Electronic Components Datasheet Search |
|
EL7630 Datasheet(PDF) 6 Page - Intersil Corporation |
|
EL7630 Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 7 page 6 FN7371.1 February 22, 2006 For a required LED current ILED and chosen values of R1 and R2, the dimming DC voltage VDim can be expressed as: It is clear that as the required LED current ILED is closed to the rate current VFB/RSET, VDim is closed to VFB. As the required LED current is lower than the rate current, the dimming DC voltage VDim is increased in R2/R1 factor. Open-Voltage Protection In some applications, it is possible that the output is opened, e.g. when the LEDs are disconnected from the circuit or the LEDs fail. In this case the feedback voltage will be zero. The EL7630 will then switch to a high duty cycle resulting in a high output voltage, which may cause the LX pin voltage to exceed its maximum 27V rating. To implement overvoltage protection, a zener diode Dz and a resistor R1 can be used at the output and FB pin to limit the voltage on the LX pin as shown in Figure 10. It is clear that as the zener is turned on, due to the overvoltage, the zener diode’s current will set up a voltage on R1 and RSET and this voltage is applied on FB pin as the feedback node. This feedback will prevent the output from reaching the overvoltage condition. In the overvoltage protection circuit design, the zener voltage should be larger than the maximum forward voltage of the LED string. Components Selection The input capacitance is normally 0.22µF~4.7µF and the output capacitor is 0.22µF~1µF. X5R or X7R type of ceramic capacitor with the correct voltage rating is recommended. The output capacitor value will affect PWM dimming performance. For lower output capacitor values, the range of PWM dimming is wider than for higher values of output capacitor. When choosing an inductor, make sure the inductor can handle the average and peak currents given by the following formulas (80% efficiency assumed): Where: • ∆IL is the peak-to-peak inductor current ripple in Ampere • L inductance in H. •fOSC switching frequency, typically 1.2MHz The boost inductor can be chosen in a wide range of inductance (10µH~82µH). For 10µH inductor value, the boost inductor current will be in discontinuous mode. As the inductor value decreases further, the ripple of the boost inductor current is increased and can even trigger overcurrent protection. For high boost inductor value, the boost inductor current will be in continuous mode. For general boost converter, as the converter operates in continuous mode, there is right half plane zero (RHPZ). If RHPZ frequency is less than or close to the control loop crossover frequency, there is a stability issue. In EL7630, the compensation network is well designed and there is no RHPZ stability issue even if the inductor value is over 82µH. For the same series of inductors, a lower inductance has lower DC resistance (DCR), which causes less conducting loss, but higher peak to peak current variation, which generates more RMS current loss. Figure 11 shows the efficiency of the demo board with different LED load for a specific series of inductor. The diode used should be a schottky type with minimum reverse voltage of 28V. The diode’s peak current is the same as the inductor’s peak current. The schottky RMS current is: EL7630 C1 VDD LX ENAB FB GND L1 22µH D1 C2 0.22µF RSET 4.75 Ω OFF/ON LEDs 1µF LX VIN 2.7V~5.5V R1 R2 DIMMING SIGNAL FIGURE 9. ANALOG DIMMING CONTROL APPLICATION CIRCUIT VDim VFB VFB ILED – RSET ⋅ () + R2 R1 ------- ⋅ = (EQ. 5) EL7630 C1 L1 22µH D1 C2 0.22µF RSET 4.75 Ω 2.7V~5.5V OFF/ON LEDs 1µF VDD LX ENAB FB GND VIN R1 Dz FIGURE 10. LED DRIVER WITH OVERVOLTAGE PROTECTION CIRCUIT ILAVG ILED VOUT ⋅ 0.8 VIN ⋅ --------------------------------- = (EQ. 6) ILPK ILAVG 1 2 --- IL ∆ ⋅ + = (EQ. 7) IL ∆ VIN VOUT VIN – () ⋅ LVOUT fOSC ⋅⋅ --------------------------------------------------- = (EQ. 8) IRMS D2 ILAVG 2 ⋅ 1 6 --- IL 2 ∆ ⋅ + ⋅ = (EQ. 9) EL7630 |
Similar Part No. - EL7630 |
|
Similar Description - EL7630 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
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 |