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| HT7939 High Current and Performance White LED Driver Features * Input range from 2.6V~5.5V * Built-in Power MOSFET * Can drive up to 39 White LEDs with a 5V input * Low standby current: 0.1mA (typ.) with VEN low * Integrated Over-voltage, Over-temperature and * Under voltage lock-out protection * 1.2MHz fixed switching frequency * High efficiency - up to 90% * 6-pin SOT23-6 package Over-current protection circuits Applications * Display Backlighting * LED lighting Automatic DVD player Digital photo frame Handheld computer General Description The HT7939 is a high efficiency boost converter for driving White LEDs using current mode operation. The device is designed to drive up to 39 White LEDs from a 5V power supply. The White LED current is setup using an external current setting resistor, which has a low feedback voltage of 0.2V to minimise power losses in the resistor which improves efficiency. The Over-voltage function prevents damage to the IC by turning off the converter when the LED load is open circuit. The device includes over current protection, over temperature protection and under voltage protection preventing damage to the device when the output is overloaded. Rev 1.10 1 November 3, 2009 HT7939 Block Diagram 32V Pin Assignment S O T 2 3 -6 V IN 6 OVP 5 EN 4 T o p V ie w 1 SW 2 GND 3 FB Pin Description Pin No. 1 2 Pin Name SW GND Description Switching pin. Internal power MOSFET drain. Connected to inductor and diode. Signal Ground. Feedback pin. Reference voltage. The HT7939 feedback voltage is 200mV. Connect the sense resistor from FB to GND to set the LED current. Calculate resistor value according to 200mV . RFB = ILED Shutdown & Dimming control input. Dont allow this pin to float. Over voltage protection pin which is connected to the output. Input supply pin. The input supply pin for the IC. Connect VIN to a supply voltage between 2.6V~5.5V. 3 FB 4 5 6 EN OVP VIN Rev 1.10 2 November 3, 2009 HT7939 Absolute Maximum Ratings Input Voltage...........................................................6.0V FB Voltage ..............................................................6.0V OVP Voltage ............................................................38V Storage Temperature Range ..............-55C to +150C SW Voltage..............................................................38V EN ..........................................................................6.0V Operating Temperature Range .............-40C to +85C Maximum Junction Temperature........................+150C Note: These are stress ratings only. Stresses exceeding the range specified under Absolute Maximum Ratings may cause substantial damage to the device. Functional operation of this device at other conditions beyond those listed in the specification is not implied and prolonged exposure to extreme conditions may affect device reliability. Electrical Characteristics Symbol VIN UVLO IIN Parameter Input Voltage Under Voltage Lockout Supply Current VEN= 0V 3/4 3/4 Switching VIN=5V; L=10mH; Ta=25C (Unless otherwise specified) Test Conditions Min. 2.6 3/4 3/4 3/4 Typ. 3/4 2.4 1.0 0.1 Max. 5.5 2.5 2.5 1.0 Unit V V mA mA Error Amplifier VFB Feedback Voltage 3/4 190 200 210 mV Power Switch fOSC DC RDS(ON) ISW(OFF) EN Pin VIH VIL EN Voltage High EN Voltage Low VIN=2.6V~5.5V VIN=2.6V~5.5V 2.0 3/4 3/4 3/4 3/4 0.8 V V Switching Frequency Measurement at SW pin Maximum Duty Cycle SW On Resistance Switch Leakage Current 3/4 3/4 85 3/4 3/4 90 0.5 0.1 0.8 1.2 1.6 3/4 3/4 1.0 MHz % W mA OVP and OCP VOVP IOCP OVP Threshold N-channel MOSFET Current Limit No load 3/4 29 3/4 32 950 35 3/4 V mA Thermal Shutdown TSHUT Thermal Shutdown Threshold Thermal shutdown Hysteresis 3/4 3/4 3/4 3/4 150 15 3/4 3/4 C C Rev 1.10 3 November 3, 2009 HT7939 Function Description VIN Under-Voltage Lockout - UVLO