PRELIMINARY TF4602 1.3 MHz Asynchronous Step-up Regulator White LED Driver Features Description Drives white LED arrays, up to 13x3 in size, for display backlighting Wide input voltage range: 2.5V to 6V High efficiency enabled by an integrated 500 mW power MOSFET switch Low 104 mV internal reference voltage brings additional power savings Operates at fixed 1.3 MHz frequency for small filter size 0.1 mA typical shut-down supply current Integrated soft-start function, 28V over-voltage protection, over-temperature protection and input under-voltage lockout Industrial temperature range: -40 °C to +85 °C Available in space saving QFN-8 and TSOT23-6 packages The TF4602 is a monolithic asynchronous boost regulator. An integrated 500 mW Power MOSFET drives up to 13 parallel strings of 3 WLEDs. It operates at fixed 1.3 MHz switching frequency, maximizing conversion efficiency, enabling smaller external components and reducing output ripple. Combined with a wide input voltage range of 2.5V to 6V the TF4602 is an ideal solution for portable electronic devices. Applications Ordering Information Cellular Phones Digital Cameras PDAs, Smart Phones, MP3 Players, OLEDs Portable Instruments Typical Application December 22, 2010 The TF4602 features an integrated soft-start function that minimizes inrush current during turn-on. Under-voltage lockout, over-voltage and over-temperature protection features are added for system robustness. It is available with an internal low voltage references of 104 mV for high efficiency. The current mode control loop is compensated internally minimizing the number of external components. The TF4602 is offered in space saving 8-pin QFN and 6-pin TSOT23 packages. It operates over the industrial temperature range of -40 °C to +85 °C temperature range. PART NUMBER VFB VOV PACKAGE TF4602-UT_ 104 mV 28V TSOT23-6 TF4602-NB_ 104 mV 28V QFN-8 NOTE1 For 180 mm reel insert suffix “P”; for 330 mm reel insert suffix “Q”. PRELIMINARY 1 TF4602 Pin Diagrams Top View: QFN-8 Top View: TSOT23-6 Functional Block Diagram Pin Descriptions PIN NAME SOT PIN NUMBER QFN PIN NUMBER PIN DESCRIPTION SW 1 8 GND 2 1, 5, 9 FB 3 6 Feedback input pin. The TF4602 regulates the voltage across the current sense resistor placed between the FB and GND pins. Connect the bottom of the LED string to the FB pin. The drain of the internal power MOSFET switch. Connect the power inductor and output rectifier to this pin. Ground pin. EN 4 4 Enable input pin. The EN pin is a digital input pin that enables or disables the regulator. When the EN is logic high, the regulator is turned ON. When the EN is logic low, the regulator is shut down. DO NOT leave the EN pin floating. OV 5 3 Output over-voltage monitor pin. Connect the OV pin to the output at the top of the LED string. VIN 6 2 Power input pin. The IN pin supplies the power to the IC and the stepup converter switch. NC - 7 “No Connect” pin. December 22, 2010 PRELIMINARY 2 TF4602 Absolute Maximum Ratings (NOTE2) VIN - Supply input pin voltage ......................................-0.3V to +6.5V VSW - Switching pin voltage .........................................-0.5V to +28.5V VOV - Over-voltage monitor pin voltage ...................-0.5V to +28.5V All other pins .....................................................................-0.3V to +6.5V TJ - Junction operating temperature .......................................+150 °C TL - Lead temperature (soldering, 10s) .................................. +260 °C Tstg - Storage temperature range ............................-65 °C to +150 °C QFN-8 Thermal Resistance (NOTE3) QJC...................................................................................................16 °C/W QJA..................................................................................................80 °C/W ESD Susceptibility HBM (NOTE4).....................................................................................2.5 kV MM (NOTE5........................................................................................200V CDM (NOTE6).....................................................................................1.5 kV SOT-23-6 Thermal Resistance (NOTE3) QJC................................................................................................110 °C/W QJA...............................................................................................220 °C/W NOTE2 Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. NOTE3 When mounted on a standard JEDEC 2-layer FR-4 board. Recommended Operating Conditions VIN - Input voltage ...................................................................2.5V to 6V TA - Operating ambient temperature range..........-40 °C to +85 °C TJ - Junction temperature range..............................