED2

LED1

LED0

3.3V

1µF

GND

3.3V

100nF

CMP_IN

RGB

Figure 45. Typical Configuration Circuit

GND

VBAT

GND

CMP_IN

PGND

INT

SDA

SCL

ADP

VDDIO

RST

LED0

LED2

5501

CONNE

EXPO

PAD TO

TOP OF LED STRING

BOTTOM OF LED STRIN

SED

GND

SOLUTION SIZE

APPROXIMATELY 47mm2

Figure 46. Example PCB Layout

ADP5501 Datasheet(PDF) 27 Page - Analog Devices

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