EVALED7706 STMicroelectronics, EVALED7706 Datasheet - Page 31

• 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

LED7706
6.4.4
Equation 27
whereas R
Equation 28
and
Equation 29
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 30
Considering the input voltage range, the lower L
the condition to assure the DCM operation becomes:
Equation 31
An inductor value of 6.8 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.
Output capacitor choice
The choice of the output capacitor is mainly affected by the desired output voltage ripple.
Since the voltage across the LEDs can be considered almost constant, this ripple is
transferred across the current generators, affecting their dynamic response.
The output ripple can be estimated as (neglecting the contribution of ESR of C
in case of MLCC):
0
is:
D
V
=
OUT
1
−
,
max
V
V
OUT
I
L
IN
OUT
=
<
R
8
=
L
0
⋅
=
B
V
⎧
⎨
⎩
=
(
, F
. 0
6
V
. 0
V
I
LEDs
⋅
IN
52
OUT
OUT
I
68
ROW
,
min
,
max
)
@
=
B
@
=
=
250
will be at the lower input voltage. Hence
13
+
120
V
400
Section 6.4.4
2 .
V
IN
Ω
IN
mA
μ
,
max
,
mV
H
min
=
=
=
14
9
30
6 .
4 .
V
V
V
), the rated RMS current
Application information
OUT
, very low
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