The device contains an Input Under Voltage Lockout (UVLO) circuit. The purpose of the UVLO circuit is to ensure that the input voltage is high enough for reliable operation. When the input voltage falls below the under voltage threshold, the internal FET switch is turned off. If the input voltage rises by the under voltage lockout hysteresis, the device will restart. The UVLO threshold is set below the minimum input voltage of 2.6V to avoid any transient VIN drops under the UVLO threshold and causing the converter to turn off. Current Limit Protection The device has a cycle-by-cycle current limit to protect the internal power MOSFET. If the inductor current reaches the current limit threshold, the MOSFET will be turned off. It is import to note that this current limit will not protect the output from excessive current during an output short circuit. If an output short circuit has occurred, excessive current can damage both the inductor and diode. Over-Voltage Protection - OVP The device provides an over-voltage protection function. If the FB pin is shorted to ground or an LED is disconnected from the circuit, the FB pin voltage will fall to zero and the internal power MOSFET will switch with its full duty cycle. This may cause the output voltage to exceed its maximum voltage rating, possibly damaging the IC and external components. Internal over-voltage protection circuitry turns off the power MOSFET and shuts down the IC as soon as the output voltage exceeds the VOVP threshold. As a result, the output voltage falls to the level of the input supply voltage. The device remains in shutdown mode until the power is recycled. Over-Temperature protection - OTP A thermal shutdown is implemented to prevent damages due to excessive heat and power dissipation. Typically the thermal shutdown threshold is 150C. When the thermal shutdown is triggered the device stops switching until the temperature falls below typically 135C. Then the device starts switching again. Application Information * Inductor Selection I IN (M A X ) Choose an inductor that can handle the necessary peak current without saturating, and ensure that the inductor has a low DCR to minimise power losses. A 10mH~22mH inductor should be a good choice for most HT7939 applications. However, a more exact inductance value can be calculated. A good rule for choosing an inductor value is to allow the peak-to-peak ripple current to be approximately 30~50% of the maximum input current. Calculate the required inductance value using the following equation: L= V = V IN (V F OUT OUT SW -V IN ) L OUT DI V I V IN O U T (M A X ) h IN (M A X ) DI L = (3 0 % =I ~ 50% )I IN (M A X ) I L (P E A K ) + 1 2 D IL In the equation above, IOUT(MAX) is the maximum load current, DIL is the peak-to-peak inductor ripple current, h is the converter efficiency, FSW is the switching frequency and IL(PEAK) is the peak inductor current. * Output Capacitor Selection The output capacitor determines the steady state output voltage ripple. The voltage ripple is related to the capacitors capacitance and its ESR (Equivalent Series Resistance). A ceramic capacitor with a low ESR value will provide the lowest voltage ripple and are therefore recommended. Due to its low ESR, the capacitance value can be calculated by the equation: C out = V (V O -V F IN SW ) IO UT r ip p le OUT V In the equation above, Vripple =peak to peak output ripple, FSW is the switching frequency. A 1mF~10mF ceramic capacitor is suitable for most application. * Input Capacitor Selection The selection of the inductor affects steady state operation as well as transient behavior and loop stability. There are three important electrical parameters which need to be considered when choosing an inductor: the value of inductor, DCR (copper wire resistance) and the saturation current. An input capacitor is required to supply