Data Sheet Rev. 1.00 / June 2012 ZSLS7025 Boost LED Driver ZSLS7025 Boost LED Driver Brief Description Features The ZSLS7025, one of our ZSLS Family of LED control ICs, is a constant current boost converter designed for driving high-brightness LEDs. It is optimal for driving multiple white LEDs connected in series so that the LED current is uniform for better brightness and color control. The wide input range and high output current enables diverse industrial, after-market automotive, and consumer lighting applications. The ZSLS7025 output current is adjustable via an external current sense resistor and can deliver stable constant output current from a few milliamps up to 2A or higher. The ZSLS7025 drives a constant current into the load. The control loop features a pulse frequency modulated (PFM) architecture that is inherently stable and does not need loop compensation. The ZSLS7025 supports pulse-width modulation (PWM) or linear voltage dimming, which allows flexible control of the LED luminance. The ZSLS7025 can operate in applications with a wide input voltage range from 5V to 100V. An integrated over-voltage protection (OVP) circuit protects the system, even under no-load conditions. The over-voltage protection is adjustable via external resistors R1 and R2. Wide application input voltage range: 5V to 100V (Higher voltage supported. See section 2.1 in the data sheet.) Constant current output limited only by external component selection No loop compensation required Internal over-voltage protection Internal over-temperature protection Brightness control via PWM or DC voltage control signal input SOP-8 package Benefits High efficiency: up to 95% Minimum bill of materials Small form-factor package Available Support Demonstration Kit Physical Characteristics Junction temperature: -40°C to 125°C RoHS compliant For additional information on our LED driver family, visit www.zmdi.com/products/led-drivers/ ZSLS7025 Typical Application Circuit VIN =5 to 100 VDC L1 CIN RVDD ZSLS7025 VDD CVDD GATE TOFF CS ADJ FB GND RTOFF D1 Q1 R1 COUT LED String OVP RCS R2 RFB © 2012 Zentrum Mikroelektronik Dresden AG — Rev. 1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. ZSLS7025 Boost LED Driver ZSLS7025 Block Diagram 5 to 100 VDC VIN L1 RVDD D1 5V Clamp VDD CIN Voltage Regulator Block 1 CVDD Current Mirror ZSLS7025 Vref1 (1.0V) Vref2 (0.3V) TOFF COUT 2 Vref3 (0.25V) RTOFF Vref4 (0.05V) + VDD - Vref4 50k ADJ 3 Vref1 + Q1 Blanking 500ns 900k S n LED R Q 100k GATE - 5 + FB CS + 6 Vref3 UVLO + Vref2 7 R1 - POR OVP + Vref1 8 RCS GND R2 RFB 4 Typical Applications Retro-fit Lighting Architectural/Building Lighting MR16 Lights Replacement Tubes SELV Lighting LED Backlighting Signage and Outdoor Lighting General Purpose Low-Voltage Industrial and Consumer Applications Ordering Information Product Sales Code Description Package ZSLS7025-ZI1R ZSLS7025 – Boost LED Driver SOP-8 (Tape & Reel) ZSLS7025KIT-D1 ZSLS7025PCB-D1 Demo Board, 1 ZLED-PCB10, and 5 ZSLS7025 ICs Kit Sales and Further Information Zentrum Mikroelektronik Dresden AG Grenzstrasse 28 01109 Dresden Germany ZMD America, Inc. 1525 McCarthy Blvd., #212 Milpitas, CA 95035-7453 USA Phone +49 (0)351.8822.7.533 Phone +855-ASK-ZMDI Fax +49 (0)351.8822.8.7533 (+855.275.9634) www.zmdi.com [email protected] Zentrum Mikroelektronik Dresden AG, Japan Office 2nd Floor, Shinbashi Tokyu Bldg. 4-21-3, Shinbashi, Minato-ku Tokyo, 105-0004 Japan ZMD FAR EAST, Ltd. 3F, No. 51, Sec. 2, Keelung Road 11052 Taipei Taiwan Zentrum Mikroelektronik Dresden AG, Korean Office POSCO Centre Building West Tower, 11th Floor 892 Daechi, 4-Dong, Kangnam-Gu Seoul, 135-777 Korea Phone +81.3.6895.7410 Fax +81.3.6895.7301 Phone +886.2.2377.8189 Fax +886.2.2377.8199 Phone +82.2.559.0660 Fax +82.2.559.0700 DISCLAIMER: This information applies to a product under development. Its characteristics and specifications are subject to change without notice. Zentrum Mikroelektronik Dresden AG (ZMD AG) assumes no obligation regarding future manufacture unless otherwise agreed to in writing. The information furnished hereby is believed to be true and accurate. However, under no circumstances shall ZMD AG be liable to any customer, licensee, or any other third party for any special, indirect, incidental, or consequential damages of any kind or nature whatsoever arising out of or in any way related to the furnishing, performance, or use of this technical data. ZMD AG hereby expressly disclaims any liability of ZMD AG to any customer, licensee or any other third party, and any such customer, licensee and any other third party hereby waives any liability of ZMD AG for any damages in connection with or arising out of the furnishing, performance or use of this technical data, whether based on contract, warranty, tort (including negligence), strict liability, or otherwise. © 2012 Zentrum Mikroelektronik Dresden AG — Rev. 1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. ZSLS7025 Boost LED Driver Contents 1 2 3 4 IC Characteristics .......................................................................................................................................................... 6 1.1 Absolute Maximum/Minimum Ratings .................................................................................................................... 6 1.2 Operating Conditions ............................................................................................................................................. 6 1.3 Electrical Parameters ............................................................................................................................................. 7 1.4 Typical Performance Characteristics Graphs ......................................................................................................... 8 Circuit Description ....................................................................................................................................................... 