| Features, Applications |
FEATURES s Low quiescent ground current (0.5mA typical) s Power efficiency over 80% s Compatible pinout with LT1937 s Adjustable output current (up 40mA) s High frequency 1.2MHz operation s Input voltage operation down 2.5V s Low resistance (0.5) power switch s Drives to 4 White LEDs in series s Shutdown current less than 1�A s Load fault protection against open-circuits s Low value external components s Low profile SOT23 (1mm max) and APPLICATIONSs Color LCD and keypad backlighting s Cellular phones s Handheld terminals s Digital cameras s PDAs/Games s Portable MP3 players DESCRIPTIONThe is a DC/DC step up converter that delivers a regulated output current. Operation at a constant switching frequency of 1.2MHz allows the device to be used with very small value external inductor and ceramic capacitors. The CAT37 is targeted to drive multiple white lightemitting diodes (LEDs) connected in series and provides the necessary regulated current to control the brightness and the color purity. An external resistor R1 controls the output current level. LED currents to 40mA can be supported over a wide range of input supply voltages from to 7V, making the device ideal for batterypowered applications. A high voltage output stage allows to 4 White LEDs to be driven in series. Series drive provides inherent current matching. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown input pin allows the device to be placed in power-down mode with "near zero" quiescent current. In addition to overcurrent limiting protection, the device also includes detection circuitry to ensure protection against open-circuit load fault conditions. The device is available in a low profile (1mm max height) 5-lead thin SOT23 package and in a TDFN (0.8mm max height) package. C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 D1: Zetez ZHCS400 L1: Panasonic ELJEA6R8 or equivalent Figure 1. Driver for Four High-Brightness White LEDs2003 by Catalyst Semiconductor, Inc. Characteristics subject to change without notice Part Number CAT37EKK CAT37EKK-TE7 Package SOT23 (1mm height) SOT23 (1mm height) Tape & Reel 8-pad TDFN (3x4.9mm, MSOP Footprint) Tape & Reel 8-pad TDFN (3x3mm) Tape & Reel Tube Quantity Reel Quantity 3000 Package Marking Code BF Temperature Range 85� C (Top View) TDFN Package: 4.9mm 0.8mm maximum height (RD2)(Top View) TDFN Package: 3mm 0.8mm maximum height (RD4) Pin Number SOT23 1 Pin Number TDFN 8 Name SW Function Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area connected to this pin. Ground pin. Connect pin 2 to ground. LED (cathode) connection pin. Shutdown pin. Input supply pin. This pin should be bypassed with a capacitor to ground. A 1�F capacitor mounted close to the pin is recommended. Power Ground VIN , FB, SHDN Voltage......................................... V SW Voltage.......................................................... 20 V Junction Temperature....................................... 125�C Storage Temperature.......................... to 160�C ESD Rating - Human Body Model.................... 2000V Lead Soldering Temperature............................ 300�C Parameter VIN Ambient Temperature Range Inductor L1 Input Capacitor C1 Output Capacitor C2 ILED with to 4 LEDs in series Range 6.8 �20% typical 1.0 �20% typical 1.0 �20% typical to 20 Unit �F mA Over recommended operating conditions unless otherwise specified. = 25�C, VIN = 3V and VSHDN = 3V.Symbol Parameter Input Voltage Range IQ ISD VFB IFB Quiescent Current Shutdown Current FB Pin Voltage FB Pin Leakage Current Shutdown High Threshold Shutdown Low Threshold ISHDN fSW DC Shutdown Pin Current Boost Converter Frequency Maximum Switch Duty Cycle ISWL Switch Current Limit Switch Saturation Voltage Switch Leakage Current Efficiency ISW 300 mA Switch Off, VSW 5 V Figure 1 with specified components mV �A VRSET 0.2 V VSHDN LEDs mA 85 Conditions Min Typ Max Units V nA MHz % |
