EVALED7706 STMicroelectronics, EVALED7706 Datasheet - Page 30

• Manufacturer Part Number: EVALED7706
• Description: EVALUATION BOARD FOR LED7706
• Manufacturer: STMicroelectronics

Specifications of EVALED7706

• Current - Output / Channel: 30mA
• Outputs And Type: 6, Non-Isolated
• Voltage - Output: 36 V
• Features: Dimmable, Extra 5V Output
• Voltage - Input: 4.5 ~ 36 V
• Utilized Ic / Part: LED7706
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6445

Application information
6.4
6.4.1
6.4.2
6.4.3
30/46
Design example
In order to help the design of an application using the LED7706, in this section a simple
step-by-step design example is provided.
A possible application could be the LED backlight in a 15” LCD panel using the LED7706.
Here below the possible application conditions are listed:
●
●
●
Switching frequency setting
To reduce the number of the external components, the default switching frequency is
selected (660 kHz typ.) by connecting the FSW pin to AVCC pin.
However, in case a different switching frequency is required, a resistor from FSW pin and
ground can be connected, according to the equation (5) in
Row current setting
Considering the equation 10 in
Equation 25
The closest standard commercial value is 51 kΩ. The actual value of the row current will be
a little lower (19.3 mA).
Inductor choice
The boost section, as all DC-DC converters, can work in CCM (continuous conduction
mode) or in DCM (discontinuous conduction mode) depending on load current, input and
output voltage and other parameters, among which the inductor value.
In a boost converter it is usually preferable to work in DCM.
Once the load, the input and output voltage, and the switching frequency are fixed, the
inductor value defining the boundary between DCM and CCM operation can be calculated
as:
Equation 26
where D is the duty-cycle defined as:
V
2 strings of 48 white LEDs (20 mA) each (arranged in 6 rows, 8 LEDs per row)
V
IN
F, LEDs
= 12 ± 20 %
= 3.5 V ± 200 mV
R
RILIM
Section 5.2.1
=
L
I
ROW
K
B
R
=
R
=
0
987
⋅
, the R
20
2
D
⋅
⋅
F
(
mA
1
SW
−
V
RILIM
D
=
)
2
49
resistor can be calculated as:
.
35
Section 5.1.5
k
Ω
.
LED7706