® RT8509 3A, 14V Step-Up DC/DC Converter General Description Features The RT8509 is a high performance switching boost converter that provides a regulated supply voltage for active matrix thin film transistor (TFT) liquid crystal displays (LCDs). z 90% Efficiency z Adjustable Output Up to 24V 2.8V to 14V Input Supply Voltage Input Supply Under Voltage Lockout Fixed 1.2MHz Switching Frequency Programmable Soft-Start VOUT Over Voltage Protection Over Temperature Protection Thin 10-Lead WDFN Package RoHS Compliant and Halogen Free z z z The RT8509 incorporates current mode, fixed-frequency, pulse width modulation (PWM) circuitry with a built in N-MOSFET to achieve high efficiency and fast transient response. z z z z The RT8509 has a wide input voltage range from 2.8V to 14V. In addition, the output voltage can be adjusted up to 24V via an external resistive voltage divider. The maximum peak current is limited to 4.5A (typ.). Other features include programmable soft-start, over voltage protection, and over temperature protection. z Applications z GIP TFT LCD Panels Pin Configurations The RT8509 is available in a WDFN-10L 3x3 package. Ordering Information COMP FB EN GND GND RT8509 Package Type QW : WDFN-10L 3x3 (W-Type) Note : Lead Plating System G : Green (Halogen Free and Pb Free) RoHS compliant and compatible with the current require- 7 6 11 H4= : Product Code H4=YM DNN Suitable for use in SnPb or Pb-free soldering processes. Typical Application Circuit VIN 12V CIN 10µF x 2 Chip Enable L1 4.7µH C2 1µF VOUT 6, 7 LX 8 VSUP R4 10 9 VIN 4, 5, 11 (Exposed Pad) YMDNN : Date Code D1 RT8509 3 EN GND Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8509-01 March 2012 8 SS VIN VSUP LX LX Marking Information ments of IPC/JEDEC J-STD-020. ` 4 5 10 9 WDFN-10L 3x3 Richtek products are : ` 1 2 3 GND (TOP VIEW) FB SS COMP C3 1µF 2 R2 10k CSS 33nF 10 1 R1 134k 18V COUT 4.7µF x 3 R3 56k C1 1nF is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8509 Functional Pin Description Pin No. 1 Pin Name Pin Function COMP Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. 2 FB Feedback. The FB regulation voltage is 1.25V nominal. Connect an external resistive voltage divider between the step-up regulator’s output (VOUT) and GND, with the center tap connected to FB. Place the divider close to the IC and minimize the trace area to reduce noise coupling. 3 EN Chip Enable. Drive EN low to turn off the Boost. 4, 5, GND 11 (Exposed Pad) Ground. The Exposed Pad must be soldered to a large PCB and connected to GND for maximum power dissipation. LX Switch. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and minimize the trace area for lower EMI. 8 VSUP Boost Converter Over Voltage Protection Input. Bypass VSUP with a minimum 1μF ceramic capacitor directly to GND. 9 VIN Supply Input . Bypass VIN with a minimum 1μF ceramic capacitor directly to GND. 10 SS Soft-Start Control. Connect a soft-start capacitor (CSS) to this pin. The soft-start capacitor is charged with a constant current of 5μA. The soft-start capacitor is discharged to ground when EN is low. 6, 7 Function Block Diagram LX OTP VIN EN COMP Error Amplifier Summing Comparator + 1.25V + FB VSUP OVP Oscillator VDD Slope Compensation Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 Protection Clock Soft Start SS LX Control and Driver Logic GND Current Sense is a registered trademark of Richtek Technology Corporation. DS8509-01 March 2012 RT8509 Absolute Maximum Ratings z z z z z z z z z (Note 1) LX, VSUP to GND --------------------------------------------------------------------------------------------------------- −0.3V to 28V VIN, EN to GND ------------------------------------------------------------------------------------------------------------ −0.3V to 16.5V Other Pins to GND -------------------------------------------------------------------------------------------------------- −0.3V to 6.5V Power Dissipation, PD @ TA = 25°C WDFN-10L 3x3 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-10L 3x3, θJA ------------------------------------------------------------------------------------------------------WDFN-10L 