STEVAL-ILL021V1 STMicroelectronics, STEVAL-ILL021V1 Datasheet - Page 32

• 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
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Equation 25
where D is the duty-cycle defined as:
Equation 26
whereas R
Equation 27
and
Equation 28
The output voltage in the above calculations is considered as the maximum value (LED with
the maximum forward voltage connected to the leading generator):
Equation 29
Considering the input voltage range, the lower L
the condition to assure the DCM operation becomes:
Equation 30
An inductor value of 4.7 µH could be a suitable value, considering also a margin from the
boundary condition.
It is important to highlight that the inductor choice involves not only the value itself but the
saturation current (higher than the current limit, see
(the compliance with the saturation current might be not enough; also the thermal
performances must be taken into account), the DCR (which affects the efficiency) and the
size (in some application might be a strict requirement).
However the DCR can’t be reduced keeping the size small. Hence a trade off between these
two requirements must be achieved according to the application.
0
is:
D
V
OUT
=
1
,
−
max
V
V
OUT
I
=
IN
OUT
L
7
L
<
R
B
⋅
=
V
L
0
=
=
⎧
⎨
⎩
, F
B
=
6
. 0
. 0
LEDs
(
R
V
⋅
V
50
I
0
59
I
IN
OUT
ROW
OUT
⋅
,
min
,
2
D
max
⋅
⋅
F
@
@
)
B
(
=
=
1
SW
=
+
will be at the lower input voltage. Hence
−
74
360
700
5
D
V
6 .
Section 6.4.4
V
Ω
IN
)
IN
μ
2
mA
,
mV
,
max
min
H
=
=
=
10
26
13
8 .
6 .
2 .
V
V
V
), the rated RMS current
LED7707