RT8509AGQW

® RT8509A 4.5A Step-Up DC/DC Converter General Description Features The RT8509A is a high performance switching Boost converter that provides a regulated supply voltage for active matrix thin film transistor (TFT) liquid crystal displays (LCDs).  90% Efficiency  Adjustable Output Up to 24V 2.8V to 14V Input Supply Voltage Input Supply Under-Voltage Lockout Fixed 1.2MHz Switching Frequency Adjustable Soft-Start VOUT Over-Voltage Protection Over-Temperature Protection Thin 12-Lead WDFN Package RoHS Compliant and Halogen Free    The RT8509A 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 RT8509A 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 (min.). Other features include adjustable soft-start, over-voltage protection, and over-temperature protection.  Applications  GIP TFT-LCD Panels Ordering Information The RT8509A is available in the WDFN-12L 5x5 package. RT8509A Package Type QW : WDFN-12L 5x5 (W-Type) Marking Information RT8509AGQW : Product Number RT8509A GQW YMDNN Lead Plating System G : Green (Halogen Free and Pb Free) YMDNN : Date Code Note : Richtek products are :  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit D1 L1 VIN CIN VOUT R4 COUT LX VIN C2 R1 VOUT C3 RT8509A R2 FB Enable EN CSS SS GND COMP R3 C1 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8509A Pin Configurations (TOP VIEW) COMP FB EN GND GND GND 1 12 2 11 3 4 5 6 10 GND 9 13 8 7 SS VIN VOUT GND LX LX WDFN-12L 5x5 Functional Pin Description Pin No. Pin Name Pin Function COMP Compensation Node for Error Amplifier. Connect a series RC from COMP to ground. 2 FB Feedback Voltage Input. 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 Enable Control Input. Drive EN low to turn off the Boost. 1 4, 5, 6, 9, GND 13 (Exposed Pad) Ground. The Exposed Pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 7, 8 LX Switch Node. LX is the Drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and minimize the trace area for lower EMI. 10 VOUT Over-Voltage Protection Input for Boost Converter. Bypass VOUT with a minimum 1F ceramic capacitor directly to GND. 11 VIN Supply Voltage Input. Bypass VIN with a minimum 1μF ceramic capacitor directly to GND. 12 SS Soft-Start Time Setting. Connect a soft-start capacitor (CSS) to this pin. The soft-start capacitor is charged with a constant current of 5A. The soft-start capacitor is discharged to ground when EN is low. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8509A-00 November 2013 RT8509A Function Block Diagram LX OTP VIN EN COMP Error Amplifier Summing Comparator + 1.25V + FB VOUT Protection OVP Oscillator VDD Slope Compensation Clock Soft Start SS LX Control and Driver Logic GND Current Sense Operation The RT8509A is a high-performance step-up DC/DC converter that provides a regulated and high precision supply voltage. It incorporates current mode, fixedfrequency, pulse-width modulation (PWM) circuitry with a built-in N-Channel power MOSFET to achieve high efficiency and fast transient response. The device features an adjustable soft start time using an external soft-start capacitor to reduce in-rush current. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8509A Absolute Maximum Ratings          (Note 1) LX to GND ------------------------------------------------------------------------------------------------------------------- −0.3V to 28V VIN, EN to GND ------------------------------------------------------------------------------------------------------------ −0.3V to 16.5V Other Pins ------------------------------------------------------------------------------------------------------------------- −0.3V to 6.5V Power Dissipation, PD @ TA = 25°C WDFN-12L 5x5 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-12L 5x5, θJA ------------------------------------------------------------------------------------------------------WDFN-12L 5x5, θJC ------------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10sec.) -------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- Recommended Operating Conditions   3.38W 29.5°C/W 7.5°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 2.8 -- 14 V -- -- 24 V -- 2.5 3 V -- 200 -- mV VFB = 1.3V, LX Not Switching VFB = 1V, LX Switching -- 1 -- -- 5 -- Temperature Rising -- 155 -- C -- 10 -- C -- 26 -- V Supply Current Input Voltage Range VIN Output Voltage Range VOUT Under Voltage Lockout Threshold VUVLO UVLO Hysteresis VUVLO VIN Quiescent Current IQ Thermal Shutdown Threshold TSD Thermal Shutdown TSD Hysteresis VOUT Over Voltage Threshold VIN Rising VOUT Rising mA Oscillator Oscillator Frequency fOSC 1000 1200 1500 kHz Maximum Duty Cycle DMAX -- 90 -- % FB Regulation Voltage VREF 1.2312 1.25 1.2688 V FB Input Bias Current IFB -- -- 100 nA -- 0.05 0.2 %/V Error Amplifier FB Line Regulation Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8509A-00 November 2013 RT8509A Parameter Symbol Test Conditions Min Typ Max Unit Transconductance gm I = ±2.5μA at VCOMP = 1V -- 100 -- A/V Voltage Gain AV FB to COMP -- 700 -- V/V 4.5 5 -- A -- 100 250 m -- 30 45 A -- 0.25 -- V/A -- 5 -- A N-MOSFET Current Limit ILIM On-Resistance RDS(ON) Leakage Current Current Sense Transresistance Soft-Start ILEAK 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 © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8509A Typical Application Circuit VIN 12V L1 4.7µH CIN 10µF x 3 D1 7, 8 LX 10 VOUT R4 10 11 VIN RT8509A C2 1µF Enable 3 EN 4, 5, 6, 9, GND 13 (Exposed Pad) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 