3x3, θJC ------------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10sec.) -------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- Recommended Operating Conditions z z 1.429W 70°C/W 8.2°C/W 150°C −65°C to 150°C 260°C 2kV 200V (Note 4) Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VIN = 3.3V, VOUT = 10V, TA =25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Current Input Voltage Range VIN 2.8 -- 14 V Output Voltage Range Under Voltage Lockout Threshold UVLO Hysteresis VOUT -- -- 24 V -- 2.5 3 V -- 200 -- mV VIN Quiescent Current IQ VUVLO VIN Rising ΔVUVLO Thermal Shutdown Threshold TSD Thermal Shutdown ΔTSD Hysteresis VSUP Over Voltage Threshold Oscillator VFB = 1.3V, LX Not Switching VFB = 1V, LX Switching -- 1 -- -- 5 -- Temperature Rising -- 155 -- °C -- 10 -- °C -- 26 -- V VSUP Rising mA Oscillator Frequency f OSC 1000 1200 1500 kHz Maximum Duty Cycle D MAX -- 90 -- % FB Regulation Voltage VREF -- 1.25 -- V FB Input Bias Current IFB -- -- 100 nA -- 0.05 0.2 %/V Error Amplifier FB Line Regulation Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8509-01 March 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8509 Parameter Symbol Test Conditions Min Typ Max Unit Transconductance gm ΔI = ±2.5μA at VCOMP = 1V -- 100 -- μA/V Voltage Gain AV FB to COMP -- 700 -- V/V N-MOSFET Current Limit ILIM 3 3.5 -- A On-Resistance RDS(ON) -- 100 250 mΩ Leakage Current Current Sense Transresistance Soft-Start ILEAK -- 30 45 μA -- 0.25 -- V/A -- 5 -- μA VLX = 24V RCS Charge Current Control Inputs EN Input Voltage Logic-High VIH 1.5 -- -- Logic-Low VIL -- -- 0.5 V Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8509-01 March 2012 RT8509 Typical Operating Characteristics Boost Efficiency vs. Load Current Boost Efficiency vs. Load Current 100 100 90 VIN = 3.3V 80 70 60 80 70 60 VOUT = 13.5V, fOSC = 1.2MHz 50 0 0.1 0.2 0.3 0.4 VIN = 14V VIN = 12V VIN = 10V 90 Boost Efficiency (%) Boost Efficiency (%) VIN = 5V VOUT = 18V, fOSC = 1.2MHz 50 0.5 0 0.3 0.6 Boost Reference Voltage vs. Temperature 1.5 Boost Frequency vs. Temperature 1400 Boost Frequency (kHz) 1.5 Boost Reference Voltage (V) 1.2 Load Current (A) Load Current (A) 1.4 1.3 1.2 1.1 VIN = 3.3V 1 -50 -25 0 25 50 75 100 1300 1200 1100 1000 VIN = 3.3V 900 -50 125 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) Boost Current Limit vs. Input Voltage Boost Reference Voltage vs. Input Voltage 1.5 7 1.4 6 Boost Current Limit (A) Boost Reference Voltage (V) 0.9 1.3 1.2 1.1 1 5 4 3 2 2 4 6 8 10 12 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8509-01 March 2012 14 2 4 6 8 10 12 14 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8509 Application Information The RT8509 is a high performance step-up DC/DC converter that provides a regulated supply voltage for panel source driver ICs. The RT8509 incorporates current mode, fixed frequency, Pulse Width Modulation (PWM) circuitry with a built in N-MOSFET to achieve high efficiency and fast transient response. The following content contains detailed description and information for component selection. Boost Regulator The RT8509 is a current mode boost converter integrated with a 24V/3.5A power switch, covering a wide VIN range from 2.8V to 14V. It performs fast transient responses to generate source driver supplies for TFT LCD display. The high operation frequency allows use of smaller components to minimize the thickness of the LCD panel. The output voltage can be adjusted by setting the resistive voltage-divider sensing at the FB pin. The error amplifier varies the COMP voltage by sensing the FB pin to regulate the output voltage. For better stability, the slope compensation signal summed with the current sense signal will be compared with the COMP voltage to determine the current trip point and duty cycle. Soft-Start The RT8509 provides soft-start function to minimize the inrush current. When powered on, an internal constant current charges an external capacitor. The rising voltage rate on the COMP pin is limited from VSS = 0V to 1.24V and the inductor peak current will also be limited at the same time. When powered off, the external capacitor will be discharged until the next soft-start time. The soft-start function is implemented by the external capacitor with a 5μA constant current charging to the softstart capacitor. Therefore, the capacitor should be large enough for output voltage regulation. A typical value for soft-start capacitor is 33nF. The available soft-start capacitor range is from 10nF to 100nF. If CSS < 220pF, the internal soft-start function will be turned on and period time is approximately 1ms. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 Output Voltage Setting The regulated output voltage is shown as the following equation : ⎛ R1 ⎞ VOUT = VREF x ⎜ 1+ ⎟ , where VREF = 1.25V (typ.) ⎝ R2 ⎠ The recommended value for R2 should be at least 10kΩ without some sacrificing. Place the resistive voltage divider as close as possible to the chip to reduce noise sensitivity. Loop Compensation The voltage feedback loop can be compensated with an external compensation network consisting of R3. Choose R3 to set high frequency integrator gain for fast transient response and C1 to set the integrator zero to maintain loop stability. For typical application, V IN = 5V, VOUT = 13.6V, COUT = 4.7μF x 3, L1 = 4.7μH, while the recommended value for compensation is as follows : R3 = 56kΩ, C1 = 1nF. Over Current Protection The RT8509 boost converter has over current protection to limit the peak inductor current. It prevents large current from damaging the inductor and diode. During the On-time, once the inductor current exceeds the current limit, the internal LX switch turns off immediately and shortens the duty cycle. Therefore, the output voltage drops if the over current condition occurs. The current limit is also affected by the input voltage, duty cycle, and inductor value. Over Temperature Protection The RT8509 boost converter has thermal protection function to prevent the chip from overheating. When the junction temperature exceeds 155°C, the function shuts down the device. Once the device cools down by approximately 10°C, it will automatically restart to normal operation. To guarantee continuous operation, do not operate over the maximum junction temperature rating of 125°C. Inductor Selection The inductance depends on the maximum input current. As a general rule, the inductor ripple current range is 20% to 40% of the maximum input current. If 40% is selected is a registered trademark of Richtek Technology Corporation. DS8509-01 March 2012 RT8509 as an example, the inductor ripple current can be calculated according to the following equations : IIN(MAX) = VOUT x IOUT(MAX) η x VIN IRIPPLE = 0.4 x IIN(MAX) where η is the efficiency of the converter, IIN(MAX) is the maximum input current, and IRIPPLE is the inductor ripple current. The input peak current can then be obtained by adding the maximum input current with half of the inductor ripple current as shown in the following equation : IPEAK = 1.2 x IIN(MAX) Note that the saturated current of the inductor must be greater than IPEAK. The inductance can eventually be determined according to the following equation : η x (VIN )2 x(VOUT − VIN ) L= 0.4 x (VOUT )2 xIOUT(MAX) x fOSC Q= 1 ⎡⎛ 1 1 ⎞ ⎛ ⎞⎤ x ⎜ IIN + ΔIL − IOUT ⎟ + ⎜ IIN − ΔIL − IOUT ⎟ ⎥ 2 ⎢⎣⎝ 2 2 ⎠ ⎝ ⎠⎦ VIN 1 = COUT x ΔVOUT1 x x VOUT fOSC where fOSC is the switching frequency, and ΔIL is the inductor ripple current. Bring COUT to the left side to estimate the value of ΔVOUT1 according to the following equation : D x IOUT ΔVOUT1 = η x COUT x fOSC where D is the duty cycle and η is the boost converter efficiency. Finally, taking ESR into account, the overall output ripple voltage can be determined by the following equation : D x IOUT ΔVOUT = IIN x ESR + η x COUT x fOSC The output capacitor, COUT, should be selected accordingly. where fosc is the switching frequency. For better system performance, a shielded inductor is preferred to avoid EMI problems. ΔIL Input Current Inductor Current Diode Selection Schottky diodes