® RT9297 3A High Performance Step-Up DC/DC Converter General Description Features The RT9297 includes a high performance step-up DC/DC converter that provides a regulated supply voltage for activematrix thin-film transistor (TFT) liquid-crystal displays (LCDs). z High Efficiency Up to 90% z Adjustable Output Voltage : VDD to 24V Wide Input Supply Voltage : 2.6V to 5.5V Input Under Voltage Lockout Pin-Programmable Switching Frequency 640kHz/ 1.2MHz Programmable Soft-Start Small 10-Lead WDFN Package RoHS Compliant and Halogen Free z z z The Boost Converter 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. z z z The RT9297 is available in a WDFN -10L 3x3 package. Applications Ordering Information z RT9297 z Package Type QW : WDFN-10L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) z Notebook Computer Displays LCD Monitor Panels LCD TV Panels Pin Configurations Richtek products are : ` COMP FB EN GND GND RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. 1 2 3 4 5 GND (TOP VIEW) Note : 11 10 9 8 7 6 SS FREQ VDD LX LX WDFN-10L 3x3 Marking Information EZ= : Product Code EZ=YM DNN YMDNN : Date Code Typical Application Circuit L1 VDD 2.6V to 5.5V C1 R3 C3 June 2012 VAVDD RT9297 6, 7 8 VDD LX 9 2 FREQ FB 3 EN CSS 1 COMP 10 SS GND 4, 5, 11 (Exposed Pad) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9297-02 D1 C2 R1 R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9297 Function Block Diagram LX VIN VFB EN 4µA SoftStart Protection SS COMP Error Amplifier - FB 1.24V + Summing Comparator + Control and Driver Logic Clock FREQ VDD Oscillator Slope Compensation LX GND Current Sense 4µA Functional Pin Description Pin No. Pin Name Pin Function COMP Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. 2 FB Feedback. The feedback regulation voltage is 1.24V nominal. Connect an external resistive voltage-divider between the step-up regulator’s output (VAVDD) 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 Converter. GND 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 VDD Supply Pin. Bypass VDD with a minimum 1μF ceramic capacitor directly to GND. 9 FREQ Frequency-Select Input. When FREQ is low, the oscillator frequency will be set to 640kHz. When FREQ is high, the frequency will be set to 1.2MHz. This input has a 6μA pull-down current. SS Soft-Start Control. Connect a soft-start capacitor (CSS) to this pin. A 4μA constant current charges the soft-start capacitor. When EN connected to GND, the soft-start capacitor is discharged. When EN connected to VDD high, the soft-start capacitor is charged to VDD. Leave floating for not using soft-start. 1 4, 5 11 (Exposed Pad) 6, 7 10 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9297-02 June 2012 RT9297 Absolute Maximum Ratings z z z z z z z z (Note 1) LX to GND --------------------------------------------------------------------------------------------------------------- −0.3V to 26V Other Pins to GND ---------------------------------------------------------------------------------------------------- −0.3V to 6V Power Dissipation, PD @ TA = 25°C WDFN-10L 3x3 --------------------------------------------------------------------------------------------------------- 1.667W Package Thermal Resistance (Note 2) WDFN-10L 3x3, θJA --------------------------------------------------------------------------------------------------- 60°C/W WDFN-10L 3x3, θJC --------------------------------------------------------------------------------------------------- 8.2°C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C Junction Temperature ------------------------------------------------------------------------------------------------- 150°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------------------------ 2kV MM (Machine Model) ------------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions z z z (Note 4) Supply Input Voltage, VDD ------------------------------------------------------------------------------------------ 2.6V to 5.5V Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VDD = 3.3V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 2.6 -- 5.5 4 -- 5.5 VDD -- 24 V VDD Rising -- 2.4 -- V Hysteresis -- 50 -- mV VFB = 1.3V, LX Not Switching -- 0.5 -- V FB = 1V, LX Switching -- 4 -- EN = GND -- 0.1 10 FREQ = GND 500 640 750 FREQ = VlN 1000 1240 1500 -- 90 -- % Supply Current Input Voltage Range VDD Output Voltage Range VAVDD Under-Voltage Lockout VUVLO Threshold Quiescent Current IQ Shutdown Current ISHDN VAVDD < 18V 18V < VAVDD < 24V V mA μA Oscillator Oscillator Frequency fOSC Maximum Duty Cycle kHz Error Amplifier Feedback Regulation Voltage VFB 1.22 1.24 1.26 V Feedback Input Bias Current I FB -- 125 250 nA Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9297-02 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9297 Parameter Symbol Test Conditions Feedback Line Regulation Min Typ Max Unit -- 0.05 0.2 %/V Transconductance gm ΔI = ±2.5μA at COMP = 1V -- 135 -- μA/V Voltage Gain Av FB to COMP -- 700 -- V/V N- MOSFET Current Limit ILIM 3 3.8 5 A On-Resistance R DS(ON) -- 125 250 mΩ Leakage Current ILEAK -- 30 45 μA Current-Sense Transresistance R CS -- 0.25 -- V/A ISS -- 4 -- μA EN, FREQ Input Low Voltage VIL -- -- 0.3 x V DD V EN, FREQ Input High Voltage VIH 0.7 x VDD -- -- V EN, FREQ Input Hysteresis -- 0.1 x V DD -- V FREQ Pull-down Current -- 6 -- μA -- 0.001 1 μA VLX = 24V Soft-Start Charge Current Control Inputs EN Input Current IEN EN = GND 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. DS9297-02 June 2012 RT9297 Typical Operating Characteristics Efficiency vs. Load Current Efficiency vs. Load Current 100 100 90 90 VDD = 5V 70 80 VDD = 3.3V Efficiency (%) Efficiency (%) 80 VDD = 5V 60 50 40 30 VDD = 3.3V 70 60 50 40 30 20 20 10 10 VAVDD = 13.6V, f = 1.2MHz VAVDD = 13.6V, f = 640kHz 0 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 0.4 0.05 0.1 13.69 13.69 13.68 13.68 13.67 13.66 VDD = 5V 13.65 13.64 VDD = 3.3V 0.25 0.3 0.35 0.4 13.67 13.66 VDD = 5V 13.65 13.64 VDD = 3.3V 13.63 13.62 13.62 13.61 13.61 VAVDD = 13.6V, f = 1.2MHz VAVDD = 13.6V, f = 640kHz 13.60 13.60 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 0.4 0.05 13.65 13.65 13.64 13.64 13.63 IAVDD = 0mA IAVDD = 100mA IAVDD = 200mA IAVDD = 300mA IAVDD = 400mA 13.60 13.59 Output Voltage (V) 13.66 13.61 0.15 0.2 0.25 0.3 0.35 0.4 Output Voltage vs. Input Voltage Output Voltage vs. Input Voltage 13.66 13.62 0.1 Load Current (A) Load Current (A) Output Voltage (V) 0.2 Output Voltage vs. Load Current 13.70 Output Voltage (V) Output Voltage (V) Output Voltage vs. Load Current 13.70 13.63 0.15 Load Current (A) Load Current (A) 13.63 13.62 IAVDD = 0mA IAVDD = 100mA IAVDD = 200mA IAVDD = 300mA IAVDD = 400mA 13.61 13.60 13.59 f = 1.2MHz 13.58 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9297-02 June 2012 5.5 f = 640kHz 13.58 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9297 Reference Voltage vs. Temperature Switching Frequency vs. Temperature 1.260 1.40 1.256 Reference Voltage (V) Switch Frequency (MHz 1.35 1.30 1.25 1.20 1.15 1.10 1.05 VDD = 3.3V 1.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 1.252 1.248 1.244 1.240 1.236 1.232 1.228 1.224 VDD = 3.3V, f = 1.2MkHz 1.220 -40 -25 -10 35 50 65 Temperature (°C) Start Up Start Up VAVDD (5V/Div) VDD (2V/Div) VAVDD (5V/Div) VLX (10V/Div) VLX (10V/Div) VDD = 3.3V, VAVDD = 13.6V f = 1.2MHz, IAVDD = 300mA I VDD (1A/Div) 80 95 110 125 VDD = 5V, VAVDD = 13.6V f = 1.2MHz, IAVDD = 300mA Time (2.5ms/Div) Time (2.5ms/Div) Load Transient Response Load Transient Response VDD = 5V, VAVDD = 13.6V, f = 1.2MHz VDD = 3.3V, VAVDD = 13.6V, f = 1.2MHz VAVDD (500mV/Div) VAVDD (500mV/Div) IAVDD (200mA/Div) IAVDD (500mA/Div) Time (100μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 20 Temperature (°C) VDD (2V/Div) I VDD (1A/Div) 5 Time (100μs/Div) is a registered trademark of Richtek Technology Corporation. DS9297-02 June 2012 RT9297 Application Information The RT9297 contains a high performance boost regulator to generate voltage for the panel source driver ICs. The following content contains the detailed description and the information of component selection. Boost Regulator The boost regulator is a high efficiency current-mode PWM architecture with 640K / 1.2MHz operation frequency. It performs fast transient responses to generate source driver supplies for TFT LCD display. The high operation frequency allows smaller components used to minimize the thickness of the LCD panel. The output voltage setting can be achieved by setting the resistive voltage-divider sensing at 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. Loop Compensation The voltage feedback loop can be compensated with an external compensation network consisted of RCOMP and CCOMP. Choose RCOMP to set high frequency integrator gain for fast transient response and CCOMP to set the integrator zero to maintain loop stability. For typical application VDD = 3.3V , VAVDD = 13.6V , C4 = 4.7μF x 3 , L = 3.6μH, the recommended value for compensation is as below : RCOMP = 56kΩ, CCOMP = 330pF. Over Current Protection The RT9297 boost converter has over-current protection to limit peak inductor current. It prevents large current from damaging the inductor and diode. During the ONtime, 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 there should is also affected by the input voltage, duty cycle and inductor value. Soft-Start The RT9297 provides soft-start function to minimize the inrush current. When power on, an internal constant current charges an external capacitor. The rising voltage rate on the COMP pin is limited during the charging period and the inductor peak current will also be limited at the same time. When power off, the external capacitor will be discharged for next soft start time. The soft-start function is implemented by the external capacitor with a 4μA constant current charging to the softstart capacitor. Therefore, the capacitor should be large enough for output voltage regulation. Typical value for softstart capacitor range is 33nF. The available soft-start capacitor range is from 10nF to 100nF. Output Voltage Setting The regulated output voltage is shown as following equation : ⎛ R ⎞ VAVDD = 1.24V x ⎜ 1+ 1 ⎟ ⎝ R2 ⎠ The recommended value for R2 should be up to 10kΩ without some sacrificing. To place the resistor divider as close as possible to the chip can reduce noise sensitivity. