HT7939A High Current and Performance White LED Driver Feature General Description • Input voltage range: 2.6V~5.5V The HT7939A is a high efficiency boost converter for driving multiple 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 resistor power losses and thus improving efficiency. • High efficiency - up to 90% • Integrated N-ch MOSFET • Can drive up to 39 WLEDs from a 5V input • Low standby current: 0.1mA (typ.) • Built-in OVP, OCP, OTP, UVLO protection • EN pin dimming frequency up to 200kHz The HT7939A has a dimming frequency of up to 200kHz, which has excellent linear performance over this dimming frequency range. The over voltage function prevents device damage by turning off the converter should the LED load become open circuit. The device also includes over current protection, over temperature protection and under voltage protection preventing damage to the device should the output be overloaded. • 1.2MHz fixed switching frequency • SOT23-6 package Applications • Display backlighting –– Automatic –– DVD player –– Digital photo frame –– Handheld computer Selection Guide Part No. Package Marking HT7939A SOT23-6 39A-1 (OVP=17.6V) 39A-2 (OVP=32.0V) Note: Both lead free and green compound devices are available. Rev. 1.20 1 November 04, 2013 HT7939A Block Diagram Pin Assignment V IN 6 O V P 5 E N 4 3 9 A -3 1 2 3 S W G N D F B T o p V ie w Pin Descriptin PIN No. PIN Name 1 SW 2 GND 3 FB Feedback pin. Reference voltage. The HT7939A feedback voltage is 0.2V. 4 EN Shutdown & Dimming control input. Do not allow this pin to float. 5 OVP Over voltage protection pin which is connected to the output. 6 VIN The input supply pin for the IC. Connect VIN to a supply voltage between 2.6V~5.5V. Rev. 1.20 Description Switching pin. Connected to inductor and diode. Ground. 2 November 04, 2013 HT7939A Absolute Maximum Ratings Input Voltage, FB Voltage, EN . ........................... 6.0V Operating Temperature Range ........... -40°C to +85°C SW Voltage ........................................................... 36V Storage Temperature Range ............. -55°C to +150°C OVP Voltage ......................................................... 36V Maximum Junction Temperature ...................... 150°C 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 VIN= 5.0V, Ta= 25°C, unless otherwise specified (note 1) Symbol Parameter Test Conditions Min. Typ. Max. Unit Input Supply Voltage and Current VIN Input Voltage ― 2.6 ― 5.5 V UVLO Under Voltage Lockout ― 1.8 2.1 2.4 V IIN Supply Current Switching ― 1.0 5.0 mA VEN= 0 ― 0.1 1.0 μA ― 190 200 210 mV VIN= 3.0V~4.3V, ILED= 20mA ― 1.0 ― % 0.8 1.2 1.6 MHz 85 90 ― % Error Amplifier VFB Feedback Voltage V Line Regulation Power Switch fOSC Switching Frequency DC Maximum Duty Cycle RDS(ON) SW ON Resistance ― ― 0.5 ― Ω ISW(OFF) Switch Leakage Current ― ― 0.1 1.0 μA VIH EN Voltage High ― 2.0 ― ― V VIL EN Voltage Low ― ― ― 0.8 V fEN Dimming Clock Rate Duty= 5%~100% 100 ― 200 kHz No Load, for 39A-1 Marking 15.8 17.6 19.4 V Measured at SW Pin Enable OVP and OCP VOVP OVP Threshold IOCP N-channel MOSFET Current limit No Load, for 39A-2 Marking 28.8 32.0 35.2 V ― 1000 1200 ― mA Thermal Shutdown Threshold ― ― 150 ― °C Thermal Shutdown Hysteresis ― ― 25 ― °C Thermal Shutdown tSHUT Note 1. Specifications are production tested at Ta=25 degree. Specifications over -40°C to 85°C degree operating temperature range are assured by design, characterization. Rev. 1.20 3 November 04, 2013 HT7939A Functional Description Application Information VIN Under-Voltage Lockout -- UVLO Inductor Selection The HT7939A 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 is below the UVLO threshold, the internal power MOSFET will remain switched off .