RT8494GS Evaluation Board your power partner. High Voltage High Current LED Driver Controller for Buck, Boost or Buck-Boost Topology Purpose The startup voltage of the RT8494 is around 4.5V. When VCC voltage is greater than 4.5V, the RT8494 starts operation and a regulated GBIAS supply voltage is generated by an internal LDO circuit. With VCC greater than 10V, the GBIAS supply will be regulated around 8.5V to supply the power for the internal GATE pin driver circuit. Table of Contents PURPOSE ................................................................................................................................................................................ 1 INTRODUCTION ...................................................................................................................................................................... 2 KEY PERFORMANCE SUMMARY TABLE .................................................................................................................................... 2 BENCH TEST SETUP CONDITIONS ............................................................................................................................................ 3 SCHEMATIC, BILL OF MATERIALS & BOARD LAYOUT ................................................................................................................. 5 MORE INFORMATION ............................................................................................................................................................. 8 IMPORTANT NOTICE FOR RICHTEK EVALUATION BOARD .......................................................................................................... 8 EVB_RT8494GS-00 December 2015 1 http://www.richtek.com RT8494GS Evaluation Board your power partner. Introduction General Product Information The RT8494 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. With a current sense amplifier threshold of 190mV, the LED current is programmable with one external current sense resistor. With the maximum operating input voltage of 36V and output voltage up to 90V, the RT8494 is ideal for Buck, Boost or Buck-Boost operation. With the switching frequency programmable over 100kHz to 1MHz, the external inductor and capacitors can be small while maintaining high efficiency. Dimming can be done by either analog or digital. The builtin clamping comparator and filter allow easy low noise analog dimming conversion from digital signal with only one external capacitor. The RT8494 is available in SOP-14 package. Product Feature High Voltage Capability : VIN up to 36V, LED Sensing Threshold Common Mode Voltage up to 90V Buck, Boost or Buck-Boost Operation Programmable Switching Frequency Easy Dimming Control : Analog or Digital Converting to Analog with One External Capacitor Programmable Soft-Start to Avoid Inrush Current Programmable Over-Voltage Protection VIN Under-Voltage Lockout and Thermal Shutdown AEC-Q100 Compliance Key Performance Summary Table Key Features Evaluation Board Number : PCB042_V1 Input Voltage Range 4.5V to 36V Input Threshold (VISP - VISN) 190mV Threshold Common Mode Voltage 90V Default Marking & Package Type RT8494GS, SOP-14 Switching Frequency Programmable Switching Frequency EVB_RT8494GS-00 December 2015 2 http://www.richtek.com RT8494GS Evaluation Board your power partner. Bench Test Setup Conditions Headers Description and Placement Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to [email protected] Test Points The EVB is provided with the test points and pin names listed in the table below. Test point/ Pin name Signal Comment (expected waveforms or voltage levels on test points) RSET Switch Frequency Setting Switch Frequency Setting. Connect a resistor from RSET to GND. RRSET = 30kΩ will set f SW = 350kHz. ISW Switch Current Sense External MOSFET Switch Current Sense. Connect the current sense resistor between external N-MOSFET switch and the ground. ISP LED Current Sense LED Current Sense Amplifier Positive Input with Common Mode up to 90V. ISN LED Current Sense LED Current Sense Amplifier Negative Input. Voltage threshold between ISP and ISN is 190mV with common mode voltage up to 90V. VC Compensation PWM Control Loop Compensation. ACTL Analog Dimming Control Analog Dimming