RT9277A/B High Performance, Low Noise Boost Converter General Description Features The RT9277A/B is a high performance, low noise, fixed frequency step up DC-DC Converter. The RT9277A/B converters input voltage ranging 2.5V to 5.5V into output voltage up to 16V. Current mode control with external compensation network makes it easy to stabilize the system and keep maximum flexibility. Soft start function minimizes impact on the input power system. Internal power MOSFET with very low RDS(ON) provides high efficiency. z The RT9277A/B automatically transits from PWM to PSM (Pulse Skipping Mode) during light load condition further increasing efficiency. 640kHz and 1.2MHz operation frequency options provide flexibiltity of minimum output inductor size, maximum efficiency and low BOM cost. z The RT9277A/B also provides comprehensive protection functions such as UVLO, OCP and OTP. Ordering Information z z z z z z z 90% Efficiency VIN Operating Range : 2.5V to 5.5V Ω, 16V Internal Power MOSFET 1.6A, 0.2Ω 640kHz and 1.2MHz Operation Frequency External Compensation Network Internal/External Programmable Soft Start Function Small MSOP8 Package OCP and OTP Function are Included RoHS Compliant and 100% Lead (Pb)-Free Applications z TFT LCD panel z OLED Display PCMCIA Cards Portable Device z z Pin Configurations RT9277A/B Package Type F : MSOP-8 Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) (TOP VIEW) COMP FB EN GND Soft Start Function A : Internal B : External Programmable Note : Richtek products are : ` RoHS compliant and compatible with the current require- 1 2 3 4 8 7 6 5 NC FREQ VIN LX RT9277A COMP FB EN GND 1 2 3 4 8 7 6 5 SS FREQ VIN LX ments of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. RT9277B MSOP-8 Marking Information For marking information, contact our sales representative directly or through a RichTek distributor located in your area. DS9277A/B-04 April 2011 www.richtek.com 1 RT9277A/B Typical Application Circuit Chip Enable L1 D1 VOUT + + VIN 2.5V to 5.5V C2 C1 5 LX 6 VIN GND 4 EN 3 7 FREQ FB 2 8 NC COMP 1 R1 R3 C4 RT9277A R2 C3 Figure 1 Chip Enable D1 L1 VOUT + + VIN 2.5V to 5.5V C2 C1 5 LX 6 VIN GND 4 EN 3 7 FREQ FB 2 8 SS COMP 1 R1 R3 C4 CSS RT9277B R2 C3 Figure 2 Table 1. Component Selection FOSC C1 L1 C2 (Hz) (uF) (uH) (uF) 1.2M 10 4.7(TDK SLF6028) 33 (ceramic) R3 (kΩ) 82 C3 (pF) 820 C4 (pF) 10 Symbol (unit) Application 1 VIN (V) 3.3 VOUT (V) 9 Application 2 3.3 12 1.2M 10 4.7(TDK SLF6028) 33 (ceramic) 180 680 22 Application 3 3.3 12 640K 10 10(TDK SLF6028) 33 (ceramic) 120 1200 22 Function Block Diagram LX VIN VFB EN COMP FB 1.24V Error Amplifier + Protection Summing Comparator + Internal Soft-Start Control and Driver Logic Clock VIN LX N GND 5uA FREQ Oscillator Slope Compensation Current Sense RT9277A www.richtek.com 2 DS9277A/B-04 April 2011 RT9277A/B LX VIN VFB EN COMP FB 1.24V 4uA VIN Protection SoftStart Error Amplifier + Summing Comparator + Control and Driver Logic SS LX N Clock GND 5uA FREQ Oscillator Slope Compensation Current Sense RT9277B Operation The RT9277A/B is a high efficiency step-up Boost converter with a fixed-frequency, current-mode PWM architecture. It performs fast transient response and low noise operation with appropriate component selection. The output voltage is regulated through a feedback control consisting of an error amplifier, a summing comparator, and several control signal generators (as shown in function block diagram). The feedback reference voltage is 1.24V. The error amplifier varies the COMP voltage by sensing the FB pin. The slope compensation signal summed with the current -sense signal will be compared with the COMP voltage through the summing comparator to determine the current trip point and duty cycle. When driving light loads, the RT9277A/B will perform the pulse-skipping mode to prevent overcharging the output voltage. In this mode, the switching frequency will be reduced to perform a higher efficiency. When the EN pin is connected to GND, the external capacitor will be discharged to ground for the next time soft-start. Soft-Start Frequency Selection The RT9277B provides programmable soft-start function. When the EN pin is connected to high, a 4μA constant current is sourced to charge an external