AAT1235 Datasheet, PDF (14/21 Pages) Advanced Analogic Technologies – High Efficiency White LED Drivers for Backlight and Keypad

AAT1235
High Efficiency White LED Drivers
for Backlight and Keypad
If four LEDs are connected in series on one chan-
nel, the total V_F from the WLEDs could be as high
as 18.8V. Therefore, using R3 = 12.1kΩ and setting
V_{OUT(PROTECTION)} = 20V is recommended. Selecting
a 1% resistor, this results in R2 = 187kΩ (rounded to
the nearest standard 1% value).
It is always recommended to use the same number
of WLEDs on each channel and set the appropriate
over-voltage protection. Failure to do so may cause
any one of the (5) sink pins to exceed the absolute
maximum rating voltage and permanently damage
the device in case the channel is disconnected
(open circuit failure). Examples of over voltage set-
tings for various strings of series-connected LEDs
are shown in Table 7.
Number of WLEDs
on Each Channel
4
3
2
Total Maximum V_F (V)
18.8
14.1
9.4
V_{OUT(PROTECTION)} (V)
20
15
10
R3 = 12.1kΩ
R2 (kΩ)
187
140
88.7
Table 7: Over-Voltage Protection Settings.
VIN
JP6
3
2
1
Enable/Set
R2
187k
JP1
0
LED1
LED2
LED3
LED4
JP6
0
C1
2.2µF
R3
12.1k
R1
22.6k
VOUT
JP2
0
LED6
LED7
D1
MBR0530T1
LED8
SW_Node
LED9
L1
JP7
0
U1
2.2µH
AAT1235 TDFN3X4
1
2
3
4
5
6
7
8
VIN
LIN
OV
A1
EN/SET A2
B1
A3
B2 AGND
RSET NC
IN
NC
GND
SW
16
15
14
13
12
11
10
9
JP3
0
LED11
JP4
0
LED16
JP5
0
LED21
LED12
LED13
LED14
LED17
LED18
LED19
LED22
LED23
C2
2.2µF
25V
LED24
JP8
JP9
JP10
0
0
0
RTN
L1: 2.2uH Taiyo Yuden NR4018T2R2M
C1: 0805 10V 2.2µF X7R GRM21BR71A225KA01
C2: 0805 25V 2.2µF X7R GRM21BR71E225KA73L
LED1-24: OSRAM LW M673 or equivalent
Figure 3: A AAT1235-based High Efficiency White LED Driver Schematic.
14
1235.2007.02.1.1