RT9277C/D High Performance, Low Noise Boost Converter General Description Features The RT9277C/D is a high performance, low noise, fixed frequency step up DC-DC Converter. The RT9277C/D 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. The RT9277C/D with 640kHz and 1.2MHz operation frequency options provide flexibiltity of minimum output inductor size, maximum efficiency and low BOM cost. z z z z z z z z z z functions such as UVLO, OCP and OTP. z z Package Type F : MSOP-8 QW : WDFN-8L 3x3 (W-Type) z TFT LCD panel OLED Display PCMCIA Cards Portable Device Pin Configurations (TOP VIEW) Lead Plating System G : Green (Halogen Free and Pb Free) Soft Start Function C : External Programmable D : Internal Programmable Note : COMP FB EN GND 8 2 7 3 6 4 5 Richtek products are : ` COMP FB EN GND SS FREQ VIN LX MSOP-8 8 1 3 GND RT9277C/D 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 Internal/External Programmable Soft Start Small MSOP8 Package OCP and OTP Function are Included RoHS Compliant and Halogen Free Applications The RT9277C/D also provides comprehensive protection Ordering Information Efficiency up to 90% 6 4 9 5 2 7 SS FREQ VIN LX WDFN-8L 3x3 RoHS compliant and compatible with the current require- RT9277C ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. COMP FB EN GND 8 2 7 3 6 4 5 NC FREQ VIN LX COMP FB EN GND MSOP-8 8 1 3 GND ` 6 4 9 5 2 7 NC FREQ VIN LX WDFN-8L 3x3 RT9277D DS9277C/D-01 April 2011 www.richtek.com 1 RT9277C/D Typical Application Circuit Chip Enable D1 L1 VOUT + + VIN 2.5V to 5.5V C2 C1 5 LX 6 VIN GND 4 EN 3 7 FREQ FB 8 SS COMP 2 1 R1 R3 C4 C5 RT9277C 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 8 NC COMP 2 1 R1 R3 C4 RT9277D R2 C3 Figure 2 Table 1. Recommended Components Symbol VIN V OUT FOSC (unit) (V) (V) (Hz) C1 (μF) L1 (μH) C2 (μF) R3 (kΩ) C3 (pF) C4 (pF) Application 1 3.3 9 1.2M 10 4.7(TDK SLF6028) 33 (ceramic) 82 820 10 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 + 4µA VIN Protection SoftStart Summing Comparator + Control and Driver Logic Clock SS LX N GND 5µA FREQ Oscillator Slope Compensation Current Sense RT9277C www.richtek.com 2 DS9277C/D-01 April 2011 RT9277C/D LX VIN VFB EN COMP FB 1.24V Internal Soft-Start Protection Error Amplifier + Summing Comparator + Control and Driver Logic VIN LX N Clock GND 5µA FREQ Oscillator Slope Compensation Current Sense RT9277D Operation The RT9277C/D 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. Current Limitation Soft-Start The switching frequency of RT9277C/D 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. The RT9277C 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 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 RT9277C/D 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. Frequency Selection When the EN pin is connected to GND, the external capacitor will be discharged to ground for the next time soft-start. DS9277C/D-01 April 2011 www.richtek.com 3 RT9277C/D Functional Pin Description Pin No. Pin Name Pin Function RT9277C RT9277D 1 1 COMP 2 2 FB 3 3 EN Shutdown Control Input. Connect EN to GND to turn off the RT9277C/D. 4, 9 (Exposed pad) 4, 9 (Exposed pad) GND Ground Pin. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 5 5 LX Switch Pin. Connect the inductor and catch diode to LX pin. Widen and shorten the connected trace to minimize EMI. 6 6 VIN Supply Pin. Place at least a 1μF ceramic capacitor close to RT9277C/D for bypassing noise. 7 7 FREQ Frequency Select Pin. Oscillator frequency is 640kHz as FREQ is connected to GN D, and 1.2MHz as FREQ is connected to VIN. A 5μA pull-down current is sinking on this pin. 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. 