
BD6581GU
Datasheet
● The Coil Selection
The DC/DC is designed by more than 4.7μH. When L value sets to a lower value, it is possibility that the specific
sub-harmonic oscillation of current mode DC / DC will be happened. Please do not let L value to 3.3μH or below.
And, L value increases, the phase margin of DC / DC becomes to zero. Please enlarge the output capacitor value when you
increase L value.
Example)
4.7μH = output capacitor 2.2μF/50V 1pcs
6.8μH = output capacitor 2.2μF/50V 2pcs
10μH = output capacitor 2.2μF/50V 3pcs
This value is just examples, please made sure the final judgment is under an enough evaluation.
● Layout
In order to make the most of the performance of this IC, its layout pattern is very important. Characteristics such as
efficiency and ripple and the likes change greatly with layout patterns, which please note carefully.
to Anode of each LED
E
LED6
LED5
LED4
LED3
LED2
Reset
C BAT
D
PWM
RSTB
GND
FAILSEL
GND
LED1
C
C REG
VBAT
PWMPOW
VREG
ISETL
PWMDRV
B
A
TEST
ISETH
GND
VDET
SW
SENSP
SENSN
1
2
3
4
5
Tr
C IN
L
SBD
C OUT
R SENSE
to Cathode of LED
to GND
Figure 40. Layout
Connect the input bypath capacitor CIN(10μF) nearest to coil L, as shown in the upper diagram.
Wire the power supply line by the low resistance from CIN to VBAT pin. Thereby, the input voltage ripple of the IC can be
reduced. Connect smoothing capacitor CREG of the regulator nearest to between VREG and GND pin, as shown in the
upper diagram. Connect schottky barrier diode SBD of the regulator nearest to between coil L and switching transistor Tr.
And connect output capacitor COUT nearest to between CIN and GND pin. Thereby, the output voltage ripple of the IC can
be reduced.
Connect switching transistor Tr nearest to SW pin. Wire coil L and switching transistor Tr, current sensing resistor R SENSE by
the low resistance. Wiring to the SENSP pin isn't Tr side, but connect it from R SENSE side. Over current value may become
low when wiring from Tr side. Connect R SENSE of GND side isolated to SENS pin. Don’t wire between R SENSE and SNESN
pin wiring from R SENSE pin to GND pin. And R SENSE GND line must be wired directly to GND pin of output capacitor. It
has the possibility that restricts the current drive performance by the influence of the noise when other GND is connected to this
GND.Connect LED current setting resistor RISET nearest to ISET pin. There is possibility to oscillate when capacity is
added to ISET terminal, so pay attention that capacity isn't added. And, RISET of GND side must be wired directly to
GND pin. When those pins are not connected directly near the chip, influence is given to the performance of BD6581GU,
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.
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TSZ02201-0G3G0C400170-1-2
03.Dec.2012 Rev.001