AAT1235IRN-T1 AnalogicTech, AAT1235IRN-T1 Datasheet - Page 14

• Manufacturer Part Number: AAT1235IRN-T1
• Description: High Efficiency White LED Drivers for Backlight and Keypad
• Manufacturer: AnalogicTech

Estimating Schottky Diode
Power Dissipation
The switching period is divided between ON and OFF
time intervals:
During the ON time, the N-channel power MOSFET is
conducting and storing energy in the boost inductor.
During the OFF time, the N-channel power MOSFET is
not conducting. Stored energy is transferred from the
input battery and boost inductor to the output load
through the output diode.
Duty cycle is defined as the ON time divided by the total
switching interval:
The maximum duty cycle can be estimated from the
relationship for a continuous mode boost converter.
Maximum duty cycle (D
input voltage (V
14
SwitchReg
Enable/Set
JP6
TM
IN(MIN)
3
2
1
Figure 3: A AAT1235-based High Efficiency White LED Driver Schematic.
VIN
D =
):
F
1
S
= T
MAX
= T
T
) is the duty cycle at minimum
ON
ON
ON
C1
2.2μF
T
⋅ F
+ T
ON
+ T
S
OFF
OFF
R2
187k
R3
12.1k
High Efficiency White LED Drivers for Backlight and Keypad
JP1
0
JP6
0
R1
22.6k
LED1
LED2
LED3
LED4
w w w . a n a l o g i c t e c h . c o m
JP2
0
JP7
0
LED6
LED7
LED8
LED9
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
1
2
3
4
5
6
7
8
U1
AAT1235 TDFN3X4
VIN
OV
EN/SET
B1
B2
RSET
IN
GND
VOUT
AGND
MBR0530T1
SW
The average diode current during the OFF time can be
estimated:
The V
average current during the off time. The average diode
current is equal to the output current:
The average output current multiplied by the forward
diode voltage determines the loss of the output diode:
For continuous LED currents, the diode junction tem-
perature can be estimated:
LIN
NC
NC
A1
A2
A3
SW_Node
16
15
14
13
12
11
10
9
2.2μH
D1
F
L1
of the Schottky diode can be estimated from the
T
J(DIODE)
RTN
P
JP3
0
JP8
0
LED11
LED12
LED13
LED14
LOSS(DIODE)
D
MAX
I
AVG(OFF)
= T
PRODUCT DATASHEET
I
AVG(TOT)
=
AMB
JP4
0
JP9
0
LED16
LED17
LED18
LED19
V
= I
= I
=
OUT
+ θ
1 - D
= I
AVG(TOT)
OUT
V
JA
- V
AAT1235
I
OUT
OUT
OUT
· P
· V
JP5
0
JP10
0
IN(MIN)
MAX
LED21
LED22
LED23
LED24
LOSS(DIODE)
F
· V
F
1235.2009.09.1.2
C2
2.2μF
25V