AAT1407 Advanced Analogic Technologies, Inc., AAT1407 Datasheet - Page 12

• Manufacturer Part Number: AAT1407
• Description: 6 Channel Led Backlight Driver With Integrated Boost And High Frequency Direct Pwm Dimming
• Manufacturer: Advanced Analogic Technologies, Inc.

For example, if the number of white LEDs in each string
is N =11, the resistor divider R3 can be calculated by
selecting R4 = 12.1kΩ:
choose R3 = 442kΩ.
The maximum output voltage with the selected values of
R4, R3 is
LED Current Sink Setting
The current sink is controlled by the RSET voltage (0.6V)
and the R
tolerance resistor is recommended.
The R
Where V
For example, if the maximum current for each string
LEDs is 30mA, this corresponds to a minimum resistor
value of 5.23kΩ.
12
SwitchReg
V
OUT(MAX)
R
Maximum I
3
SET
> 12.1kΩ ·
Table 2: Maximum LED Current Sink vs.
= V
RSET
resistor (R2) value can be calculated as follows:
SET
TM
OVP(MAX)
= 0.6V.
resistor (R2). For maximum accuracy, a 1%
R
6 Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming
R
SET
LED
2
·
0.5V + 11 · 3.7V - 1.1
=
30
25
20
15
10
Resistor (R2) Values.
5
Current (mA)
R
R
R
262 · 0.6V
3
4
2
30mA
=
+ 1
262 · 0.6V
1.1
I
CSX(MAX)
=
1.3V ·
= 5.23kΩ
12.1kΩ
442kΩ
= 441.1kΩ
R2 (kΩ)
+ 1
5.23
6.19
7.87
10.5
15.8
31.6
w w w . a n a l o g i c t e c h . c o m
= 48.8V
Schottky Diode Selection
To ensure minimum forward voltage drop, high voltage
Schottky diodes are considered the best choice for the
White LED boost converter. The output diode is sized to
maintain acceptable efficiency and reasonable operating
junction temperature under full load operating condi-
tions. Forward voltage (V
tance (θ
ing a diode. The diode non-repetitive peak forward surge
current rating (I
load applications. I
duction period. Manufacturers’ datasheets should be
consulted to verify reliability under peak loading condi-
tions. The diode’s published current rating may not reflect
actual operating conditions and should be used only as a
comparative measure between similarly rated devices.
During the on-time, the output voltage on the output cap
is applied to the cathode of the external Schottky diode.
The rectifier's reverse breakdown voltage rating should
be greater than the maximum output voltage rating of
the Boost. 40V rated Schottky diodes are recommended
for outputs less than 30V, while 60V rated Schottky
diodes are recommended for outputs greater than 35V.
The average diode current is equal to the output cur-
rent.
The approximate power loss on the Schottky diode can
be determined:
Diode junction temperature can be estimated.
Output diode junction temperature should be maintained
below 110°C, but may vary depending on application
and/or system guidelines. The diode θ
with additional PCB area on the cathode. PCB heat-sink-
ing the anode may degrade EMI performance.
reverse leakage current of the rectifier must be consid-
ered to maintain low quiescent (input) current and high
efficiency under light load. The rectifier reversed current
increases dramatically at elevated temperatures.
JA
) are the dominant factors to consider in select-
P
LOSS-DIODE
T
FSM
J
= T
) should be considered for high pulsed
FSM
PRODUCT DATASHEET
AMB
rating drops with increasing con-
I
= I
AVG
+ θ
F
AVG
) and package thermal resis-
= I
JA
· V
OUT
· P
AAT1407
F
LOSS-DIODE
= I
OUT
JA
can be minimized
· V
1407.2010.06.1.0
F
The