BD60A00NUX Datasheet, PDF (13/23 Pages) Rohm – White Backlight LED Drivers for Small to Medium LCD Panels (Switching Regulator Type)

BD60A00NUX, BD60A60NUX
Technical Note
●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.
L1
10μH
Vin
2.7V to 4.6V
Cout
30
Cin
4.7μF
2.2μF
25
PWM Input
Vin SW
PWM
Vout
25mA
20
RESET
EN
15
FB
ISET
10
R1
GND
24kΩ
5
PWM
LED current
ON
OFF
ON
OFF
0
0 20 40 60 80 100
PWM Hi duty [%]
Coil current
ON
OFF
IC’s active current
ON
Fig.12 PWM sequence
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
Vin
2.7V to 4.6V
L1
10μH
Cout
Cin
2.2μF
4.7μF
30
Vin SW
Vout
LED ON/OFF
PWM
25
RESET
EN
20
R2 22kΩ
FB
DC
ISET
15
GND
R1
470kΩ
10
LED current =
1000 x 0.6V
470kΩ
+
1000
22kΩ
0.6V - DAC output
5
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
DC Voltage [V]
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13/22
2011.12 - Rev.A