the ripple current to the inductor, while limiting noise at the input source. A low ESR ceramic capacitors is required to keep the noise at the IC to a minimum. A 4.7mF~10mF ceramic capacitor is suitable for most application. This capacitor must be connected very close to the VIN pin and inductor, with short traces for good noise performance. Rev 1.10 4 November 3, 2009 HT7939 * Schottky Diode Selection Layout Considerations Circuit board layout is a very important consideration for switching regulators if they are to function properly. Poor circuit layout may result in related noise problems. In order to minimize EMI and switching noise, please follow the guidelines below: * All tracks should be as wide as possible. * The input and output capacitors, C1 and C2, should The output rectifier diode conducts during the internal MOSFET is turn off. The average and peak current rating must be greater than the maximum output current and peak inductor current. The reverse breakdown voltage must be greater than the maximum output voltage. It is recommended to use a schottky diode with low forward voltage to minimize the power dissipation and therefore to maximize the efficiency of the converter. A 1N5819 type diode is recommended for HT7939 applications. * LED Current Selection be placed close to the VIN, VO and GND pins. * The Schottky diode, D1, and inductor, L, must be placed close to the SW pin. * Feedback resistor, Rfb, must be placed close to the The LED current is controlled by the current sense feedback resistor Rfb, The current sense feedback reference voltage is 200mV. In order to have accurate LED currents, precision resistors are the preferred type with a 1% tolerance. The LED current can be calculated from the following formula. I LED FB and GND pins. * A full ground plane is always helpful for better EMI performance. A recommended PCB layout with component locations is shown below. = V R FB fb = 200m V R fb Where ILED is the total output LED current, VFB=feedback voltage, Rfb=current sense resistor. * Digital and Analog Dimming Control The LED illumination level can be controlled using both digital and analog methods. The digital method uses a PWM signal applied to the EN pin. This is shown in figure 14. The average LED current increases proportionally with the PWM signal duty cycle. A 0% duty cycle corresponds to zero LED current. A 100% duty cycle corresponds to full LED current. The PWM signal frequency should be set below 1kHz due to the delay time of device startup. There are two methods of analog LED brightness control. The first method uses a DC voltage to control the feedback voltage. If the DC voltage range is from 0V to 3.3V, the selection of resistors control the LED current from 20mA to 0mA as shown in figure15. The other way is to use a filtered PWM signal, as shown in figure16. The filtered PWM signal application acts in the same way as the DC voltage dimming control. Top Layer Bottom Layer Rev 1.10 5 November 3, 2009 HT7939 Typical Performance Characteristics Fig.1 Efficiency vs Input Voltage Fig.5 Enable Voltage VS Input Voltage Fig.6 Feedback Voltage VS Input Voltage Fig.2 LED Current VS PWM Dimming (3S10P LEDs) Fig.3 Switching frequency VS Input Voltage Fig.7 RDS(ON) VS Temperature Fig.4 Supply Current VS Input Voltage Rev 1.10 6 November 3, 2009 HT7939 Fig.8 Switching Waveform Fig.11 200Hz PWM Dimming Waveform Fig.9 Start-up Waveform Fig. 12 1kHz PWM Dimming Waveform Fig.10 Open LED Protection Rev 1.10 7 November 3, 2009 HT7939 Application Circuits V IN 4 .5 V ~ 5 .5 V 4 .7 m F 10mH 1N5819 2 .2 m F V IN EN SW OVP FB R fb 0 .7 7 W 1 3 S tr in g s GND H T7939 L : G S 5 4 -1 0 0 K (G A N G S O N G ) C 1 : G R M 2 1 B R 6 1 E 4 7 5 K A 1 2 L (M U R A T A ) C 2 : G R M 2 1 B R 7 1 E 2 2 5 K A 7 3 L (M U R A T A ) Figure 13. Application Circuits for Driving 39 WLEDs V IN 4 .5 