STEVAL-ILL021V1 STMicroelectronics, STEVAL-ILL021V1 Datasheet - Page 34

• 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
6.4.5
34/47
T
Equation 35
defining D
Equation 36
The worst case for the output voltage ripple is when input voltage is lower (V
A simple way to select the C
In order to affect as less as possible the current generators, it would be better to fix the
maximum ripple lower than the typical voltage across the generators.
For example considering ΔV
leading generator), the required capacitance is:
Equation 37
A margin from the calculated value should be taken into account because of the
capacitance drop due to the applied voltage when MLCCs are used.
One 10 µF MLCC (or two 4.7 µF MLCCs) can be a good choice for this application.
In case a dimming duty cycle different from 100% is used, a further contribution to the
capacitor discharge (during the off time of the dimming cycle) should be considered.
Input capacitor choice
The input capacitor of a boost converter is less critical than the output capacitor, due to the
fact that the inductor is in series with the input, and hence, the input current waveform is
continuous.
A low ESR capacitor is always recommended.
A capacitor of 10 µF is tentatively a good choice for most of the applications.
OFF
can be calculated as:
2
as:
D
T
2
OFF
=
=
C
2
OUT
OUT
R
T
OUT
⋅
SW
F
0
SW
⋅
lower than 70 mV (i.e. the 10 % of the voltage across the
value is fixing a maximum voltage ripple.
(
⋅
M
>
D
⋅
L
(
−
2
I
, L
⋅
1
=
peak
M
)
2
⎧
⎨
⎩
Δ ⋅
618
569
=
−
⎧
⎨
⎩
V
I
. 0
. 0
OUT
OUT
2 .
7 .
408
376
ns
ns
,
max
)
⋅
T
@
@
OFF
@
@
V
=
V
V
V
IN
IN
. 6
IN
IN
,
,
max
min
,
,
33
max
min
μ
=
=
=
F
=
10
13
10
13
8 .
2 .
8 .
2 .
V
V
V
V
IN,min
= 10.8 V).
LED7707