APPLICATION NOTE Low power consumption and high efficiency LV5980MC Step-down switching regulator 1. Introduction The LV5980MC is a fixed 370 KHz, high-output-current, Non-synchronous PWM converter that integrates a low-resistance, high-side MOSFET and a Customer Chosen, External Diode for the rectification. The LV5980MC utilizes externally compensated current mode control to provide good transient response, ease of implementation, and excellent loop stability. It regulates input voltages from 4.5 V to 23 V down to an output voltage as low as 1.235 V and is able to supply up to 3.0 A of load current. The LV5980MC includes Power Save Feature to enhance efficiency during Light Load. In low consumption mode, the device show operating current of 63 uA from VIN by shutting down unnecessary circuits. Key Features Power Save feature Enhanced Light Load efficiency Low consumption mode (ISLEEP 63uA) High efficiency (100mΩ high-side MOSFET) 4.5 V to 23 V Operating input voltage range Fixed 370 kHz PWM operation Pulse-by-Pulse current limiting Short circuit protection Programmable soft start Thermal shutdown 2. Evaluation board performance summary Parameter Input Supply Voltage Output Voltage Current Limit Peak Oscillatory Frequency Rating Min 8 3.5 Typ 15 5 4.7 370 Max 20 6.2 Unit V V A kHz Figure 1: LV5980MC Evaluation Board 1 / 13 LV5980MC Block Diagram Figure 2: LV5980MC Block Diagram Schematic Figure 3: LV5980MC 5V Schematic 2 / 13 LV5980MC Bill of Materials Designator Manufacturer Part Number Value Tolerance Qty Manufacturer U1 LV5980MC - - 1 SANYO Semiconductor L1 R1 R2 R3 C1 C2 C3 C5 C6 C7 D1 FDVE1040-100M RK73B1JTTD473J RK73H1JTTD2203F RK73H1JTTD6803F GRM31CB31E106K C2012JB0J106M GRM188B31E105K GRM188B31E105K GRM188B11H472K GRM188B11H222K SB3003CH 10uH / 5.2A 47kohms 220kohms 680kohms 10uF / 25V 10uF / 6.3V 1uF / 25V 1uF / 25V 4.7nF / 50V 2.2nF / 50V - 10% 5% 1% 1% 10% 10% 10% 10% 10% 10% - 1 1 1 1 2 3 1 1 1 1 1 TOKO INC KOA KOA KOA Murata TDK Corp Murata Murata Murata Murata SANYO Semiconductor IN/OUT conditions Symbol VIN VOUT GND Functions Power supply input pin. DC/DC converter output pin. Ground pin. 3. Connection Diagram and Test Set UP description Oscilloscope DC Power Supply Load Figure 4: LV5980MC Test Set UP Diagram Test Set UP description 1. Connect the Load between VOUT and GND. 2. Connect the DC power supply with VIN and GND. 3. The output becomes a set voltage. 3 / 13 LV5980MC 4. Results Application curves for LV5980MCGEVB at Ta = 25°C Efficiency / VOUT = 3.3V 100 Loss / VOUT = 3.3V 2.5 VIN = 5V 90 Loss [W] VIN = 15V 70 VIN = 12V 60 50 1.5 1 40 30 0.5 20 L=10uH R1=33kΩ 10 0.1 1 10 100 1000 L=10uH R1=33kΩ 0 0 10000 1000 Efficiency / VOUT = 5V 100 VIN = 8V VIN = 8V VIN = 15V 90 VIN = 12V 2 VIN = 15V VIN = 12V 70 Loss [W] Efficiency [%] 3000 Loss / VOUT = 5V 2.5 80 2000 Load Current [mA] Load Current [mA] 60 50 1.5 1 40 30 0.5 20 L=10uH R1=47kΩ 10 0.1 1 10 100 1000 L=10uH R1=47kΩ 0 10000 0 1000 Load Current [mA] Line Regulation / VOUT=5V VIN = 12V 0.1 0 -0.1 0 1000 2000 Load Current [mA] 3000 0.005 Output Voltage Regulation [%] VIN = 8V VIN = 15V 2000 Load Current [mA] Load Regulation / VOUT=5V 0.2 Output Voltage Regulation [%] VIN = 8V VIN = 15V 2 80 Efficiency [%] VIN = 5V VIN = 12V VIN = 8V 3000 0.004 0.003 0.002 0.001 0.000 -0.001 -0.002 -0.003 -0.004 -0.005 8 10 12 14 16 18 20 Input Voltage [V] 4 / 13 LV5980MC Output ripple voltage Io=20mA Output ripple voltage Io=2A SW 10V/div SW 10V/div Vo 20mV/div Vo 20mV/di IL 1A/div IL 1A/div 2us/div 2us/div Load transient response IOUT = 0.5 ⇔2.5A Vo 0.2V/div Short circuit protection Vo 5V/div SS 5V/div SW 20V/div Io 2A/div 0.5ms/div IL 5A/div 20ms/div Start UP Sequence No Load Start UP Sequence Io=2A VIN 10V/div VIN 10V/div SS 2V/div SS 2V/div Vo 2V/div Vo 2V/div IL 1A/div IL 1A/div 1ms/div 1ms/div 5 / 13 LV5980MC 5. Detailed Description Output Voltage Setting Output voltage (VOUT) is configurable by the resistance R3 between VOUT and FB and the R2 between FB and GND. VOUT is given by the following equation (1). VOUT ( 1 R3 R3 ) VREF ( 1 ) 1.235 [V] R2 R2 (1) Soft Start Soft start time (TSS) is configurable by the capacitor (C5) between SS/HICCUP and GND. The setting value of TSS is given by the equation (2). TSS C5 VREF 1.235 C5 [ms ] ISS 1.8 10 6 (2) Hiccup Over-Current Protection