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. There are three important electrical parameters that need to be considered when choosing an inductor. These are the inductor value, the DCR (parasitic serial DC resistance) and the saturation current. The inductor’s value determines the input ripple current. Lower inductor values decrease the physical size of the inductor, but increase the input ripple current. However, larger inductor values decrease the input ripple current, but have higher series resistances and lower saturation currents. A good rule to choose a sutiable inductor value is to allow the peak-topeak ripple current to be approximately 30~50% of the maximum input current. Calculate the required inductance value using the following equations: Current Limit Protection The HT7939A 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 important to note that this current limit will not protect the output from excessive current during an output short circuit. If an output short circuit occurs, excessive current can damage both the inductor and the diode. Over-Voltage Protection -- OVP The HT7939A provides an over-voltage function. If the FB pin is shorted to ground or an LED is disconnected from the circuit, the FB pin voltage will be zero and the internal power MOSFET will switch at its fully duty cycle. This may cause the output voltage to exceed its maximum voltage rating, possibly damaging the device and the external components. Internal over voltage protection circuitry turns off the power MOSFET and shuts down the device as soon as the output voltage exceeds the threshold .As a result, the output voltage falls to the level of the input supply voltage. The device remains in this shutdown mode until it is enabled once again to a reset condition by the EN pin or after the power is restarted. In the equations above, I OUT(MAX) is the maximum load current, ∆IL is the peak-to-peak inductor ripple current, η is the converter efficiency, F SW is the switching frequency and IL(PEAK) is the peak inductor current. To prevent inductor core saturation, ensure that the inductor-saturation current is rated higher than the peak inductor current. A 10µH inductor value is recommended for most HT7939A applications. Over-Temperature protection -- OTP A thermal shutdown function is implemented to prevent device damage due to excessive heat and power dissipation. Typically the thermal shutdown threshold is 150 °C . When the thermal shutdown is triggered the device stops switching until the temperature falls below a typical value of 125°C. After this the device will once again resume switching. Rev. 1.20 4 November 04, 2013 HT7939A Input and Output Capacitor Selection LED Current Selection The output capacitor determines the steady state output voltage ripple. The voltage ripple is related to the capacitor’s capacitance and its ESR which is the Equivalent Series Resistance. Ceramic capacitors with low ESR values will result in the lowest ripple voltage values and are the recommended type. Due to their low ESR values, the capacitance value can be calculated using the following equation: The LED current is controlled by the current sense feedback resistor R fb, The current sense feedback reference is 200mV. In order to ensure accurate LED currents, precision resistors with a 1% tolerance are the preferred types. The LED current can be calculated using the following formula: Where ILED is the output LED current, VFB=feedback voltage, Rfb=current sense resistor. In the equation above, Vripple= peak to peak output ripple, FSW is the switching frequency. Digital and Analog Dimming Control The Digital dimming method uses a PWM signal applied to the EN pin and the EN Pin dimming frequency up to 200kHz. This is shown in fig.19. 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 a full LED current. The output capacitor is recommended to be in a range of 1μF to 10μF. The input capacitor is required to be in a range of 2.2μF to 10.0μF. The output capacitor affects the loop stability of the boost regulator. If the output capacitor is lower than this range, the boost regulator could potentially become unstable. There are two methods to control the LED brightness for analog dimming. 