 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
ISL78100 Datasheet(PDF) 11 Page - Intersil Corporation |
|
|
|||||||||||||||||||||||||||||
ISL78100 Datasheet(HTML) 11 Page - Intersil Corporation |
|
|
11 / 19 page  11 FN6626.0 December 17, 2007 Theory of Operation General Description The ISL78100 is a flexible, highly integrated high-power LED driver consisting of a PWM switching controller and integrated 36V NDMOS power FET. The device can drive up to 8 series high-power LED's at currents up to 1A at 16V input or 5 LEDs at current up to 350mA at 2.7V input. The control loop can be configured as either a boost or buck regulator with the configuration of the BUCK/BOOSTN pin, providing an output voltage above or below the input supply voltage, depending on the number of stacked LEDs. The controller operates from 2.7V to 16V depending on the numbers of LEDs and current required and can be powered by a single lithium ion battery, 5V or 12V regulated supplies or automotive electrical systems. LED current is sensed through a low value resistor in series with the LED. A thermistor can be used to implement a thermal protection scheme to limit the maximum LED temperature to a preset desirable level. Switching Regulator The ISL78100 employs a current mode PWM control scheme with a nominal switching frequency of 1MHz. This provides fast transient response and enables the use of low profile inductors and compact multilayer ceramic capacitors. Settling time is optimized by the use of a simple control loop without an error amplifier, relying instead on intrinsic gain within the direct summing path. Due to the lower loop gain, offset must be accounted for when setting up initial LED bias current. Refer to the “Application Configurations” on page 11 of the datasheet for further information. Figure 28 shows a block diagram of the system. Application Configurations Operating Modes The ISL78100 can operate as either a buck or boost regulator. Hardwire BUCK/BOOSTN to GND for boost mode or to VDC for buck mode. In buck mode the power NDMOS drive circuit is "floated" (boot-strapped) allowing the NDMOS gate to be driven above VIN to fully enhance the power NDMOS. An internal Schottky diode between VDC (5V) and VHI reduces external component count. Use a ceramic capacitor of at least 50nF between VHI and SWS1/2 to bootstrap VHI. LED Load Connection ISL78100 includes an auto-sensing FB level shift circuit that enables the LED load to be connected to either GND or VIN. An internal sense circuit monitors the FB pin voltage. When the level exceeds VDC/2, the feedback reference voltage is switched from GND to VIN. Refer to the application section of the datasheet for typical application schematics. Start-up To maximize external PWM switching speed, the ISL78100 does not include an internal soft-start circuit. When VDC exceeds the power-on reset threshold, switching is delayed for 1ms (tDELAY) allowing the output capacitor to charge through the inductor. If soft-start control is required, a suitable application circuit is shown in Figure 30. Light Level Control Two light control schemes are provided: 1. An external PWM signal via the EN/PWM pin, providing low frequency PWM dimming. 2. Bias current level adjustment via the LEVEL input or fixed internal bias. PWM Dimming LED color temperature varies with bias current. In backlighting applications, PWM dimming offers better control of color temperature because current through the LEDs is kept constant. A 5V gate driver (ENL) synchronized to EN/PWM can be used to control an external N-Channel FET and disconnect the LED stack during the PWM off-period. The switch prevents discharge of the output capacitor by the LED load, maintaining a constant bias independent of PWM duty cycle. Operation at 1kHz PWM rate is shown in Figure 31 and Figure 32. The load disconnect switch improves PWM dynamic range, linearity and color temperature control. To further improve the linearity of PWM dimming, an internal timer delays system shutdown via EN/PWM for 50ms. FIGURE 29. FB REFERENCE AUTO SWITCH LEVEL SHIFT ISL78100 GND VIN FB + - VOLTAGE FEEDBACK VDC/2 FIGURE 30. EXTERNAL SOFT-START CIRCUIT COUT 20µF R1 100 VIN FB SWS1 SWS2 SWD1 SWD2 VBAT FAULT ISL78100 VBAT VOUT C1 4.7nF R2 2k L1 10µH RSENSE 0.5 ISL78100 |
Similar Part No. - ISL78100 |
|
Similar Description - ISL78100 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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