-40 °C to +125 °C NOTE4 Human Body Model, applicable standard JESD22-A114-C NOTE5 Machine Model, applicable standard JESD22-A115-A NOTE6 Field Induced Charge Device Model, applicable standard JESD22-C101-C Electrical Characteristics TA = 25 °C, VIN = 5V, unless otherwise specified. Symbol Parameter Conditions MIN VIN Input voltage VUVLO Under-voltage lockout VUVLOhyst UVLO hysteresis IQ Quiescent current VFB = 0.15V, Not Switching IIN Supply current VFB = 0V, Switching ISHDN Shut-down current VEN = 0V RDS(ON) Switch ON resistance VFB Feedback voltage IFB Feedback input bias current VFB = 0.1V Line regulation Load regulation TYP 2.5 VIN rising 2.25 MAX Unit 6.0 V 2.45 V 0.1 V 690 750 mA 1 2 mA 0.1 1 mA 0.5 1.0 W 94 104 114 mV -600 -300 nA VIN = 3V to 4.3V (NOTE7) 1 % IOUT = 1 mA to 180 mA (NOTE8) 1 % NOTE7 Line regulation is measured on the system illustrated in Figure 1 with the following component values and loading: CIN = 2.2 mF, COUT = 1 mF, IOUT = 180 mA, L = 10 mH. NOTE8 Load regulation is measured on the system illustrated in Figure 1 with the following component values: CIN = 2.2 mF, COUT = 1 mF, L = 10 mH. December 22, 2010 PRELIMINARY 3 TF4602 Symbol Parameter fosc Oscillator frequency DMAX Maximum duty cycle VIH Enable input logic high voltage VIL Enable input logic low voltage VEN Rising, VIN = 5V 1.0 VEN Rising, VIN = 2.5V 0.8 IIN Enable input current VEN = 0V, 5V VENhyst Enable input threshold voltage hysteresis VOVP Output over-voltage threshold VOVP rising 26 28 IOCP Over-current threshold 60% duty cycle 1 1.33 A TOTP Over-temperature threshold 160 °C TOTPhyst Over-temperature threshold hysteresis 30 °C December 22, 2010 Conditions MIN TYP MAX Unit 1.0 1.3 1.5 MHz VFB = 0V 85 92 VEN Rising, VIN = 5V 1.6 % V 1 90 PRELIMINARY V mA mV 30 V 4 TF4602 Application Information The TF4602 is a monolithic asynchronous boost regulator featuring an integrated 500 mW Power MOSFET that can drive up to 39 white LEDs configured in a 3x13 array. It operates over a wide 2.5V to 6V input voltage range while providing under-voltage, over-voltage and over-temperature protection. This section of the datasheet describes typical application circuits, provides recommendations on dimming control and component selection, and discusses thermal and layout design considerations. TYPICAL APPLICATIONS The TF4602 uses a fixed frequency, current-mode step-up regulator architecture to drive arrays of white LEDs. Figure 1 shows a typical application circuit. Figure 2. Constant Output Voltage Boost Regulator Circuit SETTING THE LED CURRENT Based on the circuit of Figure 1, the LED current depends on the reference voltage, VREF, and the resistor, RSET, as expressed with the following equation: ILED = Table 1 exemplifies several standard resistor values needed for a given LED current. If standard resistor values are not available a parallel combination of two standard resistors may also be used to get the desired LED current. Figure 1. Typical Application Circuit The circuit of Figure 1 can drive various topologies of white LEDs ranging from 3x1 arrays to 3x13 arrays. The component selection may vary for each topology depending on the VOUT / VIN ratio and the LED current requirements. This is discussed in the later subsections of the Application Information. VREF [mV] 104 The TF4602 can also be used as a constant output voltage boost regulator as shown in Figure 2. The constant output voltage can be determined using the following equation: VOUT = VREF December 22, 2010 RL + RSET [V ]; RSET > 10kΩ RSET VREF RSET ILED [mA] RSET [W] 10 10.5 20 5.23 100 1.05 180 1.2 || 1.1 260 0.4 Table 1. Examples of Standard Value Resistors for a Given LED Current PRELIMINARY 5 TF4602 COMPONENT SELECTION Inductor: High frequency operation of the TF4602 allows the use of small surface mount inductors. The minimum inductance value is inversely proportional to the operating frequency and is bounded by the following limits: Vripple ( BULK ) = IL( peak ) VIN COUT VOUT f [V ] where V (V − VIN ( MIN ) ) 3 L > [mH ] ∧ L > IN ( MIN ) OUT ( MAX ) [H ] f f IL( MAX )ripple VOUT ( MAX ) where • f = Operating frequency [Hz] • IL(MAX)ripple = Allowable maximum inductor current ripple [A] • VIN(MIN) = Minimum input voltage [V] • VOUT(MAX) = Maximum output voltage [V] • f = Operating frequency [Hz] • IL(peak) = Peak inductor current [A] • VIN(MIN) = Input voltage [V] • VOUT(MAX) = Output voltage [V] Another significant component of the output voltage ripple is the ripple due to the capacitor ESR. This components is simply expressed in the following equation: The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. Given this, the operating frequency and the input and output voltage ranges for the TF4602 regulator circuits, it is easy to calculate the optimal inductor value