8 -- SS Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. A 4μA constant current charges the soft-start capacitor. When EN is connected to GND , the soft-start capacitor is discharged. W hen EN is connected to VIN high, the soft-start capacitor is charged to VIN. Leave floating for not using soft-start. -- 8 NC No Internal C onnection. www.richtek.com 4 DS9277C/D-01 April 2011 RT9277C/D 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 WDFN-8L 3x3 --------------------------------------------------------------------------------------------------------- 926mW Package Thermal Resistance (Note 2) MSOP-8, θJA ---------------------------------------------------------------------------------------------------------- 160°C/W WDFN-8L 3x3, θJA --------------------------------------------------------------------------------------------------- 108°C/W WDFN-8L 3x3, θJC --------------------------------------------------------------------------------------------------- 7.5W 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 VIN 2.5 -- 5.5 V Under Voltage Lock Out UVLO 1.9 2 2.1 V -- 100 -- mV VFB = 1.3V, No switching -- 250 500 μA VFB = 1.0V, Switching, No load -- 2 5 mA Power On Reset Hysteresis Quiescent Current IQ Shut Down Current ISH DN EN = GND -- -- 1 μA Soft start Current (RT9277C) ISS VSS = 1.2V 1.5 4 7 μA FREQ = GND 540 640 740 -- 1200 -- 82 90 96 % 1.227 1.24 1.253 V Switching Regulator Oscillator Free Run Frequency fOSC FREQ = VIN Maximum Duty Cycle kHz Reference Voltage Feedback Reference Voltage VREF VCOMP = 1.24V To be continued DS9277C/D-01 April 2011 www.richtek.com 5 RT9277C/D Parameter Symbol Test Conditions Min Typ Max Unit Error Amplifier Transconductance Gm 70 140 240 μΩ Voltage Gain AV -- 700 -- V/V -- 0.05 0.15 %/V -- 200 500 mΩ 1.2 1.6 -- A Feedback Voltage Line Regulation VCOMP = 1.24V, 2.5V < VIN < 5.5V MOSFET On Resistance of MOSFET R DS(ON) Current Limitation Enable Control Input Input Low Voltage V IL 2.5V ＜ VIN ＜ 5.5V -- -- 0.3 x VIN V Input High Voltage V IH 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 DS9277C/D-01 April 2011 RT9277C/D Typical Operating Characteristics Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 90 VIN = 5V 80 VIN = 3.3V VIN = 5V 70 Efficiency(%) Efficiency (%) 80 60 50 40 30 70 60 50 40 30 20 20 10 10 fOSC = 1.2MHz, L = 4.7μH, VOUT = 11.6V 0 50 100 150 200 250 fOSC = 640kHz, L = 10μH, VOUT = 11.6V 0 0 0 300 50 11.70 11.68 11.68 Output Voltage (V) Output Voltage (V) 11.66 VIN = 3.3V 11.62 11.60 150 200 250 300 Output Voltage vs. Output Current Output Voltage vs. Output Current 11.70 11.64 100 Output Current(mA) Output Current (mA) VIN = 5V 11.58 11.56 11.54 11.66 VIN = 3.3V 11.64 11.62 VIN = 5V 11.60 11.58 11.56 11.54 11.52 11.52 fOSC = 1.2MHz, L = 4.7μH 11.50 0 50 100 150 200 250 fOSC = 640kHz, L = 10μH 11.50 300 0 50 Output Current (mA) 100 150 200 250 300 Output Current (mA) Output Voltage vs. Input Voltage Output Voltage vs. Input Voltage 11.70 11.70 11.65 11.65 IOUT = 100mA Output Voltage(V) Output Voltage (V) VIN = 3.3V IOUT = 200mA 11.60 11.55 IOUT = 0mA 11.50 IOUT = 100mA IOUT = 200mA 11.60 IOUT = 0mA 11.55 11.50 11.45 11.45 fOSC = 1.2MHz, L = 4.7μH 2.5 3.1 3.7 4.3 Input Voltage (V) DS9277C/D-01 April 2011 4.9 fOSC = 640kHz, L = 10μH 11.40 11.40 5.5 2.5 3.1 3.7 4.3 4.9 5.5 Input Voltage(V) www.richtek.com 7 RT9277C/D Feedback Voltage vs. Input Voltage Feedback Voltage vs. Temperature 1.240 1.234 Feedback Voltage (V) Feedback Voltage (V) 1.236 1.232 1.230 1.228 1.235 1.230 1.225 1.220 1.215 fOSC = 640kHz 1.226 2.5 3 3.5 4 4.5 5 fOSC = 640kHz 1.210 5.5 -40 -20 0 Input Voltage (V) 20 40 60 80 100 120 140 Temperature (°C) Quiescent Current vs. Input Voltage Quiescent Current vs. Input Voltage 0.4 5 Quiescent Current (mA) Quiescent Current (mA) 4.5 4 3.5 3 2.5 2 0.35 0.3 0.25 1.5 VFB = 1.3V VFB = 1V 1 2.5 3 3.5 4 4.5 5 0.2 2.5 5.5 3 Input Voltage (V) 3.5 4 4.5 5 5.5 Input Voltage (V) Current Limit vs. Input Voltage Shutdown Current vs. Input Voltage 0.20 2 Inductor Current (A) Shutdown Current (uA)1 1.8 0.15 0.10 0.05 1.6 1.4 1.2 1 0.8 0.6 0.4 EN = 0V 0.00 