Technical Note
13/22
BD60A00NUX, BD60A60NUX
www.rohm.com
2011.12 - Rev.A
© 2011 ROHM Co., Ltd. All rights reserved.
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Brightness control
There are two dimming method available; the first method is analog dimming that applies analog voltage to ISET terminal,
and the second method is digital dimming that inputs PWM to PWM terminal.
Since each method has the different merits,
please choose a suitable method for the application of use.
1) Current driver PWM control is controlled by providing PWM signal to PWM, as it is shown Fig.12.
The current set up with ISET is chosen as the H section of PWM and the current is off as the L section. Therefore, the
average LED current increases in proportion to duty cycle of PWM signal. This method that internal circuit and DC/DC
work, because it becomes to switch the driver, the current tolerance is a few when the PWM brightness is adjusted, so
it makes it possible to brightness control until 0.4µs (MIN1% at 25kHz). And, don't use for the brightness control,
because effect of ISET changeover is big under 0.4µs ON time and under 3µs OFF time. Typical PWM frequency is
100Hz~25kHz.
2) Analog dimming can be operated by applying voltage to ISET terminal via resistor as the below figure shows. ISET
terminal voltage works to become 0.6V regardless of the connected resistor. LED current increases ISET terminal
current 600 times, so that LED current can be minimized by decreasing flow current into ISET terminal using external
DC input
LED current =
1000 x 0.6V
470k
Ω
+
22k
Ω
1000
0.6V - DAC output
PWM
LED current
Coil current
IC’s active current
ON
OFF
ON
OFF
ON
OFF
ON
Fig.12 PWM sequence
SW
Vin
Cin
4.7
μ
F
R1
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
0
5
10
15
20
25
30
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7
DC Voltage [V]
LED Current [mA]
0
5
10
15
20
25
30
0
20
40
60
80
100
PWM Hi duty [%]
LED Current [mA]
SW
Vin
Cin
4.7
μ
F
R1
470k
Ω
Cout
2.2
μ
F
Vin
2.7V to 4.6V
Vout
FB
L1
10
μ
H
ISET
GND
EN
PWM
LED ON/OFF
RESET
DC
R2 22k
Ω