FB SS COMP 2 R1 134k C3 1µF R2 10k CSS 33nF 12 1 VOUT 18V COUT 10µF x 4 R3 56k C1 1nF is a registered trademark of Richtek Technology Corporation. DS8509A-00 November 2013 RT8509A Typical Operating Characteristics Boost Efficiency vs. Load Current Boost Efficiency vs. Load Current 100 100 90 VIN = 3.3V 80 70 60 Boost Efficiency (%) Boost Efficiency (%) VIN = 5V VOUT = 13.5V, fOSC = 1.2MHz 50 0 0.1 0.2 0.3 0.4 VIN = 14V VIN = 12V VIN = 10V 90 80 70 60 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 8 Boost Current Limit (A) Boost Reference Voltage (V) 0.9 1.4 1.3 1.2 1.1 1 7 6 5 4 3 2 4 6 8 10 12 Input Voltage (V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 14 2 4 6 8 10 12 14 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8509A Application Information The RT8509A is a high performance step-up DC/DC converter that provides a regulated supply voltage for panel source driver ICs. The RT8509A 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 internal driver power is supplied from the VOUT pin and that will increase efficiency when low input voltage condition. The following content contains detailed description and information for component selection. Boost Regulator The RT8509A is a current mode Boost converter integrated with a 24V/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 the 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. The Boost minimum gain ratio depends on minimum on-time. It's suggested that VOUT higher than 1.2 x VIN for better performance. Soft-Start The RT8509A 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. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 If CSS < 220pF, the internal soft-start function will be turned on and period time is approximately 1ms. 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 RT8509A Boost converter has over-current protection to limit the peak inductor current. It prevents the inductor and diode from damage due to large current. 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 RT8509A 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. is a registered trademark of Richtek Technology Corporation. DS8509A-00 November 2013 RT8509A 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 as an example, the inductor ripple current can be calculated according to the following equations : IIN(MAX) = VOUT x IOUT(MAX)  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 : Q 1  1 1    x  IIN  IL  IOUT    IIN  IL  IOUT   2  2 2    VIN 1  COUT x VOUT1 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 VOUT1   x COUT x fOSC  x (VIN )2 x(VOUT  VIN ) 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 VOUT  IIN x ESR   x COUT x fOSC 0.4 x (VOUT )2 xIOUT(MAX) x fOSC The output capacitor, COUT, should be selected accordingly. 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 : L 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 : 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 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 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. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8509A 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. Maximum Power Dissipation (W)1 4.0 Thermal 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 : Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) PD(MAX) = (TJ(MAX) − TA) / θJA Figure 2. Derating Curve of Maximum Power Dissipation where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. Layout Considerations For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-12L 5x5 packages, the thermal resistance, θJA, is 29.5°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 :  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.  The feedback voltage divider resistors must be near the feedback pin. The divider center trace must be shorter and the trace must be kept away from any switching nodes. PD(MAX) = (125°C − 25°C) / (29.5°C/W) = 3.38W for WDFN-12L 5x5 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. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 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.  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. is a registered trademark of Richtek Technology Corporation. DS8509A-00 November 2013 RT8509A The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. Locate the C2 as close to the VIN pin as possible. GND GND C1 R3 R1 R2 VOUT COMP 1 12 SS FB 2 11 VIN EN 3 GND 4 GND GND 13 GND VIN C2 R4 Place the power components as close as possible. The traces should be wide and short especially for the highcurrent loop. 10 VOUT 9 GND 5 8 LX 6 7 LX D1 VOUT COUT L1 The feedback voltage-divider resistors must near the feedback pin. The divider center trace must be shorter and avoid the trace near any switching nodes. GND CIN VIN + More GND via and layout area for better thermal performance. The switching trace should be wide and short especially for the high-current loop. VIN Figure 3. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8509A-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8509A Outline Dimension 2 1 2 1 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 0.200 0.300 0.008 0.012 D 4.900 5.100 0.193 0.201 D2 4.250 4.350 0.167 0.171 E 4.900 5.100 0.193 0.201 E2 3.650 3.750 0.144 0.148 0.800 e L 0.350 0.031 0.450 0.014 0.018 W-Type 12L DFN 5x5 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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. www.richtek.com 12 DS8509A-00 November 2013