capacitor. The voltage rate of rise on the COMP pin is limited during the charging period, and so is the peak inductor current. The switching frequency of RT9277A/B can be selected to operate at either 640kHz or 1.2MHz. When the FREQ pin is connected to GND for 640kHz operation, and connected to VIN for 1.2MHz operation. FREQ is preset to 640kHz operation for allowing the FREQ pin unconnected. DS9277A/B-04 April 2011 Current Limitation The switch current is monitored to limit the value not to exceed 1.6A typically. When the switch current reaches 1.6A, the output voltage will be pulled down to limit the total output power to protect the power switch and external components. Shutdown Connect the EN to GND to turn the RT9277A/B off and reduce the supply current to 0.1μA. In this operation, the output voltage is the value of VIN to subtract the forward voltage of catch diode. www.richtek.com 3 RT9277A/B Functional Pin Description Pin No. Pin Name Pin Function RT9277A RT9277B 1 1 COMP 2 2 FB 3 3 EN Shutdown Control Input. Connect EN to GND to turn off the RT9277A/B. 4 4 GND Ground 5 5 LX 6 6 VIN 7 7 FREQ -- 8 SS 8 -- NC www.richtek.com 4 Compensation Pin for Error Amplifier. Connect a compensation network to ground. See the Component Selection Table for the loop compensation. Feedback Pin. Connect an external resistor-divider tap to FB. The typical reference voltage is 1.24V. Switch Pin. Connect the inductor and catch diode to LX pin. Widen and shorten the connected trace to minimize EMI. Supply Pin. Place at least a 1μF ceramic capacitor close to RT9277A/B for bypassing noise. Frequency Select Pin. Oscillator frequency is 640kHz as FREQ connected to GND, and 1.2MHz as FREQ connected to VIN. A 5μA pull-down current is sinking on this pin. Soft-Start Control Pin. 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 VIN high, the soft-start capacitor is charged to VIN. Leave floating for not using soft-start. No Connection DS9277A/B-04 April 2011 RT9277A/B Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Voltage (VIN) ------------------------------------------------------------------------------------------------ −0.3 to 6V LX to GND ------------------------------------------------------------------------------------------------------------- − 0.3V to 16V The other pins -------------------------------------------------------------------------------------------------------- − 0.3V to 6V Power Dissipation, PD @ TA = 70°C MSOP-8 --------------------------------------------------------------------------------------------------------------- 625mW Package Thermal Resistance (Note 2) MSOP-8, θJA ---------------------------------------------------------------------------------------------------------- 160°C/W Junction Temperature ----------------------------------------------------------------------------------------------- 150°C Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260°C Storage Temperature Range --------------------------------------------------------------------------------------- − 65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V Recommended Operating Conditions z z (Note 4) Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3V, FREQ left floating, TA = 25°C, Unless Otherwise specification) Parameter Symbol Test Conditions Min Typ Max Unit System Supply Input Operation Voltage Range V IN 2.5 -- 5.5 V Under Voltage Lock Out UVLO 1.9 2 2.1 V -- 100 -- mV VFB = 1.3V, No switching -- 250 350 uA VFB = 1.0V, Switching, No load -- 2 5 mA Power On Reset Hysteresis Quiescent Current IQ Shut Down Current ISHDN EN = GND -- -- 1 uA Soft start Current (RT9277B) ISS VSS = 1.2V 1.5 4 7 uA FREQ = GND 540 640 740 -- 1200 -- 82 90 96 % 1.222 1.24 1.258 V Switching Regulator Oscillator Free Run Frequency fOSC FREQ = VIN Maximum Duty Cycle kHz Reference Voltage Feedback Reference Voltage V REF VC OMP = 1.24V Error Amplifier Transconductance Gm 70 140 240 uΩ Voltage Gain AV -- 700 -- V/V To be continued DS9277A/B-04 April 2011 www.richtek.com 5 RT9277A/B Parameter Symbol Test Conditions Feedback Voltage Line VCOMP = 1.24V, Regulation 2.5V < VIN < 5.5V Min Typ Max Unit -- 0.05 0.15 %/V -- 200 500 mΩ 1.2 1.6 -- A MOSFET On Resistance of MOSFET RDS(ON) Current Limitation Enable Control Input Input Low Voltage VIL 2.5V ＜ VIN ＜ 5.5V -- -- 0.3 x VIN V Input High Voltage VIH 2.5V ＜ VIN ＜ 5.5V 0.7 x VIN -- -- V -- 0.1 -- V Over Temperature Protection -- 170 -- °C Hysteresis -- 20 -- °C Hysteresis Protection Function Note 1.Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. www.richtek.com 6 DS9277A/B-04 April 2011 RT9277A/B Typical Operating Characteristics Efficiency vs. Output Current Efficiency vs. Output Current 95 100 640kHz 90 640kHz 1.2MHz 85 90 Efficiency (%) Efficiency (%) 1.2MHz 80 75 70 65 60 80 70 60 55 VIN = 3.3V, VOUT = 12V VIN = 5.0V, VOUT = 12V 50 50 0 20 40 60 80 100 120 140 160 180 200 0 50 100 Output Current (mA) 150 200 250 300 350 400 Output Current (mA) Efficiency vs. Output Current Output Voltage vs. Output Current 100 12.06 VIN = 5V 12.04 VIN = 3.5V 80 70 Output Voltage (V) Efficiency (%) 90 60 12.02 640kHz 12.00 1.2MHz 11.98 11.96 VOUT = 9.0V, f = 1.2MHz VIN = 3.3V, VOUT = 12V 50 11.94 0 50 100 150 200 250 300 350 400 0 20 Output Current (mA) 40 60 80 100 120 140 160 180 200 Output Current (mA) Output Voltage vs. Output Current Output Voltage vs. Output Current 9.00 12.06 12.04 12.00 1.2MHz 11.98 640kHz 11.96 11.94 Output Voltage (V) Output Voltage (V) 8.96 12.02 VIN = 3.5V 8.92 VIN = 5V 8.88 8.84 11.92 VOUT = 9.0V, f = 1.2MHz VIN = 5.0V, VOUT = 12V 8.80 11.90 0 50 100 150 200 250 Output Current (mA) DS9277A/B-04 April 2011 300 350 0 50 100 150 200 250 300 350 Output Current (mA) www.richtek.com 7 RT9277A/B Output Voltage vs. Input Voltage 11.986 Output Voltage vs. Input Voltage 11.998 640kHz 11.996 Output Voltage (V) Output Voltage (V) 11.984 1.2MHz 11.982 11.980 11.978 11.976 11.974 11.994 11.992 11.990 11.988 11.986 VOUT = 12V, IOUT = 1mA VOUT = 12V, IOUT = 1mA 11.972 11.984 2.5 2.8 3.0 3.3 3.5 3.8 4.0 4.3 4.5 4.8 5.0 2.5 2.8 3.0 3.3 Input Voltage (V) 3.8 4.0 4.3 4.5 4.8 5.0 Current Limit vs. Input Voltage No Load Supply Current vs. Input Voltage 500 1.8 640kHz 450 640kHz 1.7 Current Limit (mA) No Load Supply Current (uA) 3.5 Input Voltage (V) 400 350 300 250 1.6 1.5 1.4 1.3 200 VOUT = 12V VOUT = 12V 150 1.2 2.5 3 3.5 4 4.5 5 5.5 2.5 3.0 3.5 Input Voltage (V) 4.0 4.5 5.0 5.5 Input Voltage (V) VFB vs. Temperature Frequency vs. Temperature 1300 1.238 1.2MHz 1.2MHz 1.238 1200 Frequency (kHz) V FB Voltage(V) 1.237 1.237 1.236 1.236 1.235 1.235 1.234 1100 1000 900 VIN = 3.3V, VOUT = 12V VIN = 3.3V, VOUT = 12V 1.234 800 -40 -20 0 20 40 Temperature (°C) www.richtek.com 8 60 80 100 -40 -20 0 20 40 60 80 100 Temperature (°C) DS9277A/B-04 April 2011 RT9277A/B Start Up Power Off VL1 (10V/Div) VL1 (10V/Div) VOUT (5V/Div) VOUT (5V/Div) VEN (5V/Div) VEN (5V/Div) ILOAD (1A/Div) VIN = 3.3V, IOUT = 200mA, f = 640kHz ILOAD (1A/Div) VIN = 3.3V, IOUT = 200mA, f = 640kHz Time (2.5ms/Div) Time (500μs/Div) Switching Switching VL1 (10V/Div) VL1 (10V/Div) VOUT ac coupled (100mV/Div) VOUT ac coupled (100mV/Div) IL1 (500mA/Div) IL1 (500mA/Div) VIN = 3.3V, IOUT = 200mA, f = 640kHz VIN = 3.3V, IOUT = 200mA, f = 1.2MHz Time (1μs/Div) Time (1μs/Div) Load Transient Response Load Transient Response VOUT ac coupled (500mV/Div) VOUT ac coupled (500mV/Div) ILOAD (100mA/Div) ILOAD (200mA/Div) VIN = 3.3V, f = 640kHz Time (250μs/Div) DS9277A/B-04 April 2011 VIN = 3.3V, f = 1.2MHz Time (250μs/Div) www.richtek.com 9 RT9277A/B Application Information The design procedure of Boost converter can start from the maximum input current, which is related about inductor, catch-diode input/output capacitor selections and the maximum power which internal switch can stand. It can be derived from maximum output power, minimum input voltage and the efficiency of Boost converter. Once the maximum input current is calculated, the inductor value can be determined and the other components as well. Inductor Selection For a better efficiency in high switching frequency converter, the inductor selection has to use a proper core material such as ferrite core to reduce the core loss and choose low ESR wire to reduce copper loss. The most important point is to prevent the core saturated when handling the maximum peak current. Using a shielded inductor can minimize radiated noise in sensitive applications. The maximum peak inductor current is the maximum input current plus the half of