V ~ 5 .5 V 4 .7 m F 10mH 1N5819 2 .2 m F V IN EN SW OVP FB 1 3 S tr in g s PW M S ig n a l GND H T7939 R fb 0 .7 7 W Figure 14. Application Circuit for Dimming Control Using a PWM Logic Signal V IN 4 .5 V ~ 5 .5 V 4 .7 m F 10mH 1N5819 2 .2 m F V IN EN SW OVP FB 150kW 10kW 1 3 S tr in g s GND H T7939 R fb 0 .7 7 W V D C D im m in g 0 V ~ 3 .3 V Figure 15. Application Circuit for Dimming Control Using a DC Voltage Rev 1.10 8 November 3, 2009 HT7939 V IN 4 .5 V ~ 5 .5 V 4 .7 m F 10mH 1N5819 2 .2 m F V IN EN SW OVP FB 10kW 1 3 S tr in g s GND H T7939 3 .3 V 0V PW M 150kW 10kW S ig n a l 0 .1 m F R fb 0 .7 7 W Figure 16. Application Circuit for Dimming Control Using a Filtered PWM Signal V IN 5 .0 V 4 .7 m F 10mH 1N5819 2 .2 m F V IN EN SW 350m A OVP FB R fb 0 .5 7 W GND H T7939 Figure 17. Application Circuit for Drive 3 High Brightness LEDs Rev 1.10 9 November 3, 2009 HT7939 Package Information 6-pin SOT23-6 Outline Dimensions D C L E H e A2 b A1 A Symbol A A1 A2 b C D E e H L q Dimensions in mm Min. 1.0 3/4 0.7 0.35 0.10 2.7 1.4 3/4 2.6 0.37 1 Nom. 3/4 3/4 3/4 3/4 3/4 3/4 3/4 1.9 3/4 3/4 3/4 Max. 1.3 0.1 0.9 0.50 0.25 3.1 1.8 3/4 3.0 3/4 9 Rev 1.10 10 q November 3, 2009 HT7939 Product Tape and Reel Specifications Reel Dimensions T2 D A B C T1 SOT23-6 Symbol A B C D T1 T2 Description Reel Outer Diameter Reel Inner Diameter Spindle Hole Diameter Key Slit Width Space Between Flange Reel Thickness Dimensions in mm 178.01.0 62.01.0 13.00.2 2.500.25 8.4 11.4 +1.5/-0.0 +1.5/-0.0 Rev 1.10 11 November 3, 2009 HT7939 Carrier Tape Dimensions D E F P0 P1 t W C B0 D1 P A0 K0 R e e l H o le IC p a c k a g e p in 1 a n d th e r e e l h o le s a r e lo c a te d o n th e s a m e s id e . SOT23-6 Symbol W P E F D D1 P0 P1 A0 B0 K0 t C Description Carrier Tape Width Cavity Pitch Perforation Position Cavity to Perforation (Width Direction) Perforation Diameter Cavity Hole Diameter Perforation Pitch Cavity to Perforation (Length Direction) Cavity Length Cavity Width Cavity Depth Carrier Tape Thickness Cover Tape Width Dimensions in mm 8.00.3 4.00.1 1.750.1 3.500.05 1.5 1.5 +0.1/-0.0 +0.1/-0.0 4.00.1 2.000.05 3.150.10 3.20.1 1.40.1 0.200.03 5.30.1 Rev 1.10 12 November 3, 2009 HT7939 Holtek Semiconductor Inc. (Headquarters) No.3, Creation Rd. II, Science Park, Hsinchu, Taiwan Tel: 886-3-563-1999 Fax: 886-3-563-1189 http://www.holtek.com.tw Holtek Semiconductor Inc. (Taipei Sales Office) 4F-2, No. 3-2, YuanQu St., Nankang Software Park, Taipei 115, Taiwan Tel: 886-2-2655-7070 Fax: 886-2-2655-7373 Fax: 886-2-2655-7383 (International sales hotline) Holtek Semiconductor Inc. (Shenzhen Sales Office) 5F, Unit A, Productivity Building, No.5 Gaoxin M 2nd Road, Nanshan District, Shenzhen, China 518057 Tel: 86-755-8616-9908, 86-755-8616-9308 Fax: 86-755-8616-9722 Holtek Semiconductor (USA), Inc. (North America Sales Office) 46729 Fremont Blvd., Fremont, CA 94538, USA Tel: 1-510-252-9880 Fax: 1-510-252-9885 http://www.holtek.com Copyright O 2009 by HOLTEK SEMICONDUCTOR INC. The information appearing in this Data Sheet is believed to be accurate at the time of publication. However, Holtek assumes no responsibility arising from the use of the specifications described. The applications mentioned herein are used solely for the purpose of illustration and Holtek makes no warranty or representation that such applications will be suitable without further modification, nor recommends the use of its products for application that may present a risk to human life due to malfunction or otherwise. Holteks products are not authorized for use as critical components in life support devices or systems. Holtek reserves the right to alter its products without prior notification. For the most up-to-date information, please visit our web site at http://www.holtek.com.tw. Rev 1.10 13 November 3, 2009 |
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