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 provided in fig.20 controls the LED current from 20mA to 0mA. Other applications a filtered PWM signal, which is shown in fig.21. The filtered PWM signal application acts the same way as the DC voltage dimming control. Schottky Diode Selection The output rectifier diode supplies current to the inductor when the internal MOSFET is off. The average and peak current ratings of the diode 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 a low forward voltage to minimise power dissipation and therefore to maximise the efficiency of the converter. A 1N5819 diode type is recommended for HT7939A applications. Rev. 1.20 5 November 04, 2013 HT7939A Typical Performance Characteristics Fig.4 Efficiency V.S. Input Voltage Fig.1 HT7939A-1 W-LED Current V.S. Dimming (3S13P) Fig.5 Feedback Voltage V.S. Input Voltage Fig.2 HT7939A-1 W-LED Current V.S. Dimming (3S10P) Fig.6 HT7939A-1 3S10P Dimming=100Hz, D=50%, Fig.3 HT7939A-2 W-LED Current V.S. Dimming (7S4P) VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=VEN Signal, CH2=ILED Current) Rev. 1.20 6 November 04, 2013 HT7939A Fig.7 HT7939A-1 3S10P Dimming=10kHz, D=50% , Fig.10 HT7939A-1 3S10P OVP Waveform VIN=5.0V VIN = 5.0V, L=22mH, VIN=COUT=2.2mF L=22mH, CIN=COUT=2.2mF (CH1=VEN Signal, CH2=ILED Current) (CH1=Switching Signal, CH2=VOUT) Fig.8 HT7939A-1 3S10P Dimming=200kHz, D=50%, Fig.11 HT7939A-1 3S10P Basic Waveform, VIN=5.0V, L=22mH, CIN=COUT=2.2mF VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=VEN Signal CH2=ILED Current) (CH1=Switching Signal, CH2=Inductor Current) Fig.9 HT7939A-1 3S10P Start Up Waveform Fig.12 HT7939A-2 7S4P Dimming=100Hz, D=50% VIN=5.0V, L=22mH, CIN=COUT=2.2mF VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=CIN, CH2= VOUT) Rev. 1.20 (CH1=VEN Signal, CH2=ILED Current) 7 November 04, 2013 HT7939A Fig.13 HT7939A-2 7S4P Dimming=10kHz, D=50% Fig.16 HT7939A-2 7S4P OVP Waveform, VIN=5.0V, L=22mH, CIN=COUT=2.2mF VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=VEN Signal, CH2=ILED Current) (CH1= Switching Signal, CH2= VOUT) Fig.14 HT7939A-2 7S4P Dimming=200kHz, D=50%, Fig.17 HT7939A-2 7S4P basic waveform, VIN=5.0V, L=22mH, CIN=COUT=2.2mF VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=VEN Signal, CH2=ILED Current) Fig.15 HT7939A-2 7S4P Start Up Waveform, VIN=5.0V, L=22mH, CIN=COUT=2.2mF (CH1=CIN, CH2= VOUT) Rev. 1.20 8 November 04, 2013 HT7939A Application Circuits L D1 10mH/22mH 1N5819 VIN C1 2.2mF VIN SW EN OVP GND FB VOUT C2 2.2mF 3S13P Rfb 1W HT7939A Fig.18 Application for Driving 3S13P WLEDs L D1 10mH/22mH 1N5819 VIN C1 2.2mF PWM Signal VIN SW EN OVP GND FB VOUT C2 2.2mF 3S13P Rfb 1W HT7939A Fig.19 Application for Dimming Control Using A PWM Signal L D1 10mH/22mH 1N5819 VIN C1 2.2mF VIN SW EN OVP GND FB VOUT C2 2.2mF 3S13P 10kW Rfb 1W 150kW HT7939A 0V~3.3V Fig.20 Application for Dimming Control Using a DC Voltage L D1 10mH/22mH 1N5819 VIN C1 2.2mF VIN SW EN OVP GND FB VOUT C2 2.2mF 3S13P 10kW 150kW HT7939A PWM Signal Rfb 1W 0.1mF Fig.21 Application for Dimming Control Using a Filtered PWM Signal Rev. 1.20 9 November 04, 2013 HT7939A Package Information Note that the package information provided here is for consultation purposes only. As this information may be updated at regular intervals users are reminded to consult the Holtek website for the latest version of the package information. Additional supplementary information with regard to packaging is listed below. Click on the relevant section to be transferred to the relevant website page. • Further Package Information (include Outline Dimensions, Product Tape and Reel Specifications) • Packing Meterials Information • Carton information • PB FREE Products • Green Packages Products Rev. 1.20 10 November 04, 2013 HT7939A 6-pin SOT23–6 Outline Dimensions Symbol Nom. Max. A ― ― 0.057 A1 ― ― 0.006 A2 0.035 0.045 0.051 b 0.012 ― 0.020 C 0.003 ― 0.009 D ― 0.114 BSC ― E ― 0.063 BSC ― e ― 0.037 BSC ― e1 ― 0.075 BSC ― H ― 0.110 BSC ― L1 ― 0.024 BSC ― θ 0° ― 8° Symbol Rev. 1.20 Dimensions in inch Min. Dimensions in mm Min. Nom. Max. A ― ― 1.45 A1 ― ― 0.15 A2 0.90 1.15 1.30 b 0.30 ― 0.50 C 0.08 ― 0.22 D ― 2.90 BSC ― E ― 1.60 BSC ― e ― 0.95 BSC ― e1 ― 1.90 BSC ― H ― 2.80 BSC ― L1 ― 0.60 BSC ― θ 0° ― 8° 11 November 04, 2013 HT7939A Copyright© 2013 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. Holtek's 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. Rev. 1.20 12 November 04, 2013