LED7707 STMicroelectronics, LED7707 Datasheet - Page 28

• Manufacturer Part Number: LED7707
• Description: LED Drivers 6-ROW 85mA LED DRIV BOOST REG LCD PANEL
• Manufacturer: STMicroelectronics

Specifications of LED7707

• High Level Output Current: 85 mA
• Operating Supply Voltage: 4.5 V to 36 V
• Maximum Supply Current: 1 mA
• Maximum Power Dissipation: 2.3 W
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Package / Case: VFQFPN-24
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
6.2
28/47
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 17
where T
ambient and P
The R
42 °C/W.
The P
Equation 18
where D is defined as:
Equation 19
and D
Equation 20
where t
Equation 21
where I
master current generator (typically 700 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
D
T
=
th,JA
A
DS(on)
R
⋅
=
I
=
DSon
IN
+
1
I
is the equivalent thermal resistance junction to
R
−
ROW
⋅
f
sw
V
th
of the internal power switch, equal to:
⋅
V
OUT
,
I
JA
IN
2
IN
⋅
⋅
t (
V
⋅
⋅
r
IFB
D
P
+
2
D
⋅
D
⋅
) t
,
D
tot
f
DIM
DIM
⋅
D
DIM
IFB
is the voltage across the
Section 6.5
LED7707
) is