LED7706 STMicroelectronics, LED7706 Datasheet - Page 28

• 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

Application information
6.3
6.3.1
28/46
Equation 23
where n
voltage and n
Equation 24
The LED7706 is housed in a 24 leads 4x4-VFQFPN package with exposed pad that allows
good thermal performance. However it is also important to design properly the
demonstration board layout in order to assure correct heat dissipation.
Figure 19
infrared camera. The chip temperature, in those application conditions, is kept below 50 °C.
Figure 19. Demonstration board thermographic analysis
Component selection
Inductor selection
Being the LED7706 mostly dedicated to backlighting, real-estate applications dictate severe
constrain in selecting the optimal inductor. The inductor choice must take into account
different parameters like conduction losses (DCR), core losses (ferrite or iron-powder),
saturation current and magnetic-flux shielding (core shape and technology).
The switching frequency of the LED7706 can be set in the 200 kHz-1 MHz range, allowing a
wide selecting room for the inductance value. Low switching frequencies takes to high
inductance value, resulting in significant DCR and size. On the other hand, high switching
frequencies result in significant core losses. The suggested range is 4.7-22 µH, even if the
d)
V
V
I
I
V
V
F
F
D
D
T
T
ROWs
ROW
ROW
SW
SW
IN
IN
OUT
OUT
Amb
Amb
DIM
DIM
LDO losses, due to the dissipation of the 5 V linear regulator:
shows a picture of the LED7706 application demonstration board taken using an
= 12V
= 12V
= 660kHz
= 660kHz
= 90%
= 90%
= 30°C
= 30°C
= 20mA
= 20mA
LEDs
= 34V
= 34V
is the number of active rows, Δ V
is the number of LEDs per row.
P
GEN
=
I
ROW
⋅
(
P
n
, D
ROWs
LDO
−
=
1
(
)
V
⋅
IN
(
V
IFB
−
f,LEDs
V
LDO
+
Δ
is the spread of the LEDs forward
V
)
⋅
, f
I
LEDs
LDO
⋅
n
LEDs
)
⋅
D
DIM
LED7706