Over-current limit (ICL) is set to 4.7A in the IC. When the peak value of inductor current is higher than 4.7A for 15 consecutive times, the protection deems it as over current and stops the IC. Stop period (THIC) is defined by the discharging time of the SS/HICCUP. When SS/HICCUP is lower than 0.15V, the IC starts up. When SS/HICCUP is higher than 0.3V and then over current is detected, the IC stops again. And when SS/HICCUP is higher than 1.235V, the discharge starts again. When the protection does not detect over-current status, the IC starts up again. Figure 5: Hiccup over-current protection time chart Power-save Feature The LV5980MC has Power-saving feature (Low consumption Mode) to enhance efficiency during light load. By shutting down unnecessary circuits, operating current of the IC is minimized and high efficiency is realized. When the output load current decrease, the COMP pin voltage falls to 0.9V and the device enters Low consumption Mode (The COMP pin is connected internally to an Init. comparator which compares with 0.9V reference). In low consumption mode, the device show operating current of 63 uA from VIN. When the COMP pin voltage is larger than 0.9V, IC operates in continuous Mode (PWM Mode). 6 / 13 LV5980MC 6. Design Procedure Inductor Selection When conditions for input voltage, output voltage and ripple current are defined, the following equations (4) give inductance value. L VIN VOUT TON ⊿IR 1 TON FOSC VF VIN VOUT ・ (4) VIN VOUT VOUT VF 1 FOSC : Oscillatory Frequency : Forward voltage of Schottky Barrier diode : Input voltage : Output voltage Inductor current: Peak value (IRP) Current peak value (IPR) of the inductor is given by the equation (5). IRP IOUT VIN VOUT TON 2L (5) Make sure that rating current value of the inductor is higher than a peak value of ripple current. ・ Inductor current: ripple current (∆IR) Ripple current (∆IR) is given by the equation (6). ⊿ IR VIN VOUT TON L (6) When load current (IOUT) is less than 1/2 of the ripple current, inductor current flows discontinuously. Output Capacitor Selection Make sure to use a capacitor with low impedance for switching power supply because of large ripple current flows through output capacitor. This IC is a switching regulator which adopts current mode control method. Therefore, you can use capacitor such as ceramic capacitor and OS capacitor in which equivalent series resistance (ESR) is exceedingly small. Effective value is given by the equation (7) because the ripple current (AC) that flows through output capacitor is saw tooth wave. IC _ OUT 1 2 3 VOUT VIN VOUT ［Arms］ L FOSC VIN (7) Input Capacitor Selection Ripple current flows through input capacitor which is higher than that of the output capacitors. Therefore, caution is also required for allowable ripple current value. The effective value of the ripple current flows through input capacitor is given by the equation (8). 1 D IOUT ［Arms］ IC _ IN D D (8) TON VOUT T VIN In (8), D signifies the ratio between ON/OFF period. When the value is 0.5, the ripple current is at a maximum. Make sure that the input capacitor does not exceed the allowable ripple current value given by (8). With (8), if VIN=15V, VOUT=5V, IOUT=1.0A and FOSC=370 kHz, then IC_IN value is about 0.471Arms. In the board wiring from input capacitor, VIN to GND, make sure that wiring is wide enough to keep impedance low because of the current fluctuation. Make sure to connect input capacitor near output capacitor to lower voltage bound due to regeneration current.When change of load current is excessive (IOUT: high low), the power of output electric capacitor is regenerated to input capacitor. If input capacitor is small, input voltage increases. Therefore, you need to implement a large input capacitor. Regeneration power changes according to the change of output voltage, inductance of a coil and load current. 