ISL97631 INTERSIL | Alldatasheet

Document overview

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Technical content

Features

  • Up to 6 LEDs in series
  • 27V maximum output
  • 2.7V to 5.5V input
  • Up to 85% efficient
  • 1.35MHz constant frequency
  • Enable/PWM dimming control
  • Pb-free plus anneal available (RoHS compliant)

Applications

  • LED backlighting
  • Cell phones
  • PDAs
  • Handheld games
  • MP3 players
  • GPS
  • Other handheld devices VOUT GND LX VIN ENAB 5 FB

Ordering Information

PCS. TAPE & REEL PACKAGE (TAPE AND REEL) PKG. DWG. # ISL97631IHTZ-T7 (See Note) 631Z 3,000

6 Ld TSOT (Pb-free)

ISL97631IHTZ-T7A (See Note) 631Z 270 NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. Data Sheet December 21, 2005 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2005. All Rights Reserved All other trademarks mentioned are the property of their respective owners.

FN7370.1 December 21, 2005 Absolute Maximum Ratings (TA = 25°C) Thermal Information Thermal Resistance (Typical, Note 1) θJA (°C/W) 190 (TSOT - Lead Tips Only) CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed over the specified temperature range. All parameters are based on pulsed tests, therefore: TJ = TC = TA NOTE: 1. θJA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details. Electrical Specifications VIN = 3V, VENAB = 3V, TA = -40°C to 85°C unless otherwise specified. PARAMETER

DESCRIPTION

VOUT = 16V, ILED = 20mA 2.7 V VIN-MAX Maximum Operating Voltage VOUT = 25V, ILED = 20mA 5.5 V VFB Feedback Voltage 100 120 mV IFB FB Pin Bias Current 100 nA IIN Supply Current ENAB = 3V, output not switching 0.6 1.0 mA ENAB = 0V µA FOSC Switching Frequency 0.8 1.35 1.8 MHz DMAX Maximum Duty Cycle TA = 25°C ILIM Switch Current Limit TA = 25°C 280 350 mA 250 350 mA rDS(ON) Switch On Resistance ILX = 100mA 750 mΩ ILEAK(LX) Switch Leakage Current VLX = 27V, Vout = 27V 0.01 µA ILEAK(VOUT) Diode Leakage Current VOUT = 27V 0.01 µA VDIODE LX-VOUT Diode Forward Voltage IDIODE = 100mA, TA = 25°C 0.75 0.9 V VENAB-HI ENAB Voltage High 2.5 V VENAB-LO ENAB Voltage Low 0.6 V IENAB ENAB Pin Bias Current µA ∆ILED/∆VIN Line Regulation VIN = 2.7V to 5V 0.2 %/V Eff Efficiency ILED = 20mA, 3 LEDs ISL97631

FN7370.1 December 21, 2005 Block Diagram Detailed Description The ISL97631 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. It can drive up to 6 LEDs in series or 15 LEDs in parallel/series configuration, with efficiencies of up 85%. The ISL97631 operates from an input voltage of 2.7V to 5.5V and can boost up to 27V. Steady-State Operation The ISL97631 operates with constant frequency PWM. The switching frequency is around 1.35MHz. Depending on the input voltage, inductance, number of LEDs and the LED current, the converter operates in either continuous conduction mode or discontinuous conduction mode. Both are normal. The forward current of the LED is set using the RSET resistor. In steady state mode, this current is given by the equation: Shut-Down When taken low the ENAB pin places the ISL97631 into power down mode. When in power down, the supply current is reduced to less than 1µA. Dimming Control PWM DIMMING The ENAB pin also doubles as a brightness control. There are two different possible dimming control methods. The first dimming method is controlled through the duty-cycle of the ENAB input PWM waveform, which can operate at frequencies up to 1kHz. For frequencies greater than 1kHz, see Analog Dimming. The LEDs operate at either zero or full current. This is the PWM dimming control method. The relationship between the average LED current and the duty-cycle (D) of the ENAB pin’s waveform is as follows: FIGURE 7. ISL97631 BLOCK DIAGRAM Output Pin. Connect to the anode of the top LED and the output filter capacitor . GND Ground Pin. Connect to local ground. LX Switching Pin. Connect to inductor. ENAB Enable Pin. Connect to enable signal to turn-on or off the device. FB Feedback Pin. Connect to the cathode of bottom LED and the sense resistor. VIN Input Supply Pin. Connect to the input supply voltage, the inductor and the input supply decoupling capacitor. ILED VFB RSET (EQ. 1) average ILED VFB RSET (EQ. 2) ISL97631

voltage will be greater for lower values.

  • ∆IL is the peak-to-peak inductor current ripple in Amps
  • L is the inductance in H.
  • fOSC is the switching frequency, typically 1.35MHz The ISL97631 supports a wide range of inductance values (22µH~82µH). For lower inductor values or lighter loads, the boost inductor current may become discontinuous. For high boost inductor values, the boost inductor current will be in continuous mode. The demo board efficiency bench test results are shown in

Figure 11. The input voltage is 4V and curves are shown for 2, 3, 4, 5 and 6 LEDs (boost inductor L = 22µH). enables up to 6 LEDs to be placed in series. be used to balance LED currents. currents due to manufacturing and temperature differences. FB pin and the primary LED string. FIGURE 10. LED DRIVER WITH OVERVOLTAGE

0.8 VIN

FIGURE 11. EFFICIENCY CURVE WITH 2, 3, 4, 5 AND 6 LEDs FIGURE 12. LEDs IN SERIES/PARALLEL WITH MIRROR

FN7370.1 December 21, 2005 PCB Layout Considerations The layout is very important for the converter to function properly. RSET must be located as close as possible to the FB and GND pins. Longer traces to the LEDs are OK. Similarly, the supply decoupling cap and the output filter cap should be as close as possible to the VIN and VOUT pins. The heat of the IC is mainly dissipated through the GND pin. Maximizing the copper area connected to this pin is preferable. In addition, a solid ground plane is always helpful for the EMI performance. The demo board is a good example of layout based on the principle. Please refer to the ISL97631 Application Brief for the layout. ISL97631

All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com FN7370.1 December 21, 2005 ISL97631 Package Outline