BD6590MUV
Technical Note
●LED current setting range
LED current can set up Normal current by resistance value (RISET) connecting to ISET voltage.
Setting of each LED current is given as shown below.
Normal current = 432/RISET (A)
Also, Normal current setting range is 10mA~30mA. LED current becomes a leak current MAX 2µA at OFF setting.
When using beyond current setting range, please be careful that the error in LED current setting could be large.
ISET Normal current setting example
RISET
LED current
24.0mA
19.6mA
18.0mA
16.0mA
14.4mA
13.1mA
18kꢀ (E24)
22kꢀ (E24)
24kꢀ (E24)
27kꢀ (E24)
30kꢀ (E24)
33kꢀ (E24)
●Brightness control
There are two dimming method is available, first method is analog dimming that apply analog voltage to ISET terminal, and
second method is PWM control via digital dimming of PWMPOW or PWMDRV. Because each method has the different merit,
please choose a suitable method for the application of use.
Two techniques can be used as digital dimming by the PWM control One is PWM control of current driver, the other is PWM
control of power control.
As these two characteristics are shown in the below, selects to PWM control process comply with application.
・Efficiency emphasis in the low brightness which has an influence with the battery life
・LED current dispersion emphasis in the PWM brightness control
(Reference)
→ 2) Power control PWM control
→ 1) Current driver PWM control
Efficiency of LED current 0.5mA
(PWM Duty=2.5%)
PWM frequency 200Hz
Limit dispersion capability of low duty
PWM regulation process
Current driver
Power control
74.8%
91%
0.04%
0.40%
1) Current driver PWM control is controlled by providing PWM signal to PWMDRV, as it is shown Fig.14.
The current set up with ISET is chosen as the H section of PWMDRV and the current is off as the L section. Therefore, the
average LED current is increasing in proportion to duty cycle of PWMDRV signal. This method that it lets internal circuit
and DC/DC to 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 5µs (MIN0.1% at 200Hz). And, don't use for the brightness
control, because effect of ISET changeover is big under 1µs ON time and under 1µs OFF time. Typical PWM frequency is
100Hz~25kHz.
PWMDRV
ON
ON
ON
OFF
OFF
OFF
ON
LED current
Coil current
IC’s active current
Fig.14 PWMDRV sequence
2) Power control PWM control is controlled by providing PWM signal to PWMPOW, as it is shown Fig.15. The current setting
set up with PWMDRV logic is chosen as the H section and the current is off as the L section. Therefore, the average LED
current is increasing in proportion to duty cycle of PWMPOW signal. This method is, because IC can be power-off at
off-time, the consumption current can be suppress, and the high efficiency can be available, so it makes it possible to
brightness control until 50µs (MIN1% at 200Hz). And, don't use for the brightness control, because effect of power
ON/OFF time changeover is big under 50µs ON time and under 50µs OFF time.
Typical PWM frequency is 100Hz~1kHz.
PWMPOW
ON
ON
ON
ON
OFF
OFF
OFF
OFF
LED current
Coil current
IC’s active current
Fig.15 PWMPOW sequence
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2011.07 - Rev.B
12/26
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