10 2.1 ZSLS7025 Overview ............................................................................................................................................ 10 2.2 Boost Converter ................................................................................................................................................... 10 2.3 Internal 5V Regulator ........................................................................................................................................... 11 2.4 Input Current ........................................................................................................................................................ 11 2.5 LED Current Control ............................................................................................................................................ 11 2.6 Dimming Control .................................................................................................................................................. 11 2.6.1 Dimming Control Using an External DC Control Signal ................................................................................ 12 2.6.2 Dimming Control Using an RC Filter to Convert a PWM Signal to a DC Voltage.......................................... 13 2.6.3 PWM Dimming with a Dimming Control MOSFET (Q2)................................................................................. 14 2.7 Peak Input Current Control .................................................................................................................................. 14 2.8 Setting the Minimum Off-Time tOFF_MIN ................................................................................................................. 15 2.9 Switching Frequency and Inductor Value ............................................................................................................. 15 2.10 DC Power Loss .................................................................................................................................................... 16 Operating Conditions ................................................................................................................................................... 17 3.1 Under-Voltage Lockout ........................................................................................................................................ 17 3.2 Over-Voltage Protection ....................................................................................................................................... 17 Application Circuit Design............................................................................................................................................ 18 4.1 Applications.......................................................................................................................................................... 18 4.2 External Component Selection............................................................................................................................. 18 4.2.1 Series Resistor RVDD ..................................................................................................................................... 18 4.2.2 Inductor L1 .................................................................................................................................................... 18 4.2.3 High Frequency Noise Filter Capacitor CVDD ................................................................................................ 19 4.2.4 Input Capacitor CIN ....................................................................................................................................... 19 4.2.5 Output Capacitor COUT for Reducing Output Ripple ...................................................................................... 19 4.2.6 Schottky Rectifier Diode D1........................................................................................................................... 19 4.2.7 External MOSFET Q1.................................................................................................................................... 19 4.3 Application Circuit Layout Requirements ............................................................................................................. 20 4.4 Application Example ............................................................................................................................................ 20 4.4.1 Selecting RVDD, CIN, and CVDD ....................................................................................................................... 21 4.4.2 Selecting RTOFF to Set Minimum tOFF............................................................................................................. 21 4.4.3 Selecting RFB to Set Output Current and C3 ................................................................................................. 21 4.4.4 Selecting R3, R4, R5 and C1 .......................................................................................................................... 22 4.4.5 RCS for Setting Input Peak Current ............................................................................................................... 23 Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 4 of 27 ZSLS7025 Boost LED Driver 4.4.6 L1 for Setting the Frequency ......................................................................................................................... 23 4.4.7 R1 and R2 for Setting OVP ............................................................................................................................ 24 4.4.8 Q1 External MOSFET and D1 Diode ............................................................................................................. 