Technical Note
12/22
BD60A00NUX, BD60A60NUX
www.rohm.com
2011.12 - Rev.A
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3) When Schottky diode(SBD) remove
In the situation that connection is opened and also DC/DC is activated, SW terminal voltage becomes more than rated
voltage due to a lack of parts that can accept the current accumulated inside the coil. Consequently IC might be
destroyed. To prevent the IC destruction, SBD open protection is functioned. SW terminal is never destroyed as
boosting operation is stopped after VOUT terminal detects less than 0.2V.
4) When resistance linked to an ISET terminal short-circuits
Since Resistor connected to ISET terminal becomes 0
Ω
, LED current setting value becomes more than rating. In order
to avoid this trouble, this IC has LED current limit protection. By using this function, setting current of rating current
driver becomes 0mA, and the current flow of LED is almost same as leak current.
●
Control signal input timing
When input control signals such as Enable and PWM without completing the standup of supply voltage (VIN), be
careful of the following points.
①
Input each control signal after VIN exceeds 2.2V and UVLO is off.
②
When input Enable and PWM, the standup time should be placed as Min.100µs from 2.2V to stable voltage for
VIN.
③
Since a soft start function stops working at the time of following PWM=H when EN=H is held with PWM=L.
After EN=H should input a PWM signal within 10ms.
●
Start control (EN) and select LED current driver (PWM)
This IC can control the IC system by EN terminal and also turns off compulsorily by setting “L” level input voltage 0.4V or
below. It also powers on when EN becomes more than “H” level input voltage 1.4V. In the case of EN=H, LED current fixed
by ISET resistor with PWM=H flows. When it is selected at PWM=L, LED current stop to flow.
EN PWM
IC
LED
current
L L
Off
Off
H L
On
Off
L H
Off
Off
H
H
On
Current fixed by ISET
●
LED current setting range
LED current sets up normal current by resister (RISET) connected to ISET voltage.
Each setting current is shown as below.
Normal current = 600/RISET [A]
Normal current setting range is 10mA~30mA, and also LED current at off setting is MAX 2µA of leak current.
ISET Normal current setting example
RISET LED
current
20.0k
Ω
(E96)
30.0mA
24.0k
Ω
(E24)
25.0mA
30.0k
Ω
(E24)
20.0mA
56.0k
Ω
(E24)
10.7mA
VIN
①
2.2V
EN
②
Min. 100
µs
PWM
DC/DC VOUT
Fig.11 Control signal input timing
VIN
EN
③
Min. 10
ms
PWM
DC/DC VOUT