RT8030 1A, 2.2MHz, Synchronous Step-Down Regulator General Description Features The RT8030 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.6V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering output current up to 1A. z z z z z The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. Switching frequency is set by an external resistor or can be synchronized to an external clock. 100% duty cycle provides low dropout operation extending battery life in portable systems. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. z z z High Efficiency : Up to 95% Low RDS(ON) Internal Switches : 160mΩ Ω Programmable Frequency : 300kHz to 2.5MHz No Schottky Diode Required 0.8V Reference Allows Low Output Voltage Forced Continuous Mode Operation Low Dropout Operation : 100% Duty Cycle RoHS Compliant and Halogen Free Applications z z z z RT8030 operation in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference. 100% duty cycle in Low Dropout Operation further maximize battery life. z z Portable Instruments Battery-Powered Equipment Notebook Computers Distributed Power Systems IP Phones Digital Cameras Ordering Information RT8030 Pin Configurations Package Type S : SOP-8 (TOP VIEW) SHDN/RT Lead Plating System G : Green (Halogen Free and Pb Free) 8 COMP GND 2 7 FB Note : LX 3 6 VDD Richtek products are : PGND 4 5 PVDD ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. SOP-8 ` Suitable for use in SnPb or Pb-free soldering processes. Typical Application Circuit RT8030 VIN 2.6V to 5.5V CIN 10µF x 2 5 PVDD LX 6 VDD FB 7 4 ROSC 137k 3 PGND 1 SHDN/RT COMP 8 GND 2 L1 2.2µH VOUT 1.5V/1A R1 210k COUT 10µF x 2 RCOMP 13k CCOMP 1nF R2 240k Note : Using all Ceramic Capacitors DS8030-02 March 2011 www.richtek.com 1 RT8030 Functional Pin Description Pin No. Pin Name Pin Function 1 SHDN/RT 2 GND 3 LX Internal Power MOSFET Switches Output. Connect this pin to the inductor. 4 PGND Power Ground. Connect this pin close to the (−) terminal of C IN and COUT . 5 PVDD Power Input Supply. Decouple this pin to PGND with a capacitor. 6 VDD 7 FB Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. Forcing this pin to V DD causes the device to be shut down. Signal Ground. All small-signal components and compensation components should connect to this ground, which in turn connects to PGND at one point. Signal Input Supply. Decouple this pin to GND with a capacitor. Normally VDD is equal to PVDD. Feedback Pin. Receives the feedback voltage from a resistive divider connected across the output. Error Amplifier Compensation Point. The current comparator threshold increases with 8 COMP this control voltage. Connect external compensation elements to this pin to stabilize the control loop. Function Block Diagram SHDN/RT PVDD ISEN SD OSC Slope Com COMP 0.8V EA FB OC Limit Output Clamp Driver Int-SS LX 0.9V Control Logic 0.7V NISEN VDD POR 0.4V VREF www.richtek.com 2 PGND NMOS I Limit OTP GND DS8030-02 March 2011 RT8030 Operation Main Control Loop Slope Compensation and Inductor Peak Current The RT8030 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error amplifier adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load current. When the top power MOSFET shuts off, the synchronous power switch (N-MOSFET) turns on until either the bottom current limit is reached or the beginning of the next clock cycle. Slope compensation provides stability in constant frequency architectures by preventing sub-harmonic oscillations at duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8030, however, separated inductor current signals are used to monitor over current condition. This keeps the maximum output current relatively constant regardless of duty cycle. The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching frequency can range from 300kHz to 2.5MHz. Short Circuit Protection When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring. Dropout Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually reaching 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-MOSFET and the inductor. Low Supply Operation The RT8030 is designed to operate down