24 5 ESD Protection ............................................................................................................................................................ 25 6 Pin Configuration and Package ................................................................................................................................... 25 7 Glossary ...................................................................................................................................................................... 27 8 Ordering Information ................................................................................................................................................... 27 9 Document Revision History ......................................................................................................................................... 27 List of Figures Figure 1.1 VIN vs. IOUT with VOUT = 40V ............................................................................................................................ 8 Figure 1.2 VIN vs. Efficiency with VOUT = 40V ................................................................................................................... 8 Figure 1.3 VOUT vs. IOUT with VIN = 12V ............................................................................................................................ 8 Figure 1.4 VOUT vs. Efficiency with VIN = 12V................................................................................................................... 8 Figure 1.5 VIN vs. IOUT with VOUT = 48V ............................................................................................................................ 8 Figure 1.6 VIN vs. Efficiency with VOUT = 48V................................................................................................................... 8 Figure 1.7 VOUT vs. IOUT with VIN = 24V ............................................................................................................................ 9 Figure 1.8 VOUT vs. Efficiency with VIN = 24V................................................................................................................... 9 Figure 2.1 Typical ZSLS7025 Circuit Diagram ............................................................................................................... 10 Figure 2.2 Example Circuit for Controlling Output Current via an External DC Control Voltage .................................... 12 Figure 2.3 RC Filter PWM Dimming Circuit ................................................................................................................... 13 Figure 2.4 PWM Dimming Circuit Using a Dimming Control MOSFET (Q 2) .................................................................. 14 Figure 2.5 Minimum Off-Time tOFF_MIN vs. RTOFF ............................................................................................................ 15 Figure 4.1 Typical ZSLS7025 Application Circuit ........................................................................................................... 18 Figure 4.2 Application Design Example – RC Filter PWM Dimming Circuit ................................................................... 21 Figure 6.1 ZSLS7025 Pin Assignments ......................................................................................................................... 25 Figure 6.2 SOP-8 Package Dimensions and Pin Assignments ...................................................................................... 26 List of Tables Table 1.1 Absolute Maximum Ratings ............................................................................................................................ 6 Table 1.2 Operating Conditions ...................................................................................................................................... 6 Table 1.3 Electrical Parameters ..................................................................................................................................... 7 Table 6.1 Pin Description SOP-8 .................................................................................................................................. 25 Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 5 of 27 ZSLS7025 Boost LED Driver 1 IC Characteristics Stresses beyond those listed under “Absolute Maximum/Minimum Ratings” (section 1.1) 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 recommended under “Recommended Operating Conditions” (section 1.2) is not implied. Exposure to absolute–maximum conditions for extended periods may affect device reliability. 1.1 Absolute Maximum/Minimum Ratings Table 1.1 Absolute Maximum Ratings No. PARAMETER SYMBOL 1.1.1 Voltage on VDD pin (also see specification 1.2.2 and 1.2.3) VDD 1.1.2 All other pins to GND 1.1.3 Maximum input current on 1) VDD pin 1.1.4 ESD performance 1.1.5 Junction temperature TjMAX 1.1.6 Storage temperature TST 1) 1.2 CONDITIONS MIN TYP MAX UNIT -0.3 6 V -0.3 6 V 10 mA ±3.5 kV -40 150 °C -65 150 °C MAX UNIT -40 125 °C IDD Human Body Model Exceeding VDD maximum input current could cause the pin to not clamp at 5V. Operating Conditions Table 1.2 Operating Conditions No. PARAMETER 1.2.1 Junction temperature 1) 1.2.2 Supply voltage (also see specification 1.1.1) 1.2.3 VDD pin (also see specification 1.1.1) 1) 2) SYMBOL CONDITIONS TOP Supply voltage connected to VDD pin via series resistor RVDD (see section 4.2.1) 5 100 V VDD Supply voltage connected to VDD pin via series resistor RVDD (see section 4.2.1) 4.3 5.6 V Supply voltage should be connected to the VDD pin via RVDD. 2) Voltage set according to the clamping of the internal shunt regulator (see section 2.3). June 28, 2012 TYP VIN 1) Data Sheet MIN © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 6 of 27 ZSLS7025 Boost LED Driver 1.3 Electrical Parameters Except as noted, test conditions for the following specifications are VIN = 10V, RVDD = 10KΩ, ADJ floating, and TOP = 25°C (typical). Production