LED7706 STMicroelectronics, LED7706 Datasheet - Page 27

• 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
6.2
Thermal considerations
In order to prevent the device from exceeding the thermal shutdown threshold (150 °C), it is
important to estimate the junction temperature through the following equation:
Equation 18
where T
ambient and P
The R
is 42 °C/W.
The P
Equation 19
where D is defined as:
Equation 20
and D
Equation 21
where t
Equation 22
where I
master current generator (typically 400 mV).
The voltages across the other current generators depend on the spread of the LEDs forward
voltage. The worst case for power dissipation (maximum forward voltage LEDs in the master
row, minimum forward voltage LEDs in all other rows) can be estimated as:
a)
b)
c)
D,tot
DIM
th,JA
r
ROW
A
and t
Conduction losses due to the R
Switching losses due to the power MOSFET turn on and off, calculated as:
Current generators losses. This contribution is strictly related to the LEDs used in
the application. Only the contribution of the leading current generator (“master”
current generator) can be predicted, regardless of the LEDs forward voltage:
is the ambient temperature, R
is the duty cycle of the PWM dimming signal.
has several contributions, listed below.
measured on the application demonstration board (described in
is the current flowing through the row, whereas V
f
D,tot
are the power MOSFET rise time and fall time respectively.
is the power dissipated by the device.
P
, D
sw
P
P
GEN
, D
T
=
cond
J
V
,
Master
=
OUT
T
D
=
th,JA
Amb
DS(on)
R
⋅
=
I
=
DSon
IN
1
I
+
is the equivalent thermal resistance junction to
−
ROW
⋅
R
f
sw
V
of the internal power switch, equal to:\
⋅
th
V
OUT
I
IN
,
2
IN
⋅
⋅
JA
t (
V
⋅
r
IFB
D
⋅
P
+
2
⋅
, D
D
⋅
) t
D
f
tot
DIM
DIM
⋅
D
DIM
IFB
is the voltage across the
Application information
Section 6.5
)
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