 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
RT9271 Datasheet(PDF) 10 Page - Richtek Technology Corporation |
|
|
|||||||||||||||||||||||||||||
RT9271 Datasheet(HTML) 10 Page - Richtek Technology Corporation |
|
|
10 / 15 page  RT9271 10 DS9271-13 March 2007 www.richtek.com Figure 6. Recommended Soft-Start Circuit Application Information LED Current Control The RT9271 regulates the LED current by setting the current sense resistor (R2) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily. In order to have an accurate LEDcurrent, precision resistors are preferred (1% is recommended). The table for R2 selection is shown below. LED I V 25 . 0 2 R = Dimming Control a. Using a PWM Signal to EN Pin For controlling the LEDbrightness, the RT9271 can perform the dimming control by applying a PWM signal to EN pin. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly. b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 5. According to the Superposition Theorem, as theDC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in Figure 5 sets dimming control of LED current from 20mA to 0mA. Figure 5. Dimming Control Using a DC Voltage ILED (mA) R2 (Ω) 5 49.9 10 24.9 12 21 15 16.5 20 12.4 R2 Resistor Value Selection Figure 4. PWM Dimming Control Using the EN Pin Condition Inductance (H) Schottky Diode 2 WLEDs 4.7u~10u SS0520 3 WLEDs 4.7u~10u SS0520 Recommended Inductance and Rectifier (for Li-Ion cell) VCC EN GND LX FB RT9271 PWM signal C1 1uF C3 1uF D1 SS0520 LX 10uH R2 12 OVP D2 D4 D3 V IN 2.4 to 6V VCC EN GND LX FB RT9271 C1 1uF C3 1uF LX 10uH R2 12 OVP D2 D4 D3 VDC Dimmimg 0 to 2.8V R4 82k R3 6.8k D1 SS0520 V IN 2.4 to 6V VCC EN GND LX FB RT9271 PWM signal C1 1uF C3 1uF D1 SS0520 LX 10uH R2 12 OVP D2 D4 D3 C6 10nF R6 10k R5 1k V IN 2.4 to 6V |
Similar Part No. - RT9271 |
|
Similar Description - RT9271 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