testing of the chip is performed at 25°C unless otherwise stated. Functional operation of the chip and specified parameters at other temperatures are guaranteed by design, characterization, and process control. Table 1.3 Electrical Parameters No. PARAMETER SYMBOL 1.3.1 VDD pin clamp voltage VDD 1.3.2 Under-voltage threshold VUVLO_TH 1.3.3 Under-voltage threshold hysteresis VUVLO_HYS 1.3.4 Quiescent supply current ISS CONDITIONS MIN TYP MAX UNIT RVDD = 10KΩ 4.3 5 5.6 V VDD rising 2.0 2.7 3.0 V 300 mV VDD = 5V 250 400 μA VDD = 2.5V (under-voltage) 50 75 μA 240 265 mV 1.3.5 Peak-current sense threshold voltage VCS_TH ADJ pin = 5V 1.3.6 Peak current sense blanking interval tBLANK VCS=VCS_TH + 50mV 500 ns 1.3.7 Fixed turn-off interval RTOFF = 250KΩ 10 μs 0.5 V 2.4 V TOTP 125 °C TOTP_HYS 20 °C tOFF 215 Peak-current control low threshold voltage 1.3.8 Peak-current control high threshold voltage VADJ 1.3.9 Over-temperature protection (OTP) threshold 1.3.10 OTP threshold hysteresis 1.3.11 Internal feedback reference voltage VFB 0.29 0.3 0.31 V 1.3.12 Over-voltage input threshold VOVP_TH 0.9 1.0 1.1 V Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 7 of 27 ZSLS7025 Boost LED Driver 1.4 Typical Performance Characteristics Graphs Figure 1.1 VIN vs. IOUT with VOUT = 40V Figure 1.2 VIN vs. Efficiency with VOUT = 40V Figure 1.3 VOUT vs. IOUT with VIN = 12V Figure 1.4 VOUT vs. Efficiency with VIN = 12V Figure 1.5 VIN vs. IOUT with VOUT = 48V Figure 1.6 VIN vs. Efficiency with VOUT = 48V Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 8 of 27 ZSLS7025 Boost LED Driver Figure 1.7 VOUT vs. IOUT with VIN = 24V Figure 1.8 VOUT vs. Efficiency with VIN = 24V _ Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 9 of 27 ZSLS7025 Boost LED Driver 2 Circuit Description 2.1 ZSLS7025 Overview The ZSLS7025 is a constant current boost converter. Its output current is adjustable via an external current sense resistor, and it can deliver stable constant output current from a few milliamps up to 2A or higher. The ZSLS7025 drives a constant current into the load, automatically adjusting the output voltage according to the load. The control loop features a pulse frequency modulated (PFM) architecture that is inherently stable and does not need loop compensation. The ZSLS7025 can operate in applications with a wide input voltage range from 5V to 100V. VIN voltages above 100V can be supported if logic level MOSFETs for the higher voltage rating are available. An integrated overvoltage protection (OVP) circuit protects the system, even under no-load conditions. The over-voltage protection is adjustable via external resistors R1 and R2. The minimum load voltage must always be higher than the maximum VIN, and the drain voltage rating of the switching transistor (Q 1) must be higher than the over-voltage shut-off limit. Note: The ZSLS7025 has an internal 5V shunt regulator connected to the VDD pin. The RVDD series resistor must be connected between the VDD pin and VIN to limit current flow. See section 4.2 for requirements for selecting the external components referred to in the following sections. Figure 2.1 Typical ZSLS7025 Circuit Diagram VIN =5 to 100 VDC L1 CIN RVDD ZSLS7025 VDD CVDD 2.2 GATE TOFF CS ADJ FB GND RTOFF D1 Q1 R1 COUT LED String OVP RCS R2 RFB Boost Converter The ZSLS7025's boost converter uses a peak-current mode topology. The CS pin voltage in conjunction with the current-sense resistor RCS determines the peak current in the inductor (L1). Q1 is turned on and off by the output of an RS flip-flop that is set when the voltage on the FB pin drops below the internal threshold of 300 mV. After Q1 has been switched on, a blanking timer disables the current sense input CS to avoid immediate spurious shut-off as a result of the switching transient when Q1 discharges the parasitic capacitances on its drain node to ground. After the blanking time tBLANK (see parameter 1.3.6 in section 1.3) has elapsed, the current through the inductor is sensed as a voltage drop across RCS, and when the voltage reaches the peak-current sense threshold voltage VCS_TH (see parameter 1.3.5 in section 1.3), the flip-flop is reset and Q1 is turned off. Once Q1 is turned off, the inductor reverses polarity, providing the voltage boost, and the inductor current will decrease until the input voltage on the FB pin drops below the internal feedback reference voltage VFB, (see parameter 1.3.11 in section 1.3). Q1 is then turned on again, and this operation repeats in each cycle. Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 10 of 27 ZSLS7025 Boost LED Driver When the input voltage on the FB pin does not exceed the internal feedback reference voltage VFB, such as during start-up, Q1 will remain off for the configured minimum tOFF time (see sections 2.8 and 2.9), and then it is switched on again. 2.3 Internal 5V Regulator The ZSLS7025 includes an internal 5V (typical) shunt regulator connected to the VDD pin which maintains a 5V power supply for the gate driver and control circuitry. Connect VIN to the VDD pin via the current limiting series resistor RVDD (see section 4.2.1 for required values). Consideration should be given to the tolerances on the VDD pin operating conditions (see section 1.2, parameter 1.2.3) and VIN. 2.4 Input Current The current required by the ZSLS7025 is 0.25mA (typical) plus the switching current of the external MOSFET, Q1. The switching frequency of Q1 affects the amount of current required, as does Q1's gate charge requirement (found in the MOSFET manufacturer's data sheet). IIN 0.25mA QG fS (1) Where fS = switching frequency of Q1 QG = gate charge of Q1 2.5 LED Current Control The ZSLS7025 regulates the LED current by sensing the voltage across the external feedback resistor RFB in series with the LEDs. The voltage is sensed via the FB pin where the internal feedback reference voltage VFB is 0.3V (typical; see section 1.3, parameter 1.3.11). The LED current can easily be set according to equation (2). IOUT VFB 0.3V RFB RFB (2) Where IOUT = Average output current through the LED(s) in amperes VFB = Internal feedback reference voltage Note: For an accurate LED current, a precision resistor is required for RFB (1% is recommended). 