inductor ripple current. The calculated peak current has to be smaller than the current limitation in the electrical characteristics. A typical setting of the inductor ripple current is 20% to 40% of the maximum input current. If the selection is 40%, the maximum peak inductor current is : IPEAK = IIN(MAX) + 1 IRIPPLE = 1.2 × IIN(MAX) 2 ⎡ IOUT(MAX) × VOUT ⎤ = 1.2 × ⎢ ⎥ ⎣ η × VIN(MIN) ⎦ Input Capacitor Selection For better input bypassing, low-ESR ceramic capacitors are recommended for performance. A 10μF input capacitor is sufficient for most applications. For a lower output power requirement application, this value can be decreased. Output Capacitor Selection For lower output voltage ripple, low-ESR ceramic capacitors are recommended. The tantalum capacitors can be used as well, but the ESR is bigger than ceramic capacitor. The output voltage ripple consists of two components: one is the pulsating output ripple current flows through the ESR, and the other is the capacitive ripple caused by charging and discharging. VRIPPLE = VRIPPLE_ESR + VRIPPLE_C ≅ IPEAK × RESR + IPEAK ⎛ VOUT − VIN ⎞ ⎜ ⎟ COUT ⎝ VOUT × fOSC ⎠ Output Voltage The regulated output voltage is calculated by : VOUT = VREF × ⎛⎜1 + R1 ⎞⎟ ⎝ R2 ⎠ Where VREF = 1.24V typical. For most applications, R2 is a suggested a value up to 100kΩ Place the resistor-divider as close to the IC as possible to reduce the noise sensitivity. Loop Compensation The minimum inductance value is derived from the following equation : η × VIN(MIN) × [VOUT -VIN(MIN) ] 2 L= 0.4 × IOUT(MAX) × VOUT × fOSC 2 Depending on the application, the recommended inductor value is between 2.2μH to 10μH. Diode Selection To achieve high efficiency, Schottky diode is good choice for low forward drop voltage and fast switching time. The output diode rating should be able to handle the maximum output voltage, average power dissipation and the pulsating diode peak current. www.richtek.com 10 The RT9277A/B voltage feedback loop can be compensated with an external compensation network consisted of R3, C3 and C4 (As shown in Figure 1). Choose R3 to set the high-frequency integrator gain for fast transient response without over or under compensation. Once R3 is determined, C3 is selected to set the integrator zero to maintain loop stability. The purpose of C4 is to cancel the zero caused by output capacitor and the capacitor ESR. If the ceramic capacitor is selected to be the output capacitor, C4 can be taken off because of the small ESR. C2 is the output capacitor as shown in Figure 1. The following equations give approximate calculations of each component : DS9277A/B-04 April 2011 RT9277A/B R3 = 200 × VOUT 2 × C2 L1 -3 C3 = 0.4 × 10 × L1 VIN 0.005 × RESR × L1 C4 = VOUT 2 The best criterion to optimize the loop compensation is by inspecting the transient response and adjusting the compensation network. Soft-Start Capacitor The soft-start function begins from VSS = 0V to VSS = 1.24V with a 4μA constant current charging to the soft-start capacitor, so the capacitor should be large enough to let the output voltage reach regulation inside the soft-start cycle. Typical value of soft-start capacitor range is from 10nF to 200nF. After the cycle finished, the load can start to draw maximum current as required. Layout Guideline For high frequency switching power supplies, the PCB layout is important step in system application design. In order to let IC achieve good regulation, high efficiency and stability, it is strongly recommended the power components should be placed as close as possible. These traces should be wide and short. The feedback pin and the networks of feedback and compensation should keep away from the power loops, and be shielded with a ground trace or plane to prevent noise coupling. DS9277A/B-04 April 2011 www.richtek.com 11 RT9277A/B Outline Dimension D L E1 E e A2 A A1 b Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.810 1.100 0.032 0.043 A1 0.000 0.150 0.000 0.006 A2 0.750 0.950 0.030 0.037 b 0.220 0.380 0.009 0.015 D 2.900 3.100 0.114 0.122 e 0.650 0.026 E 4.800 5.000 0.189 0.197 E1 2.900 3.100 0.114 0.122 L 0.400 0.800 0.016 0.031 8-Lead MSOP Plastic Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. www.richtek.com 12 DS9277A/B-04 April 2011