Technical Note
18/22
BD60A00NUX, BD60A60NUX
www.rohm.com
2011.12 - Rev.A
© 2011 ROHM Co., Ltd. All rights reserved.
●
PCB Layout
In order to make the most of the performance of this IC, its PCB layout is very important. Characteristics such as efficiency
and ripple and the likes change greatly with PCB layout, which please note carefully
<Input capacitor Cin (1
μ
F) for coil>
Connect input capacitor Cin (1
μ
F) as close as possible between coil L1 and GND.
<Schottky barrier diode SBD>
Connect schottky barrier diode SBD as close as possible between coils L1and SW pin.
<Output capacitor Cout>
Connect output capacitor Cout between cathode of SBD and GND.
Make both GND sides of Cin and Cout as close as possible.
<LED current setting resistor RISET(24k
Ω
)>>
Connect LED current setting resistor RISET(24k
Ω
) as close as possible between ISET pin and GND.
There is possibility to oscillate when capacity is added to ISET terminal, So pay attention that capacity isn’t added.
<Heat radiation of back side PAD>
PAD is used for improving the efficiency of IC heat radiation. Solder PAD to GND pin.
Moreover, connect ground plane of board using via as shown in the patterns of next page.
The efficiency of heat radiation improves according to the area of ground plane.
<Others>
When those pins are not connected directly near the chip, influence is give to the performance of BD60A00NUX, and
may limit the current drive performance. As for the wire to the inductor, make its resistance component small so as to
reduce electric power consumption and increase the entire efficiency.
The PCB layout in consideration of these is shown in the next page.
SW
Vin
Cin
4.7
μ
F
RISET
24k
Ω
Cout
2.2
μ
F
25mA
Vin
2.7V to 4.6V
Vout
FB
L1
10
μ
H
ISET
GND
EN
PWM
RESET
PWM Input