0.2 fOSC = 1.2MHz, VOUT = 11.6V 0 2.5 3 3.5 4 4.5 Input Voltage (V) www.richtek.com 8 5 5.5 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) DS9277C/D-01 April 2011 RT9277C/D Frequency vs. Temperature Load Transient Response 1300 Frequency(KHz) 1200 VOUT ac coupled (500mV/Div) 1100 1000 ILOAD (200mA/Div) 900 VIN = 3.3V, VOUT = 11.6V 800 -40 -20 0 20 40 60 80 VIN = 3.3V, f = 640kHz 100 Time (250μs/Div) Temperature (°C) 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) 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 Time (1μs/Div) DS9277C/D-01 April 2011 VIN = 3.3V, IOUT = 200mA, f = 640kHz VIN = 3.3V, IOUT = 200mA, f = 1.2MHz Time (1μs/Div) www.richtek.com 9 RT9277C/D Application Information The IC 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. 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) ⎦ Where IPK is the maximum peak current of inductor, IRIPPLE is the ripple current of inductor and η is the efficiency of boost converter. The minimum inductance value is derived from the following equation : η × VIN(MIN) × [VOUT -VIN(MIN) ] 2 L= 2 0.4 × IOUT(MAX) × VOUT × fOSC Where fOSC is the switching frequency of boost converter. Depending on the application, the recommended inductor value is between 2.2μH to 10μH. Diode Selection To achieve high efficiency, Schottky diode is a 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 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 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 × ESRCOUT + IPEAK COUT ⎛ VOUT − VIN ⎞ ⎜ ⎟ ⎝ VOUT × fOSC ⎠ Where IPEAK is the ripple current of COUT and ESRCOUT is equivalent series resistance of COUT. Output Voltage The regulated output voltage is calculated by : VOUT = VREF × ⎛⎜1 + R1 ⎞⎟ ⎝ R2 ⎠ Where VREF is the feedback referecne voltage and typical value is 1.24V. 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 RT9277C/D 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 : DS9277C/D-01 April 2011 RT9277C/D R3 = Layout Consideration 200 × VOUT 2 × C2 L1 For best performance of the RT9277C/D, the following guidelines must be strictly followed. -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. ` Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. ` The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. ` Keep the main current traces as possible as short and wide. ` LX node of DC/DC converter is with high frequency voltage swing. It should be kept at a small area. ` Place the feedback and compensation components as close as possible to the IC and keep away from the noisy devices. Soft-Start Capacitor The soft-start function begins from VSS = 0V to 1.24V with a 4μA constant current charging to the soft-start capacitor, so the capacitor should be large enough for the output voltage to reach regulation inside the soft-start cycle. Typical value of soft-start capacitor range is from 10nF to 200nF. Place feedback (R1, R2) and compensation ( R 3 , C 3 , C 4 ) components as close as possible to the IC and keep away from the noisy devices. GND C3 R2 R1 AVDD R3 COMP FB EN GND C4 1 2 3 4 8 7 6 5 C5 LX node of DC/DC converter is with high frequency voltage swing. It should be kept at a SS small area. FREQ VIN VIN L1 LX C2 D1 AVDD GND The GND should be connected to a strong ground plane for heat sinking and noise protection. C1 Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. Figure 3. PCB Layout Guide DS9277C/D-01 April 2011 www.richtek.com 11 RT9277C/D 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 www.richtek.com 12 DS9277C/D-01 April 2011 RT9277C/D 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 0.200 0.300 0.008 0.012 D 2.950 3.050 0.116 0.120 D2 2.100 2.350 0.083 0.093 E 2.950 3.050 0.116 0.120 E2 1.350 1.600 0.053 0.063 e L 0.650 0.425 0.026 0.525 0.017 0.021 W-Type 8L DFN 3x3 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. DS9277C/D-01 April 2011 www.richtek.com 13