LED7706 STMicroelectronics, LED7706 Datasheet - Page 33

• Manufacturer Part Number: LED7706
• Description: IC LED DRIVR WHT BCKLT 24-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Backlight, White LEDr

Specifications of LED7706

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 250kHz ~ 1MHz
• Voltage - Supply: 4.5 V ~ 36 V
• Voltage - Output: 36V
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Operating Supply Voltage: 4.5 V to 36 V
• Maximum Supply Current: 1 mA
• Maximum Power Dissipation: 2300 mW
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• For Use With: 497-10043 - BOARD EVAL LCD BACKLIGHT LED7706497-8360 - BOARD EVAL FOR LED7707497-6445 - EVALUATION BOARD FOR LED7706
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Operating Temperature: -
• Efficiency: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

LED7706
6.4.5
6.4.6
Equation 37
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 38
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.
A 4.7 µF MLCC can be a good choice for this application (two 2.2 μF MLCC in parallel can
be also a good solution).
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.
Over-voltage protection divider setting
The over-voltage protection (OVP) divider provides a partition of the output voltage to the
OVSEL pin. The OVP divider setting not only fixes the OVP threshold, but also the open-
channel detection threshold (95 % of the OVP threshold).
The proper OVP divider setting can be calculated by the equation (3):
Equation 39
where V
the maximum V
OUT, MAX
F
is the maximum output voltage considering the worst case (all LEDs with
= V
D
F,max
2
=
= 3.7 V on the same row):
C
2
OUT
OUT
R
R
OUT
⋅
F
0
2
SW
⋅
=
lower than 80 mV (i.e. the 20 % of the voltage across the
value is fixing a maximum voltage ripple.
(
M
>
R
⋅
L
(
−
1
I
, L
⋅
⋅
1
peak
M
V (
)
2
OUT
Δ ⋅
=
−
⎧
⎨
⎩
V
,
I
. 0
MAX
OUT
OUT
. 0
263
. 1
23
,
max
)
+
234
⋅
T
2
OFF
V
@
@
V
−
. 1
=
V
V
234
. 2
IN
IN
,
,
02
max
min
) V
μ
F
=
=
9
14
6 .
Application information
4 .
V
V
IN,min
= 9.6 V).
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