to an input supply voltage of 2.6V. One important consideration at low input supply voltages is that the RDS(ON) of the P-Channel and N-Channel power switches increases. The user should calculate the power dissipation when the RT8030 is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded. DS8030-02 March 2011 www.richtek.com 3 RT8030 Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VDD, PVDD ------------------------------------------------------------------------------- −0.3V to 6V LX Pin Switch Voltage -------------------------------------------------------------------------------------------- −0.3V to (PVDD + 0.3V) Other I/O Pin Voltages ------------------------------------------------------------------------------------------- −0.3V to (VDD + 0.3V) LX Pin Switch Current -------------------------------------------------------------------------------------------- 4A Power Dissipation, PD @ TA = 25°C SOP-8 --------------------------------------------------------------------------------------------------------------- 0.909W Package Thermal Resistance (Note 2) SOP-8, θJA ---------------------------------------------------------------------------------------------------------- 110°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 z (Note 4) Input Voltage Range, 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 Min Typ Max Unit 0.784 0.8 0.816 V Active, VFB = 0.78V, Not Switching -- 460 -- μA Shutdown -- -- 1 μA VIN = 2.7V to 5.5V -- 0.04 -- %/V 0A < ILOAD < 1A -- 0.25 -- % gm -- 800 -- μS Current Sense Transresistance RT -- 0.4 -- Ω ROSC = 332k 0.8 1 1.2 MHz Switching Frequency 0.3 -- 2.5 MHz Feedback Reference Voltage Symbol VREF DC Bias Current Output Voltage Line Regulation Output Voltage Load Regulation Error Amplifier Transconductance Test Conditions Switching Frequency Switch On Resistance, High RPMOS I SW = 0.5A -- 150 -- mΩ Switch On Resistance, Low RNMOS I SW = 0.5A -- 160 -- mΩ Peak Current Limit ILIM 2.2 3.2 -- A VDD Rising -- 2.4 -- V VDD Falling -- 2.3 -- V Under Voltage Lockout Threshold Shutdown Threshold www.richtek.com 4 VSHDN/RT -- VIN – 0.7 VIN – 0.4 V DS8030-02 March 2011 RT8030 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 4-layers high effective thermal conductivity test board of JEDEC 51-7 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. DS8030-02 March 2011 www.richtek.com 5 RT8030 Typical Operating Characteristics Efficiency vs. Output Current 100 Output Voltage vs. Output Current 1.515 VIN = 3.3V 90 1.510 VIN = 5V Output Voltage (V) Efficiency (%) 80 70 60 50 40 30 20 1.505 1.500 1.495 1.490 10 VOUT = 1.5V, L = 2.2uH VIN = 5V, VOUT = 1.5V 1.485 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 1 0.1 0.2 0.3 Output Voltage vs. Input Voltage 0.6 0.7 0.8 0.9 1 Output Voltage vs. Temperature 1.515 1.510 1.510 Output Voltage (V) 1.515 1.505 1.500 1.495 1.490 1.505 1.500 1.495 1.490 VIN = 5V, VOUT = 1.5V VOUT = 1.5V 1.485 1.485 2.5 3 3.5 4 4.5 5 5.5 -50 -25 0 Input Voltage (V) 25 50 75 100 125 Temperature (°C) Switching Frequency vs. Input Voltage Switching Frequency vs. Temperature 2.40 2.40 2.35 2.35 Switching Frequency (MHz) Switching Frequency (MHz) 0.5 Output Current (A) Output Current (A) Output Voltage (V) 0.4 2.30 2.25 2.20 2.15 2.10 2.05 2.30 2.25 2.20 2.15 2.10 2.05 VIN = 5V, VOUT = 1.5V, IOUT = 300mA, ROSC = 137kΩ VOUT = 1.5V, IOUT = 300mA, ROSC = 137kΩ 2.00 2.00 2.5 3 3.5 4 4.5 Input Voltage (V) www.richtek.com 6 5 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) DS8030-02 March 2011 RT8030 Load Transient Response Quiescent Current vs. Input Voltage 550 Quiescent Current (uA) VOUT (50mV/Div) IOUT (1A/Div) 530 510 490 470 VIN = 5V, VOUT = 1.5V, IOUT = 0A to 1A 450 Time (50us/Div) 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 Input Voltage (V) Quiescent Current vs. Temperature Output Current Limit vs. Input Voltage 500 4.0 Output Current Limit (A) Quiescent Current (uA) 3.8 480 460 440 420 3.5 3.3 3.0 2.8 2.5 2.3 VIN = 3.3V 400 -50 -25 0 25 50 75 100 VOUT = 1.5V 2.0 2.5 125 Temperature (°C) 3 3.5 4 4.5 5 5.5 Input Voltage (V) Output Current Limit