2.6 Dimming Control There are three options for LED dimming: DC voltage dimming control RC-filtered PWM signal dimming control PWM signal with a dimming control MOSFET(Q2) Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 11 of 27 ZSLS7025 Boost LED Driver 2.6.1 Dimming Control Using an External DC Control Signal The LED output current can be set below the nominal average value defined by equation (2) using an external DC voltage control signal superimposed on the FB pin as shown in the example circuit in Figure 2.2. As the DC control signal, VDC, increases, the current through R3 increases with a subsequent increase in the voltage at the FB pin. This causes the ZSLS7025 to compensate by reducing the output current through the LED string. Consequently, the output current is inversely proportional to the DC control voltage. Note: It is important to ensure that the LED output voltage VOUT remains higher than the input voltage VIN in dimming applications. The output current controlled by the DC voltage on FB can be calculated using equation (3). IOUT R VDC VFB VFB 3 R4 RFB (3) Where IOUT = Output current through the LED(s) with a DC control voltage VFB = Internal feedback reference voltage (see section 1.3, parameter 1.3.11) VDC = External DC control voltage Figure 2.2 Example Circuit for Controlling Output Current via an External DC Control Voltage VIN =5 to 100 VDC L1 CIN RVDD ZSLS7025 VDD CVDD GATE TOFF CS ADJ FB GND RTOFF D1 Q1 R1 COUT LED String R3 OVP R4 RCS R2 RFB DC Control Signal VDC = 0 to 5V Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 12 of 27 ZSLS7025 Boost LED Driver 2.6.2 Dimming Control Using an RC Filter to Convert a PWM Signal to a DC Voltage As shown in Figure 2.3, a filtered PWM signal can be used as an adjustable DC voltage for LED dimming control, and it functions the same as the DC control signal described in section 2.6.1. An external RC filter converts the PWM signal to a DC voltage, which is summed with the FB voltage to regulate the output current. Using a fixed frequency PWM signal and changing the duty cycle adjusts the average LED current. The LED current can be calculated with equation (4): IOUT R VPWM DPWM VFB VFB 3 R 4 R5 RFB (4) Where IOUT = Output current through the LED(s) with a PWM control voltage VFB = Internal feedback reference voltage (see section 1.3, parameter 1.3.11) VPWM = External PWM control voltage DPWM = Duty cycle of the PWM control signal The LED current is inversely proportional to the PWM duty cycle; i.e., when the PWM signal has a 100% duty cycle, the output current is minimum, ideally zero, and when the PWM signal has a 0% duty cycle, the output current is at its maximum. See the example in section 4.4 for more details. Note: Care must be taken to ensure that the minimum required current is not already exceeded when the LEDs are connected to VIN. Figure 2.3 RC Filter PWM Dimming Circuit VIN =5 to 100 VDC L1 CIN RVDD ZSLS7025 VDD TOFF ADJ CVDD GND RTOFF D1 GATE Q1 R1 COUT LED String CS FB R3 OVP RCS R2 R5 R4 RFB C1 PWM Control Signal - Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 13 of 27 ZSLS7025 Boost LED Driver 2.6.3 PWM Dimming with a Dimming Control MOSFET (Q2) Figure 2.4 shows the configuration for using an external PWM signal with a dimming control MOSFET Q2. When the PWM input is high (VH>2.4V), Q2 is on and the ZSLS7025 operates normally to regulate the output current. When the PWM signal is low (VL<0.5V), Q2 is off; the input voltage on the FB pin will be below VFB and the ZSLS7025 is shutdown. Using a fixed frequency PWM signal and changing the duty cycle adjusts the average LED current. The recommended 5V PWM frequency is between 200Hz and 1KHz. Figure 2.4 PWM Dimming Circuit Using a Dimming Control MOSFET (Q2) VIN =5 to 100 VDC L1 CIN RVDD GATE TOFF CS ADJ FB GND RTOFF LED String ZSLS7025 VDD CVDD D1 Q1 R1 COUT Q2 OVP RCS R2 RFB PWM Control Signal 2.7 Peak Input Current Control The ZSLS7025 limits the peak inductor current and therefore the peak input current through the feedback path of RCS connected from the source of the external MOSFET (Q1) to ground. The required average input current is based on the boost ratio VOUT/VIN and the designed value for average LED current. The required average input current can be calculated with equation (5): IIN _ AVG VOUT IOUT VIN (5) Where = Assumed power conversion efficiency (recommended value for calculation: 0.9) Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 14 of 27 ZSLS7025 Boost LED Driver In general, setting the peak inductor current to 1.5 times the average input current is sufficient to maintain good regulation of the output current. IIN _ PEAK 1.5 IIN _ AVG VCS _ TH (6) RCS Where VCS_TH = VADJ/10 if 0.5V < VADJ ≤ 2.4V or VCS_TH = 0.24V if VADJ > 2.4V or if the ADJ pin is floating 2.8 Setting the Minimum Off-Time tOFF_MIN The ZSLS7025 operates in a pulsed frequency modulation (PFM) mode. In nominal operation, on-time and offtime are determined according to equations (8), (9), (10), and (11). In most applications, the recommended value for tOFF_MIN is 1µs. The relationship between tOFF_MIN and RTOFF is shown in equation (7) and Where tOFF_MIN is in µs and RTOFF is in Ω. Figure 2.5. tOFF_MIN is valid as long as VFB has not reached the threshold of 300 mV. t OFF _ MIN 40 1012 RTOFF (7) Where tOFF_MIN is in µs and RTOFF is in Ω. Minimum Off-Time tOFF_MIN vs. RTOFF tOFF_MIN_IN µs Figure 2.5 Minimum tOFF_MIN is 1µs RTOFF Value in kΩ 2.9 Switching Frequency and Inductor Value The inductance value of the inductor (L1) directly determines the switching frequency of the converter. Under fixed conditions, the inductance is inversely proportional to the switching frequency; i.e., the larger the inductance, the lower the switching frequency. A higher switching frequency will reduce the value required for the inductor but will increase the switching loss in the external MOSFET, Q1 (see section 2.4). Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 15 of 27 ZSLS7025 Boost LED Driver The switching frequency f in Hertz can be calculated from tON and tOFF in seconds with equation (8). f tON 1 t OFF (8) The ripple current in the inductor can be calculated with equation (9). IRIPPLE 2 IIN _ PEAK IIN _ AVG (9) The Q1 on-time, tON, can be calculated with equation (10). t ON (IRIPPLE L1) VIN IIN_AVG RL RDS(ON) RCS (10) Where RL = the DC resistance of inductor L1 in Ω RDS(ON) = the on-resistance of Q1 in Ω (see manufacturer's specifications) L1 = the value of the inductor L1 in Henries The Q1 off-time, tOFF, can be calculated with equation (11). t OFF IRIPPLE L1 VOUT VD IIN_AVG RL VIN (11) Where VD = the forward voltage of the diode D1 at the required load current in volts Note: The selection of inductor L1 must ensure that tOFF is longer than the tOFF_MIN as calculated in equation (7). If not, the converter cannot output the required current. The recommended switching frequency is 20kHz < f < 200kHz. Lower than 20KHz will cause audio noise of the inductor, and a frequency that is too high will increase the switching loss in Q1. With a fixed VIN, VOUT, IIN_AVG, and IIN_PEAK, the switching frequency is inversely proportional to the inductor value. 2.10 DC Power Loss The RDS (ON) of the external MOSFET, Q1, determines the DC power loss, which can be calculated with equation (12). V 2 2 PDISS IIN_AVG RDS(ON) DQ1 IIN_AVG RDS(ON) 1 IN VOUT 1 η (12) Where DQ1 = the duty cycle for Q1 = Assumed power conversion efficiency (recommended value for calculation: 0.9) Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 16 of 27 ZSLS7025 Boost LED Driver 3 Operating Conditions 3.1 Under-Voltage Lockout The under-voltage lockout (UVLO) function monitors the voltage on the ZSLS7025’s VDD pin. If this voltage is lower than the UVLO threshold minus the UVLO hysteresis (VUVLO_TH - VUVLO_HYS), the ZSLS7025 is disabled. If the voltage on the VDD pin reaches a level higher than the UVLO threshold (VUVLO_TH), the lock-out function turns off and the ZSLS7025 is re-enabled. See parameters 1.3.2 and 1.3.3 in section 1.3 for the VUVLO_TH threshold and VUVLO_HYS hysteresis, respectively. 3.2 Over-Voltage Protection Open-load protection is achieved through the ZSLS7025's over-voltage protection (OVP). In boost converters, an LED string failure can cause the feedback voltage (VFB) to always be zero. If this happens, the ZSLS7025 will keep boosting the output voltage higher and higher. If the output voltage reaches the programmed OVP threshold, the protection mechanism will be triggered and stop the switching action. To ensure that the circuit functions properly, the OVP setting resistor divider, R1 and R2, must be set with appropriate values given by equation (13). The recommended OVP voltage is either 1.25 times the normal output voltage or 5V higher than the normal output voltage, whichever is higher. VOVP VOVP _ TH (R1 R2 ) R2 (13) Where VOVP_TH = Over-voltage input threshold: 1.0V (typical; see parameter 1.3.12 in section 1.3) VOVP = Output voltage OVP level Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 17 of 27 ZSLS7025 Boost LED Driver 4 Application Circuit Design 4.1 Applications The ZSLS7025 is ideal for driving white HB-LEDs in diverse industrial, after-market automotive, and consumer lighting applications using low supply voltages, such as SELV applications. It is optimal for driving multiple white HB-LEDs connected in series so that the LED current is uniform for better brightness and color control. It features a wide input range and high output current. Figure 4.1 demonstrates the typical application with the external components described in section 4.2. Figure 2.2, Figure 2.3, and Figure 2.4 demonstrate various dimming applications. Figure 4.1 Typical ZSLS7025 Application Circuit VIN =5 to 100 VDC L1 CIN RVDD ZSLS7025 VDD CVDD GATE TOFF CS ADJ FB GND RTOFF 4.2 D1 Q1 R1 COUT LED String OVP RCS R2 RFB External Component Selection Note: Also see section 4.3 for layout guidelines for the following external components. 4.2.1 Series Resistor RVDD The ZSLS7025 has an internal 5V shunt regulator connected to the VDD pin. The RVDD series resistor must be connected between the VDD pin and VIN to limit current flow. See section 2.1 regarding input voltages over 100V. 4.2.2 Inductor L1 See section 2.9 for calculating the proper value for L 1. Select an inductor with a current rating higher than the input average current and a saturation current over the calculated peak current. To calculate the worst case inductor peak current, use the minimum input voltage, maximum output voltage, and maximum total LED current. 2 Also ensure that the inductor has a low DCR (copper wire resistance) to minimize the I R power loss. Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 18 of 27 ZSLS7025 Boost LED Driver 4.2.3 High Frequency Noise Filter Capacitor CVDD External capacitor CVDD forms a high-frequency noise filter for the VDD pin. For all configurations, use CVDD to bypass the VDD pin using a low ESR capacitor (a 10µF ceramic capacitor is recommended) to provide a high frequency path to GND. 4.2.4 Input Capacitor CIN The CIN input capacitor connected to VIN will supply the transient input current for the power inductor. A value of 100μF or higher is recommended to prevent excessive input voltage ripple. Also see section 4.2.3. 4.2.5 Output Capacitor COUT for Reducing Output Ripple The output capacitor (COUT) holds the output current while the Q1 external MOSFET turns ON. This capacitor directly impacts the line regulation and the load regulation. Using a low ESR capacitor can minimize output ripple voltage and improve output current regulation. For most applications, a 220μF low ESR capacitor will be sufficient. Proportionally lower ripple can be achieved with higher capacitor values. 