STEVAL-ILL021V1 STMicroelectronics, STEVAL-ILL021V1 Datasheet - Page 30

• Manufacturer Part Number: STEVAL-ILL021V1
• Description: BOARD EVAL LCD BACKLIGHT LED7707
• Manufacturer: STMicroelectronics

Specifications of STEVAL-ILL021V1

• Design Resources: STEVAL-ILL021V1 Bill of Material STEVAL-ILL021V1 Schematic
• Current - Output / Channel: 85mA
• Outputs And Type: 6, Non-Isolated
• Voltage - Output: 36 V
• Features: Dimmable, Extra 5V Output
• Voltage - Input: 4.5 ~ 36 V
• Utilized Ic / Part: LED7707
• Description/function: LCD backlight demonstration board
• Operating Voltage: 4.5 V to 36 V
• Product: Display Modules
• Core Chip: LED7707
• No. Of Outputs: 1
• Output Voltage: 36V
• Dimming Control Type: PWM
• Mcu Supported Families: LED7707
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption
• For Use With/related Products: LED7707
• Other names: 497-10044

Application information
6.3
6.3.1
6.3.2
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Component selection
Inductor selection
Being the LED7707 mostly dedicated to backlighting, real-estate applications dictate severe
constrain in selecting the optimal inductor. The inductor choice must take into account
different parameters like conduction losses (DCR), core losses (ferrite or iron-powder),
saturation current and magnetic-flux shielding (core shape and technology).
The switching frequency of the LED7707 can be set in the 200 kHz-1 MHz range, allowing a
wide selecting room for the inductance value. Low switching frequencies takes to high
inductance value, resulting in significant DCR and size. On the other hand, high switching
frequencies result in significant core losses. The suggested range is 4.7-22 µH, even if the
best trade off between the different loss contributions varies from manufacturer to
manufacturer.
A 6.8 µH inductor has been experimentally found as the most suitable for applications
running at a 660 kHz switching frequency.
Table 7.
Capacitors selection
The input and output capacitors should have very low ESR (ceramic capacitors) in order to
minimize the ripple voltage. The boost converter of the LED7707 has been designed to
support ceramic capacitors. The required capacitance depends on the programmed LED
current and the minimum dimming frequency (the boost converter is off when the DIM pin is
low and the output capacitor is slowly discharged). Considering the worst case (i.e. 200 Hz
dimming frequency and 85 mA/channel), two 4.4 µF MLCCs are suitable for almost all
applications. Particular care must be taken when selecting the rated voltage and the
dielectric type of the output capacitors: 50 V rated MLCC may show a significant
capacitance drop when biased, especially in case of Y5V dielectric.
As in most of boost converters, the input capacitor is less critical, although it is necessary to
reduce the switching noise on the supply rail. The input capacitor is also important for the
internal LDO of the LED7707 and must be kept as close as possible to the chip. The rated
voltage of the input capacitor can be chosen according to the supply voltage range; a 10 µF
X5R MLCC is recommended.
Table 8.
Manufacturer
Taiyo Yuden
Manufacturer
Murata
Coilcraft
Coilcraft
Wurth
Recommended inductors
Recommended capacitors
GRM31CR71H225KA88B
UMK325BJ106KM-T
Part number
LPS6235-682MLC
XPL7030-682ML
Part number
7440650068
Ceramic, 35V, X5R, 20 %
Ceramic, 50V, X7R, 20 %
6.8 μH, 75 mΩ, 2.7 A
6.8 μH, 60 mΩ, 5.8 A
6.8 μH, 33 mΩ, 3.6 A
Description
Description
SMD 1210
SMD 1206
Package
10x10 mm
6x6 mm
7x7 mm
Size
LED7707
Notes
C
C
OUT
IN