vs. Temperature Output Ripple 4.0 Output Current Limit (A) 3.8 VOUT (5mV/Div) 3.5 3.3 3.0 2.8 VLX (5V/Div) 2.5 2.3 VIN = 5V, VOUT = 1.5V VIN = 5V, VOUT = 1.5V, IOUT = 0A 2.0 -50 -25 0 25 50 75 100 125 Time (250ns/Div) Temperature (°C) DS8030-02 March 2011 www.richtek.com 7 RT8030 Power On Power Off VIN = 5V, VOUT = 1.5V, IOUT = 1A VIN (5V/Div) VIN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) IOUT (0.5A/Div) IOUT (0.5A/Div) VIN = 5V, VOUT = 1.5V, IOUT = 1A Time (1ms/Div) www.richtek.com 8 Time (5ms/Div) DS8030-02 March 2011 RT8030 Application Information Operating Frequency Selection of the operating frequency is a tradeoff between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values. Operation at lower frequency improves efficiency by reducing internal gate charge and switching losses but requires larger inductance and/or capacitance to maintain low output ripple voltage. The operating frequency of the RT8030 is determined by an external resistor that is connected between the RT pin and ground. The value of the resistor sets the ramp current that is used to charge and discharge an internal timing capacitor within the oscillator. The ROSC resistor value can be determined by examining the frequency vs. ROSC curve. Although frequencies as high as 2.5MHz are possible, the minimum on-time of the RT8030 imposes a minimum limit on the operating duty cycle. The minimum on-time is typically 110ns. Therefore, the minimum duty cycle is equal to 100 x 110ns x f(Hz). Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. ⎡V ⎤⎡ V ⎤ ΔIL = ⎢ OUT ⎥ ⎢1 − OUT ⎥ VIN ⎦ ⎣ f × L ⎦⎣ Having a lower ripple current reduces the ESR losses in the output capacitors and the output voltage ripple. Highest efficiency operation is achieved at low frequency with small ripple current. This, however, requires a large inductor. A reasonable starting point for selecting the ripple current is ΔI = 0.4(IMAX). The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : DS8030-02 March 2011 ⎡ VOUT ⎤ ⎡ VOUT ⎤ L=⎢ ⎥ ⎥ ⎢1 − V f I × Δ L(MAX) IN(MAX) ⎦ ⎦⎣ ⎣ The transition from low current operation begins when the peak inductor current falls below the minimum peak current. Lower inductor values result in higher ripple current which causes this to occur at lower load currents. This causes a dip in efficiency in the upper range of low current operation. 2.5 ROSC = 154k for 2MHz 2.0 Frequency (MHz) The basic RT8030 application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. 1.5 ROSC = 332k for 1MHz 1.0 0.5 0.0 0 100 200 300 400 500 600 700 800 900 1000 100 0 ROSC Resistance RRT (k⎝ ) (kΩ) Figure 1. Switching Frequency vs. ROSC Resistance Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. This result in an abrupt increase in inductor ripple current and consequent output voltage ripple. www.richtek.com 9 RT8030 Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style inductor to use mainly depends on the price vs. size requirements and any radiated field/EMI requirements. CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : IRMS = IOUT(MAX) VOUT VIN VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = I OUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔVOUT, is determined by : ⎡ 1 ⎤ ΔVOUT ≤ ΔIL ⎢ESR + 8fCOUT ⎥⎦ ⎣ The output ripple is highest at maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are www.richtek.com 10 all available in surface mount packages. Special polymer capacitors offer very low ESR but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Output Voltage Programming The output voltage is set by an external resistive divider according to the following equation : VOUT = VREF × ⎛⎜1 + R1 ⎞⎟ ⎝ R2 ⎠ where VREF equals to 0.8V typical. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 2. V OUT R1 FB RT8030 R2 GND Figure 2. Setting the Output Voltage DS8030-02 March 2011 RT8030 Outline Dimension H A M J B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.050 0.254 0.002 0.010 J 5.791 6.200 0.228 0.244 M 0.400 1.270 0.016 0.050 8-Lead SOP 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. DS8030-02 March 2011 www.richtek.com 11