Control. The effective programming voltage range of the pin is between 0.2V and 1.2V. DCTL PWM dimming By adding a 0.47µF filtering capacitor on ACTL pin, the PWM dimming signal on DCTL pin can be averaged and converted into analog dimming signal on the ACTL pin. SS Soft-Start Soft-Start Time Setting. A capacitor of at least 10nF is required for proper soft-start. EN Enable Control Enable Control Input (Active High). When this pin voltage is low, the chip is in shutdown mode. OVP Over-Voltage Over-Voltage Protection. The PWM converter turns off when the voltage of the pin goes to higher than 1.18V. VCC Internal Driver voltage Power Supply of the Chip. For good bypass, a low ESR capacitor is required. EVB_RT8494GS-00 December 2015 3 http://www.richtek.com RT8494GS Evaluation Board your power partner. Test point/ Pin name Signal Comment (expected waveforms or voltage levels on test points) GND Ground Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND for Maximum Power Dissipation. GBIAS Gate Driver Bias Internal Gate Driver Bias. A good bypass capacitor is required. GATE Switch Gate Driver External MOSFET Switch Gate Driver Output. Power-up & Measurement Procedure 1. Connect input power (4.5V < VIN < 36V) to VIN test pin. 2. ACTL to 2V, see SW switch is working. 3. Observe the output voltage and output current is correct. Output Over-Voltage Setting The RT8494 is equipped with an Over-Voltage Protection (OVP) function. When the voltage at OVP pin exceeds a threshold of approximately 1.18V, the power switch is turned off. The power switch can be turned on again once the voltage at OVP pin drops below 1.18V. For the Boost and Buck-Boost application, the output voltage could be clamped at a certain voltage level. The OVP voltage can be set by the following equation : VOUT, OVP = 1.18 × (1 + R1 ) R2 LED Current Setting The LED current is programmed by placing an appropriate value current sense resistor between the ISP and ISN pins. Typically, sensing of the current should be done at the top of the LED string. The ACTL pin should be tied to a voltage higher than 1.2V to get the full-scale 190mV (typical) threshold across the sense resistor. The ACTL pin can also be used to dim the LED current to zero, although relative accuracy decreases with the decreasing voltage sense threshold. When the ACTL pin voltage is less than 1.2V, the LED current is : ILED = (VACTL - 0.2) × 0.19 RSENSE EVB_RT8494GS-00 December 2015 4 http://www.richtek.com RT8494GS Evaluation Board your power partner. Schematic, Bill of Materials & Board Layout EVB Schematic Diagram EVB_RT8494GS-00 December 2015 5 http://www.richtek.com RT8494GS Evaluation Board your power partner. Bill of Materials Reference Qty Part Number Description Package Manufacture U1 1 RT8494GS LED Driver Controller SOP-14 RICHTEK C1, C4 2 0603B472K500 4.7µF/50V C-1210/2.159 WALSIN C2, C3 2 C1608X7R1C474K 0.47µF C0603 TDK C5 1 C1608COG1H332J 3.3nF C0603 TDK C6 1 0603B103K500 10nF C0603 WALSIN C8, C10 2 C3225Y5V1H106Z 10µF/50V C-1210/3.048 TDK C9 1 0603B472K500 4.7µF/50V C-1210/2.159 WALSIN D1 1 SR26, 2A, 60V SMC PANJIT VOUT1, GND, VIN, VOUT2, 6 GP SIP-1P-GP L1 1 22µH L-SH8018 美磊/乾坤 Q2 1 FTU36N06N TO-252-123 營格 R19 1 470mΩ RC-1A Viking R10 1 30mΩ RC-1A Viking R13 1 WR06X3002F 30k R0603 WALSIN R2, R14 2 WR06X1002F 10k R0603 WALSIN R12 1 WR06X4303F 430k R0603 WALSIN R5,R6 2 WR06X1003F 100k R0603 WALSIN R3, R7, R9, R16, R27 5 EVB_RT8494GS-00 December 2015 0 (short) 6 http://www.richtek.com RT8494GS Evaluation Board your power partner. PCB Layout Top View Bottom View EVB_RT8494GS-00 December 2015 7 http://www.richtek.com RT8494GS Evaluation Board your power partner. More Information For more information, please find the related datasheet or application notes from Richtek website http://www.richtek.com. Important Notice for Richtek Evaluation Board THIS DOCUMENT IS FOR REFERENCE ONLY, NOTHING CONTAINED IN THIS DOCUMENT SHALL BE CONSTRUED AS RICHTEK’S WARRANTY, EXPRESS OR IMPLIED, UNDER CONTRACT, TORT OR STATUTORY, WITH RESPECT TO THE PRESENTATION HEREIN. IN NO EVENT SHALL RICHTEK BE LIABLE T O BUYER OR USER FOR ANY AND ALL DAMAGES INCLUDING WITHOUT LIMITATION TO DIRECT, INDIRECT, SPECIAL, PUNITIVE OR CONSEQUENTIAL DAMAGES. EVB_RT8494GS-00 December 2015 8 http://www.richtek.com