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參數(shù)資料
| 型號： | T6309B-BX |
| 廠商： | TM Technology, Inc. |
| 英文描述： | Micropower Step-up DC/DC Converter |
| 中文描述： | 微功耗升壓型DC / DC轉(zhuǎn)換器 |
| 文件頁數(shù)： | 7/11頁 |
| 文件大?。?/td> | 131K |
| 代理商： | T6309B-BX |
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T6309B
Applications Information
Dimming Control
There are several types of dimming control
circuit as follows:
1. Using a PWM signal to CE pin
When using a PWM signal at CE pin, the
T6309B is turned on or off by the PWM
signal. The average LED current increases
proportionally with the duty cycle of the
PWM signal. The typical frequency range of
the PWM signal is 150Hz to 250Hz. The
magnitude of the PWM signal should be
greater than the threshold voltage of CE
voltage high.
2. Using a DC voltage
A DC voltage signal can be used as well to
control the LED brightness. The dimming
control method is shown in the figure 2.
When the DC voltage is zero, the LED is fully
turned on. As the DC voltage increases, the
voltage drop on R2 increases and the voltage
drop on R1 decreases. Thus the LED current
decreases. The selection of R1 and R2 should
make the current from the variable DC source
much smaller than the LED current and much
larger than the FB pin bias current.
For V
DC
range from 0V to 2V, the
selection of resistors in this figure gives
dimming control of LED current from 0mA to
20mA. Following steps are used to select the
resistor values:
Select the voltage V
MAX
to turn the LEDs
off. (e.g. 2.0V)
Select 0V as default to turn the LEDs fully
on.
Select the maximum LED current I
MAX
TM Technology Inc. reserves the right
P. 7
Publication Date: SEP. 2005
to change products or specifications without notice.
Revision: A
(e.g. 20mA) and 0mA as the minimum LED
current.
Calculate R2 to achieve a feedback current
in the range of I1 = 3uA to 10uA as the
LEDs are fully turned on:
R2 = V
REF
/ I1 (e.g. 0.4V/4uA =100KOhm )
Calculate R1 to meet the equation:
R1 / (R1+R2) = V
REF
/ V
MAX
(e.g. V
REF
=0.4V, V
MAX
=2.0V, R2=100KOhm,
the calculated R1 is 25KOhm)
Calculate the sense voltage Vs at maximum
LED current:
Vs = V
REF
x (1 + R1/R2)
(e.g. Vs = 0.4V x (1 + 25K/100K) = 0.5V)
Calculate the sense resistor Rs:
Rs = Vs / I
MAX
(e.g. 0.5V/20mA = 25 Ohm)
3. Using a Filtered PWM signal
The filtered PWM signal can be considered as
an adjustable DC voltage. It can be used to
replace the DC voltage source if adjustable
analog signal is not available in the system.
The circuit is shown in the figure below:
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