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9297-02 June 2012 Over Temperature Protection The RT9297 boost converter has thermal protection function to prevent the chip from overheating. When the junction temperature exceeds 155°C, it will shut down the device. Once the device cools down by approximately 30°C, it will start to operate normally. For continuous operation, do not operate over the maximum junction temperature rating 125°C. Inductor Selection The inductance depends on the maximum input current. The inductor current ripple is 20% to 40% of maximum input current that is a general rule. Assume, choose 40% as the criterion then IVDD(MAX) = VAVDD x IAVDD(MAX) η x VDD IRIPPLE = 0.4 x IVDD(MAX) Where η is the efficiency, IIN(MAX) is the maximum input current, IRIPPLE is the inductor current ripple. Beside, the input peak current is maximum input current plus half of inductor current ripple. is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9297 IPEAK = 1.2 x IVDD(MAX) Note that the saturated current of inductor must be greater than IPEAK. The inductance can be eventually determined as follow equation : ΔIL Input Current Inductor Current 2 L= η x ( VDD ) x ( VAVDD -VDD ) 2 0.4 x ( VAVDD ) x I AVDD(MAX) x fOSC Output Current Time Where fOSC is the switching frequency. To consider the system performance, a shielded inductor is preferred to avoid EMI issue. (1-D)TS Output Ripple Voltage (ac) Time ΔVOUT1 Diode Selection Schottky diode is a good choice for an asynchronous Boost converter due to the small forward voltage. However, power dissipation, reverse voltage rating and pulsating peak current are the important parameters for Schottky diode selection. It is recommended to choose a suitable diode whose reverse voltage rating is greater than the maximum output voltage. Capacitor Selection Output ripple voltage is an important index for estimating the performance. This portion consists of two parts, one is the product of input current and ESR of output capacitor, another part is formed by charging and discharging process of output capacitor. Refer to Figure 1, evaluate DVOUT1 by ideal energy equalization. According to the definition of Q, the Q value can be calculated as following equation : ⎡ ⎤ Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥ 2 ⎣⎝ 2 2 ⎠ ⎝ ⎠⎦ V × IN × 1 = COUT × ΔVOUT1 VOUT fSW where fSW is the switching frequency, and ΔIL is the inductor ripple current. Move COUT to the left side to estimate the value of ΔVOUT1 as the following equation : ΔVOUT1 = D × IOUT η × COUT × fSW Finally, by taking ESR into consideration, the overall output ripple voltage can be determined as the following equation : ΔVOUT = IIN × ESR + D × IOUT η × COUT × fSW Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 Figure 1. The Output Ripple Voltage without the Contribution of ESR 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 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 must be greater than the maximum input voltage. Thermal Considerations For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = (TJ(MAX) − TA ) / θJA Where T J(MAX) is the maximum operation junction temperature 125°C, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification, where TJ(MAX) is the maximum junction temperature of the die (125°C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance θJA is layout is a registered trademark of Richtek Technology Corporation. DS9297-02 June 2012 RT9297 dependent. For WDFN-10L 3x3 packages, the thermal resistance θJA is 60°C/W on the standard JEDEC 51-7 four layers thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for WDFN-10L 3x3 package The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA . The Figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Maximum Power Dissipation (W) 1.8 Four Layers PCB Layout Considerations 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. ` 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 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. ` 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. 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 20 40 60 80 100 120 140 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation C3 GND R3 R2 COMP FB EN GND GND 1 2 3 4 5 GND The compensation circuit should be kept away from the power loops and be shielded with a ground trace to prevent any noise coupling. 11 10 9 8 7 6 SS FREQ VDD LX LX For good regulation place the power components as close as possible. The traces should be wide and short especially for the high-current output loop. L1 + VIN D1 R1 AVDD 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. C2 C1 GND Figure 3. PCB Layout Guide Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9297-02 June 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9297 Outline Dimension D2 D L E E2 1 SEE DETAIL A 2 e A A1 1 2 1 b DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol 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. www.richtek.com 10 DS9297-02 June 2012