RT9284B-15GJ6E Richtek USA Inc, RT9284B-15GJ6E Datasheet - Page 11

• Manufacturer Part Number: RT9284B-15GJ6E
• Description: IC LED DVR WHITE BCKLGT TSOT23-6
• Manufacturer: Richtek USA Inc

Specifications of RT9284B-15GJ6E

• Constant Current: Yes
• Internal Driver: Yes
• Type - Primary: Backlight, Flash/Torch
• Type - Secondary: White LED
• Mounting Type: Surface Mount
• Topology: PWM
• Number Of Outputs: 1
• Frequency: 900kHz ~ 1.5MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Package / Case: SOT-23-6 Thin, TSOT-23-6
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

Figure 7. Filtered PWM Signal for LED Dimming Control
The LED current can be calculated by the following
equation.
Inductor Selection
The recommended value of inductor for 3 to 5 WLEDs
applications are 4.7 to 22μH. Small size and better
efficiency are the major concerns for portable device, such
as RT9284A/B used for mobile phone. The inductor should
have low core loss at 1.2MHz and low DCR for better
efficiency. To avoid inductor saturation current rating should
be considered.
DS9284A/B-06 June 2009
2.7V to 5.5V
V
I
LED
EN
20
18
16
14
12
10
< 0.4V
8
6
4
2
0
=
V
0
V
IN
V
EN
FB
> 1.5V
10
C1
−
R2 (V
20
4.7uH to 22uH
2
6
4
×
VDD
EN
GND
30
RT9284A
PWM
L1
of RT9284A
R3 + R
R1
PWM Duty (%)
Figure 8
40
OVP
×
LX
FB
Duty V
2.8V
50
DC
1
5
3
0V
PWM Signal
SS0520
−
60
D1
FB
10k
R
3k
R3
70
DC
)
10k
80
R2
C2
1uF
C
DC
90
100
110
R1
I
LED
Capacitor Selection
Input and output ceramic capacitors of 1μF are
recommended for RT9284A/B applications. For better
voltage filtering, ceramic capacitors with low ESR are
recommended. X5R and X7R types are suitable because
of their wider voltage and temperature ranges.
Diode Selection
Schottky diode is a good choice for RT9284A/B because
of its low forward voltage drop and fast reverse recovery.
Using Schottky diode can get better efficiency. The high-
speed rectification is also a good characteristic of
Schottky diode for high switching frequency. Current rating
of the diode must meet the root mean square of the peak
current and output average current multiplication as
following :
The diode’ s reverse breakdown voltage should be larger
than the output voltage. SS0520 is recommended Schottky
diode for rectifier.
Layout Guide
A full GND plane without gap break.
VCC to GND noise bypass–Short and wide connection
for the 1μF MLCC capacitor between Pin6 and Pin2.
Minimized LX node copper area to reduce EMI.
Minimized FB node copper area and keep far away from
noise sources.
I
D
(RMS)
≈
(I
OUT
Figure 9. Top Layer
×
I
PEAK
)
RT9284A/B
www.richtek.com
11