Electronic Components Datasheet Search |
|
ISL97632IRT14Z-T Datasheet(PDF) 7 Page - Intersil Corporation |
|
ISL97632IRT14Z-T Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 9 page 7 FN9239.2 April 10, 2007 Applications Efficiency Improvement Figure 2 shows the efficiency measurements. The choice of the inductor has a significant impact on the power efficiency. As shown in Equation 4, the higher the inductance, the lower the peak current therefore the lower the conduction and switching losses. On the other hand, it has also a higher series resistance. Nevertheless, the efficiency improvement from lowering the peak current is greater than the impact of the resistance increase with larger value of inductor. Efficiency can also be improved for systems that have high supply voltages. Since the ISL97632 can only supply from 2.4V to 5.5V, VIN must be seperated from the high supply voltage for the boost circuit as shown in Figure 7 and the efficiency improvement is shown in Figure 8. 8 LEDs Operation For medium size LCDs that need more than 6 low power LEDs for backlighting, such as a Portable Media Player or Automotive Navigation Panel displays, the voltage range of the ISL97632 is not sufficient. However, the ISL97632 can be used as an LED controller with an external protection MOSFET connected in cascode fashion to achieve higher output voltage. A conceptual 8 LEDs driver circuit is shown in Figure 9. A 60V logic level N-Channel MOSFET is configured such that its drain ties between the inductor and the anode of schottky diode, its gate ties to the input, and its source ties to the ISL97632 LX node connecting to the drain of the internal switch. When the internal switch turns on, it pulls the source of M1 down to ground, and LX conducts as normal. When the internal switch turns off, the source of M1 will be pulled up by the follower action of M1, limiting the maximum voltage on the ISL97632 LX pin to below Vin, but allowing the output voltage to go much higher than the breakdown limit on the LX pin. The switch current limit and maximum duty cycle will not be changed by this setup, so input voltage will need to be carefully considered to make sure that the required output voltage and current levels are achievable. Because the source of M1 is effectively floating when the internal LX switch is off, the drain-to-source capacitance of M1 may be sufficient to capacitively pull the node high enough to breaks down the gate oxide of M1. To prevent this, VOUT should be connected to VIN, allowing the internal schottky to limit the peak voltage. This will also hold the VOUT pin at a known low voltage, preventing the built in OVP function from causing problems. This OVP function is effectively useless in this mode as the real output voltage is outside its intended range. If the user wants to implement their own OVP protection (to prevent damage to the output capacitor, they should insert a zener from vout to the FB pin. In this setup, it would be wise not to use the FBSW to FB switch as otherwise the zener will have to be a high power one capable of dissipating the entire LED load power. Then the LED stack can then be connected directly to the sense resistor and via a 10k resistor to FB. A zener can be placed from Vout to the FB pin allowing an over voltage event to pull up on FB with a low breakdown current (and thus low power zener) as a result of the 10k resistor. SEPIC Operation For applications where the output voltage is not always above the input voltage, a buck or boost regulation is needed. A SEPIC (Single Ended Primary Inductance Vs = 12V L1 22µ 1 2 R1 4 Ω C3 0.22µ D2 D3 D1 D5 D6 D4 ISL97632 FBSW LX VOUT SDIN VIN FB GND C1 1µ 25mA C2 0.1µ EN VIN = 2.7V TO 5.5V FIGURE 7. SEPERATE HIGH INPUT VOLTAGE FOR HIGHER EFFICIENCY OPERATION 510 15 20 90 85 70 0 75 80 25 30 ILED (mA) VIN = 4V 6 LEDs L1 = 22µH R1 = 4 Ω VS = 12V VS = 9V FIGURE 8. EFFICIENCY IMPROVEMENT WITH 9V AND 12V INPUTS VOUT LX ISL97632 SDIN VIN FBSW GND FB EN R1 6.3 Ω D3 D4 D5 D6 D7 D8 L1 2.2µ 12 VIN = 2.7V TO 5.5V C3 4.7µ D0 10BQ100 M1 FQT13N06L D1 C1 1µ SK011C226KAR C2 0.1µ D2 FIGURE 9. CONCEPTUAL 8 LEDS HIGH VOLTAGE DRIVER ISL97632 |
Similar Part No. - ISL97632IRT14Z-T |
|
Similar Description - ISL97632IRT14Z-T |
|
|
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 |