4.2.6 Schottky Rectifier Diode D1 The D1 external diode for the ZSLS7025 should be a Schottky diode with a low forward voltage drop and fast switching speed. The diode’s average current rating must exceed the application’s average output current. The diode’s maximum reverse voltage rating must exceed the over-voltage protection of the application. For PWM dimming applications, note the reverse leakage of the Schottky diode. Lower leakage current will drain the output capacitor less during PWM low periods, allowing for higher PWM dimming ratios. 4.2.7 External MOSFET Q1 The Q1 external MOSFET must have a VDS rating that exceeds the maximum over-voltage protection (OVP) level configured for the application. The VGS(th) of the MOSFET should be not higher than 4V. The MOSFET’s current rating must be higher than the input peak current (IIN_PEAK). Determine the power dissipation within Q1 and check if the thermal resistance of the MOSFET package causes the junction temperature to exceed maximum ratings. Also see section 2.10 regarding the effect of the MOSFET RDS(ON) on DC power loss. Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 19 of 27 ZSLS7025 Boost LED Driver 4.3 Application Circuit Layout Requirements The guidelines in this section are strongly recommended when laying out application circuits. As for all switching power supplies, especially those providing high current and using high switching frequencies, layout is an important design step. If the layout is not well-designed, the regulator could show instability as well as EMI problems. For additional guidelines, refer to the ZMDI application note PCB Layout Design Guidelines for LED Driver Circuits available at www.zmdi.com/products/led-drivers/. Wide traces should be used for connection of the high current loop to minimize the EMI and unnecessary loss. The external components ground should be connected to the ZSLS7025 ground and should be as short as possible. It is especially important that the RFB ground to ZSLS7025 ground connection is as short and wide as possible to have an accurate LED current. The capacitors CIN, CVDD, and COUT should be placed as close as possible to the ZSLS7025 for good filtering. It is especially important that the COUT output capacitor connection is as short and wide as possible. The Q1 external MOSFET drain is a fast switching node (also applies to Q2 if the PWM is accomplished with a dimming control MOSFET as described in section 2.6.3). The inductor L1 and Schottky diode D1 should be placed as close as possible to the drain, and the connection should be kept as short and wide as possible. Avoid other traces crossing and routing too long in parallel with this node to minimize the noise coupling into these traces. The feedback pins (i.e., CS, FB, OVP) should be as short as possible and routed away from the inductor, Schottky diode, and Q1. The feedback pins and feedback network should be shielded with a ground plane or trace to minimize noise coupling into this circuit. The thermal pad on the back of the external MOSFET package must be soldered to the large ground plane for ideal heat distribution. 4.4 Application Example This section provides an example of an application design for the ZSLS7025 for the RC-filter PWM application described in section 2.6.2 and shown again for reference in Figure 4.2. Design criteria: VIN = 12 to 24 V IOUT = 350mA VOUT = 30 to 40V (9 to 12 LEDs, Vf = 3.3V) To calculate the worst case parameters, use the minimum input voltage, maximum output voltage, and maximum output current; i.e., VIN = 12V, IOUT = 350mA, and VOUT ≈ 40V (12 LEDs, Vf = 3.3V). Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 20 of 27 ZSLS7025 Boost LED Driver Application Design Example – RC Filter PWM Dimming Circuit Figure 4.2 VIN L1 CIN RVDD ZSLS7025 VDD CVDD D1 GATE TOFF CS ADJ FB GND Q1 R1 COUT LED String R3 OVP RCS RTOFF R2 R5 R4 RFB C1 PWM Control Signal 4.4.1 Selecting RVDD, CIN, and CVDD Assume IIN = 2.5mA. R VDD VIN VDD 3k IIN (14) Choose CIN as 220μF/35V and CVDD as 10μF/16V. 4.4.2 Selecting RTOFF to Set Minimum tOFF The recommended value for tOFF_MIN is 1μs. t OFF _ MIN 40 1012 RTOFF 1s (15) Choose RTOFF = 24kΩ. 4.4.3 Selecting RFB to Set Output Current and C3 RFB VFB _ TH IOUT 0.86 (16) Choose C3 = 220μF/63V (low ESR electrolytic capacitor). Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 21 of 27 ZSLS7025 Boost LED Driver 4.4.4 Selecting R3, R4, R5 and C1 R3, R4, and R5 can be obtained by IOUT R VPWM DPWM VFB VFB 3 R 4 R5 RFB (17) Substitute DPWM=100%, VPWM = 5V, and IOUT =0 in the equation, and the result is R 5 100% 0.3 0.3 3 R 4 R5 0 0.86 (18) which can be simplified to 15.66 x R3 = R4 + R5 The low pass filter formed by R5 and C1 must have a corner frequency much lower than the PWM frequency. As the corner frequency of the filter decreases, the response time of the LED current to changes in PWM increases. Choose a corner frequency 50 times lower than fPWM. R5 C1 50 2fPWM (19) Assume fPWM is 200Hz (or higher) and choose C1 = 0.1μF, and the result is R5 ≥400kΩ. Choose C4 = 0.1μF, R5 = 400kΩ. Choose a nominal value for R4, and then calculate R3. Choose R4 = 10kΩ, then R3 = 26.2kΩ. Substitute DPWM=0, VPWM = 5V and IOUT = 350mA in the equation, and the result is IOUT R VPWM DPWM VFB 0.3 26.2 5 0% 0.3 VFB 3 R R 400 10 4 5 0.35A RFB RFB (20) So, RFB =0.91Ω. (With the RC filter PWM dimming, RFB will be different than in the no dimming application shown in Figure 2.1.) Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 22 of 27 ZSLS7025 Boost LED Driver 4.4.5 RCS for Setting Input Peak Current Assume that VOUT IOUT VIN IIN _ PEAK 1.5 IIN _ AVG 1.5 1.5 (21) 40 0.35 1.95A 12 0.9 Where η is the assumed power conversion efficiency (the recommended value for this calculation is 0.9) RCS VCS _ TH IIN _ PEAK 0.123 (22) Choose RCS = 0.123Ω, IIN_PEAK=1.95A 4.4.6 L1 for Setting the Frequency Input average current: IIN _ AVG VOUT IOUT 1.3A VIN (23) The ripple current in the inductor: IRIPPLE 2 IIN _ PEAK IIN _ AVG 1.3A (24) According to tOFF > tOFF_MIN: t OFF VOUT IRIPPLE L1 1µs VD (IIN_AVG RL ) VIN (25) This gives L1 > 22μH. Assume L1 = 22μH and RL + RDS(ON) +RCS=0.4Ω t ON (IRIPPLE L1) 2.5s VIN IIN _ AVG RL RDS(ON ) RCS (26) Then the assumed switching frequency: f' Data Sheet June 28, 2012 t ON 1 285kHz t OFF © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. (27) 23 of 27 ZSLS7025 Boost LED Driver The recommended switching frequency, 20KHz < f < 200KHz, according to the switching frequency, is inversely proportional to the inductor value; for example, select L1=100 μH. Therefore f f ' 22 63kHz 100 (28) The saturation current of the inductor must exceed the input peak current (IIN_PEAK). 4.4.7 R1 and R2 for Setting OVP Set VOVP = VOUT + 5V = 45V VOVP VOVP _ TH (R1 R2 ) R2 (29) Choose R2 =10kΩ, then R1 = 470kΩ. 4.4.8 Q1 External MOSFET and D1 Diode Power losses in the Q1 external MOSFET should be minimized. Conduction losses increase with RDS(on), and switching losses increase with gate/drain charge and frequency. Therefore, selecting a MOSFET with low RDS(on) and low gate/drain charge for the Q1 external MOSFET will help to optimize efficiency. The MOSFET’s current rating must be higher than the input peak current IIN_PEAK. Q1 must have a VDS rating that exceeds the maximum over-voltage protection (OVP) level configured for the application. The average and peak current of the diode D1 must exceed the output average current and input peak current. The diode’s maximum reverse voltage rating must exceed the over-voltage protection of the application. Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 24 of 27 ZSLS7025 Boost LED Driver 5 ESD Protection All pins have an ESD protection of ±3500V according to the Human Body Model (HBM). The ESD test follows the Human Body Model based on MIL 883-H, Method 3015.8. 6 Pin Configuration and Package Figure 6.1 ZSLS7025 Pin Assignments Table 6.1 Pin Description SOP-8 Pin Name NO. VDD 1 Positive power supply input pin. Internally clamped at 5V (typical). TOFF 2 Pin for setting off time. An external resistor, RTOFF, connected to this pin forms an RC discharge path to generate the constant minimum off time of the Q1 external MOSFET. ADJ 3 Enable and input peak current control pin. This pin is pulled up to 4.5V internally to set VCS_TH =0.24V if ADJ is floating. If VADJ<0.5V, the Q1 external MOSFET shuts down. If 0.5 VADJ 2.4V, VCS_TH = VADJ/10. If VADJ>2.4V, VCS_TH =0.24V. GND 4 Ground. GATE 5 Driver’s output for the gate of the Q1 external MOSFET. CS 6 Current sense input for the boost, peak-current control loop. FB 7 Feedback voltage input pin. Used to regulate the current of the LEDs by keeping VFB=0.3V. OVP 8 Overvoltage protection input pin. If the voltage at OVP exceeds the over-voltage input threshold, VOVP_TH, the GATE output shuts down. Data Sheet June 28, 2012 Description © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 25 of 27 ZSLS7025 Boost LED Driver Figure 6.2 SOP-8 Package Dimensions and Pin Assignments SOP-8 Package Dimensions (mm, except θ) A 1.550 ± 0.200 E 3.900 ± 0.100 A1 0.175 ± 0.075 E1 6.000 ± 0.200 A2 1.450 Typical e 1.270 Typical b 0.420 ± 0.090 L 0.835 ± 0.435 c 0.214 ± 0.036 θ 4° ± 4° D 4.900 ± 0.200 Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 26 of 27 ZSLS7025 Boost LED Driver 7 Glossary Term Description HB High Brightness OTP Over-Temperature Protection OVP Over-Voltage Protection RS Flip-Flop Reset-Set Flip-Flop UVLO Under-Voltage Lockout 8 Ordering Information Product Sales Code Description Package ZSLS7025-ZI1R ZSLS7025 – Boost LED Driver SOP-8 (Tape & Reel) ZSLS7025KIT-D1 ZSLS7025PCB-D1 Demo Board, 1 ZLED-PCB10, and 5 ZSLS7025 ICs Kit 9 Document Revision History Revision Date 1.00 June 28, 2012 Description First issue. Sales and Further Information Zentrum Mikroelektronik Dresden AG Grenzstrasse 28 01109 Dresden Germany ZMD America, Inc. 1525 McCarthy Blvd., #212 Milpitas, CA 95035-7453 USA Phone +49 (0)351.8822.7.533 Phone +855-ASK-ZMDI Fax +49 (0)351.8822.8.7533 (+855.275.9634) www.zmdi.com [email protected] Zentrum Mikroelektronik Dresden AG, Japan Office 2nd Floor, Shinbashi Tokyu Bldg. 4-21-3, Shinbashi, Minato-ku Tokyo, 105-0004 Japan ZMD FAR EAST, Ltd. 3F, No. 51, Sec. 2, Keelung Road 11052 Taipei Taiwan Zentrum Mikroelektronik Dresden AG, Korean Office POSCO Centre Building West Tower, 11th Floor 892 Daechi, 4-Dong, Kangnam-Gu Seoul, 135-777 Korea Phone +81.3.6895.7410 Fax +81.3.6895.7301 Phone +886.2.2377.8189 Fax +886.2.2377.8199 Phone +82.2.559.0660 Fax +82.2.559.0700 DISCLAIMER: This information applies to a product under development. Its characteristics and specifications are subject to change without notice. Zentrum Mikroelektronik Dresden AG (ZMD AG) assumes no obligation regarding future manufacture unless otherwise agreed to in writing. The information furnished hereby is believed to be true and accurate. However, under no circumstances shall ZMD AG be liable to any customer, licensee, or any other third party for any special, indirect, incidental, or consequential damages of any kind or nature whatsoever arising out of or in any way related to the furnishing, performance, or use of this technical data. ZMD AG hereby expressly disclaims any liability of ZMD AG to any customer, licensee or any other third party, and any such customer, licensee and any other third party hereby waives any liability of ZMD AG for any damages in connection with or arising out of the furnishing, performance or use of this technical data, whether based on contract, warranty, tort (including negligence), strict liability, or otherwise. Data Sheet June 28, 2012 © 2012 Zentrum Mikroelektronik Dresden AG — Rev.1.00 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 27 of 27