which typically ranges between 10 and 47 mH. For high efficiency, it is recommended to select an inductor with a high frequency core material (e.g. ferrite) to minimize core losses. Low ESR (equivalent series resistance) is another preferred inductor characteristic when designing for low losses. The inductor must handle the peak inductor current at full load without saturating. Chip inductors typically do not have enough core to support the peak inductor currents above 1A and are not suitable for the TF4602 applications. Lastly, select a toroid, pot core or shielded bobbin inductor for low radiated noise. Table 2 provides a list of recommended inductor series. Inductor Series Supplier Website SRU8043 Bourns Inc. www.bourns.com MSS7341 Coilcraft www.coilcraft.com LQH88P Murata www.murata.com DR1040 Coiltronics www.coiltronics.com CDRH8D43 Sumida www.sumida.com Table 2. List of Recommended Inductor Series Input Capacitor: The input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. The input capacitor values in the range between 2.2 and 4.7 mF are sufficient in most cases. Ceramic, low ESR capacitors are recommended for a low loss operation. December 22, 2010 Output Capacitor: The value of the output capacitor has an effect on the output voltage ripple as expressed in the following equation: Vripple ( ESR ) = IL( peak ) ESRCOUT [V ] The output capacitor values in the range between 1.0 and 2.2 mF provide low output voltage ripple in most cases. Table 3 provides a list of recommended capacitor series. Capacitor Series Supplier Website 0201-2225 Ceramic TPS, TPM Tantalum AVX www.avx.com MK107, MK212, MK316 Ceramic Taiyo Yuden www.t-yuden.com POSCAP Electrolytic Sanyo edc.sanyo.com Table 3. List of Recommended Capacitor Series Output Diode: The primary function of the output diode is to protect the TF4602 VIN pin when the output voltage is above the absolute maximum voltage rating of the pin (6.5V). Schottky diodes feature low forward voltage and fast recovery times that result in improved peak efficiency of the boost regulator circuits. Table 4 provides a list of recommended diode series. Diode Series Supplier Website MBR0520-80 MCC www.mccsemi.com SBR Diodes Inc. www.diodes.com SS1P3 Vishay www.vishay.com Table 4. List of Recommended Schottky Diode Series PRELIMINARY 6 TF4602 DIMMING CONTROL There are three popular methods to control dimming for the TF4602 white LED driver circuits. The details of each method follow. Using a DC Voltage: Dimming control using a variable DC voltage is shown in Figure 3. Figure 4. Dimming Control Using a Filtered PWM Signal Figure 3. Dimming Control Using a Variable DC Voltage As the DC voltage increases, the current through the R1 increases. The higher the IR1, the lower the ILED as the control loop is now regulating the sum of the IR1 and ILED. The ILED can be calculated using the following equation: VREF − ILED = The PWM signal in the circuit of Figure 4 affects the output voltage ripple. To minimize this effect, recommended frequency of the signal is 1 kHz or greater. Using a PWM Logic Signal: Dimming control using a PWM logic signal is shown in Figure 5. R1 (VDC − VREF ) R2 [ A] RSET As an example, if the VDC is varied between 0V and 2.0V, the selection of R1 =5 kW, R2 = 90 kW and RSET = 5.23W sets the ILED between approximately 21 mA and 0 mA for the TF4602 (VREF = 104 mV). Using a Filtered PWM Signal: Dimming control using a filtered PWM signal is another popular method for LED dimming control and is show in Figure 4. In this method, a filtered PWM signal acts as the DC voltage to regulate the output current. The ILED can be calculated using the following equation: VREF − ILED = December 22, 2010 R1 (VPWM DCD − VREF ) R2 + R3 [ A] RSET Figure 5. Dimming Control Using a PWM Logic Signal The PWM logic signal is applied to the EN pin of the TF4602. The average ILED is directly proportional to the DCD of the PWM logic signal. The frequency of the signal should be 1 kHz or lower due to the soft-start function. PRELIMINARY 7 TF4602 Package Dimensions (TSOT23-6) December 22, 2010 PRELIMINARY 8 TF4602 Package Dimensions (QFN-8) December 22, 2010 PRELIMINARY 9 TF4602 Notes Important Notice Telefunken Semiconductors does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Telefunken Semiconductors reserves the right to change said circuitry and specifications at any time without notice. If Military/Aerospace or Automotive specified devices are required, please contact the Telefunken Semiconductors Sales Office or Distributors for availability and specifications. LIFE SUPPORT POLICY TELEFUNKEN SEMICONDUCTORS’ PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE CEO OF TELEFUNKEN SEMICONDUCTORS. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. December 22, 2010 PRELIMINARY 10