LED7707 STMicroelectronics, LED7707 Datasheet - Page 36

• 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
6.4.9
36/47
Power dissipation estimate
As explained in section 5.2, there are several contributions to the total power dissipation.
Neglecting the power dissipated by the LDO (surely less significant compared with the other
contributions), equation (18), (20), (21) and (22) help to estimate the overall power
dissipation.
Before starting the power dissipation estimate it is important to highlight that the following
calculations are considering the worst case (the actual value of the dissipated power would
require measurements). Therefore the power dissipation is estimated according to the
following assumptions:
1.
2.
3.
4.
The conduction and switching losses on the internal power switch can be calculated as:
Equation 41
Equation 42
where t
The power dissipation related to the current generators is given by:
Equation 43
Equation 44
Equation 45
The junction temperature can be estimated by equation (18) considering T
Equation 46
Minimum input voltage (10.8 V), which leads to maximum input current (and also D will
have the higher value, see
Maximum R
LEDs in the row of the leading generator will have the maximum forward voltage,
whereas all other LEDs in the other rows will have the minimum forward voltage.
100 % dimming signal duty cycle is considered.
r
= t
f
= 15 ns
P
GEN
DS(on)
=
P
I
ROW
, D
P
of the internal power MOSFET;
tot
, D
sw
⋅
≅
P
P
(
n
, D
GEN
P
=
ROWs
, D
cond
T
V
cond
,
J
Section 6.4.4
Master
OUT
=
=
−
T
+
R
⋅
1
Amb
I
P
)
IN
DSon
=
⋅
, D
(
I
⋅
V
sw
ROW
+
f
sw
IFB
R
⋅
+
I
IN
2
⋅
th
P
+
⋅
t (
);
,
GEN
⋅
V
JA
Δ
r
D
IFB
V
+
2
⋅
⋅
, f
,
P
Master
D
) t
LEDs
⋅
, D
f
D
DIM
tot
⋅
DIM
D
⋅
=
=
DIM
+
n
=
LEDs
72
P
216
GEN
42
=
°
C
mW
233
mW
)
⋅
=
D
. 1
DIM
mW
12
=
W
630
mW
A
= 25 °C:
LED7707