ADP5501 Analog Devices, ADP5501 Datasheet - Page 27

• Manufacturer Part Number: ADP5501
• Description: Programmable Current Backlight Driver with Ambient Light Sensor Input
• Manufacturer: Analog Devices

Specifications of ADP5501

• Vin Range: 2.7 to 5.5V
• Vout (v): 24 to 27
• Synchronous: No
• Package: 24-Lead LFCSP
• Led Configuration: Serial
• Topology: Inductive
• I2c Support: Yes
• Max Iout (ma): 30mA
• Brightness Control: I2C
• Switching Frequency: 1MHz
• Over Volt Protection (v): 24V

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.
GND
VBAT
SOLUTION SIZE
APPROXIMATELY 47mm
2
Figure 46. Example PCB Layout
Rev. 0 | Page 27 of 28
PGND
INT
SDA
SCL
NC
SW
GND
PAD TO
ADP
CONNE
EXPO
5501
SED
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
GND
CT
3.3V
2.7V TO 5.5V
CMP_IN
VDDIO
GND
LED0
LED2
GND
RST
1µF
21
16
15
1
5
4
3
Figure 45. Typical Configuration Circuit
NC
PGND
VBAT
VDDIO
SCL
SDA
INT
RST
4.7µH
6
NC
TOP OF LED STRING
BOTTOM OF LED STRIN
7
SW
NC
2
8
1µF
NC
9
BST
NC
22
10
ADP5501
NC
11
LED1
G
12
LED2
RGB
13
BL_SNK
CAP_OUT
CMP_IN
23
ADP5501
LED0
GND
GND
GND
14
20
19
18
24
17
3.3V
1µF
100nF
3.3V