are chosen for their low forward voltage drop and fast switching speed. When selecting a Schottky diode, important parameters such as power dissipation, reverse voltage rating, and pulsating peak current should all be taken into consideration. A suitable Schottky diode's reverse voltage rating must be greater than the maximum output voltage and its average current rating must exceed the average output current. Last of all, the chosen diode should have a sufficiently low leakage current level, since it will increase with temperature. Output Current Time (1-D)TS Output Ripple Voltage (ac) Time ΔVOUT1 Figure 1. The Output Ripple Voltage without the Contribution of ESR Output Capacitor Selection The output ripple voltage is an important index for estimating chip performance. This portion consists of two parts. One is the product of the inductor current with the ESR of the output capacitor, while the other part is formed by the charging and discharging process of the output capacitor. As shown in Figure 1, ΔVOUT1 can be evaluated based on the ideal energy equalization. According to the definition of Q, the Q value can be calculated as the following equation : Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8509-01 March 2012 Input Capacitor Selection Low ESR ceramic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input voltage ripple caused by switching operation. A 10μF capacitor is sufficient for most applications. Nevertheless, this value can be decreased for lower output current requirement. Another consideration is the voltage rating of the input capacitor which must be greater than the maximum input voltage. is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8509 Thermal Considerations Layout Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : For high frequency switching power supplies, the PCB layout is important to get good regulation, high efficiency and stability. The following descriptions are the guidelines for better PCB layout. PD(MAX) = (TJ(MAX) − TA) / θJA ` ` The feedback voltage divider resistors must be near the where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. PD(MAX) = (125°C − 25°C) / (70°C/W) = 1.429W for WDFN-10L 3x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. ` The compensation circuit should be kept away from the power loops and be shielded with a ground trace to prevent any noise coupling. ` Minimize the size of the LX node and keep it wide and shorter. Keep the LX node away from the FB. ` The exposed pad of the chip should be connected to a strong ground plane for maximum thermal consideration. GND C1 R3 R1 R2 1.6 Four Layer PCB VOUT 1.4 Place C2 as close to VIN as possible. The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. COMP FB EN GND GND GND 1 2 3 4 5 The feedback voltage-divider resistors must be near the feedback pin. The divider center trace must be shorter and avoid the trace near any switching nodes. 1.2 1.0 0.8 11 10 9 8 7 6 VIN C2 SS VIN VSUP D1 LX LX L1 VIN R4 VOUT COUT CIN + 70°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : feedback pin. The divider center trace must be shorter and the trace must be kept away from any switching nodes. GND For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-10L 3x3 packages, the thermal resistance, θJA, is Maximum Power Dissipation (W)1 For good regulation, place the power components as close as possible. The traces should be wide and short enough especially for the high current output loop. GND Place the power components as close to the IC as possible. The traces should be wide and short, especially for the high-current loop. 0.6 0.4 Figure 3. PCB Layout Guide 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8509-01 March 2012 RT8509 Outline Dimension D2 D L E E2 1 e SEE DETAIL A b 2 1 2 1 A A1 A3 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 2.300 2.650 0.091 0.104 E 2.950 3.050 0.116 0.120 E2 1.500 1.750 0.059 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 10L DFN 3x3 Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8509-01 March 2012 www.richtek.com 9