7 / 13 LV5980MC Selection of external phase compensation component This IC adopts current mode control which allows use of ceramic capacitor with low ESR and solid polymer capacitor such as OS capacitor for output capacitor with simple phase compensation. Therefore, you can design long-life and high quality step-down power supply circuit easily. Frequency Characteristics The frequency characteristic of this IC is constituted with the following transfer functions. (1) Output resistance breeder (2) Voltage gain of error amplifier Current gain (3) Impedance of phase compensation external element (4) Current sense loop gain (5) Output smoothing impedance : HR : GVEA : GMEA : ZC : GCS : ZO Figure 6: Compensation Network Closed loop gain is obtained with the following formula (9). G H R G MER Z C G CS Z O VREF G MER VOUT RL 1 G CS R C sC C 1 sC O R L (9) Frequency characteristics of the closed loop gain is given by pole fp1 consists of output capacitor CO and output load resistance RL, zero point fz consists of external capacitor CC of the phase compensation and resistance RC, and pole fp2 consists of output impedance ZER of error amplifier and external capacitor of phase compensation CC as shown in formula (9). fp1, fz, fp2 are obtained with the following equations (10) to (12). 1 2 C O R L 1 fz 2 C C R C 1 fp2 2 ZER CC fp1 (10) (11) (12) 8 / 13 LV5980MC Calculation of external phase compensation constant Generally, to stabilize switching regulator, the frequency where closed loop gain is 1 (zero-cross frequency fZC) 1 1 should be of the switching frequency (or ). Since the switching frequency of this IC is 370 kHz, the 10 5 zero-cross frequency should be 37 kHz. Based on the above condition, we obtain the following formula (13). VREF RL 1 G CS GMER R C 1 VOUT sCC 1 sC O R L (13) As for zero-cross frequency, since the impedance element of phase compensation is RC 1 , the following sCC equation (14) is obtained. VREF RL GMER R C G CS 1 VOUT 1 2 f ZC C O R L (14) Phase compensation external resistance can be obtained with the following formula (15), the variation of the formula (14). Since 2 fZC CO RL 1 in the equation (15), we know that the external resistance is independent of load resistance. RC VOUT 1 1 1 2 f ZC C O R L VREF GMER G CS RL (15) When output is 5V and load resistance is 5Ω (1A load), the resistances of phase compensation are as follows. GCS = 2.7A/V, GMER = 220uA/V, fZC = 37kHz 5 1 1 1 2 3.14 37 10 3 30 10 6 5 48.898... 10 3 6 1.235 220 10 2 .7 5 48.90 [k] RC If frequency of zero point fz and pole fp1 are in the same position, they cancel out each other. Therefore, only the pole frequency remains for frequency characteristics of the closed loop gain. In other words, gain decreases at -20dB/dec and phase only rotates by 90º and this allows characteristics where oscillation never occurs. fp1 fz 1 1 2 C O R L 2 C C R C CC R L C O 5 30 10 6 3.067... 10 9 3 RC 48.9 10 3 .07 [nF ] The above shows external compensation constant obtained through ideal equations. In reality, we need to define phase constant through testing to verify constant IC operation at all temperature range, load range and input voltage range. In the evaluation board for delivery, phase compensation constants are defined based on the above constants. The zero-cross frequency required in the actual system board, in other word, transient response is adjusted by external compensation resistance. Also, if the influence of noise is significant, use of external phase compensation capacitor with higher value is recommended. 9 / 13 LV5980MC The table of compensation values is provided below. VIN VOUT L R2 (V) (V) (uH) (kohm) 1.235 4.7 220 1.8 5.6 220 8 3.3 6.8 180 5 8.2 220 1.235 4.7 220 1.8 5.6 220 12 3.3 8.2 180 5 10 220 8 15 150 1.235 5.6 220 1.8 6.8 220 3.3 10 180 18 5 12 220 8 15 150 15 33 82 *: 10uF / 25V (Murata : GRM31CB31E106K) R3 (kohm) RC (kohm) CC (nF) CO (uF) 0 100 300 680 0 100 300 680 820 0 100 300 680 820 910 20 24 33 39 20 24 33 39 47 20 24 33 39 47 51 3.3 3.3 4.7 4.7 3.3 3.3 4.7 4.7 5.6 3.3 3.3 4.7 4.7 5.6 5.6 30 30 30 30 30 30 30 30 30* 30 30 30 30 30* 30* The zero-cross frequency required in the actual system board, in other word, transient response is adjusted by RC. Also, if the influence of noise is significant, use of CC with higher value is recommended. 10 / 13 LV5980MC 7. Suggested Circuit Layout Figure 7: 4-layer PCB with all components on top side Top-Side layout Bottom-Side layout 2nd/3rd layout 11 / 13 LV5980MC Pattern design of the board affects the characteristics of DC-DC converter. This IC switches high current at a high speed. Therefore, if inductance element in a pattern wiring is high, it could be the cause of noise. Make sure that the pattern of the main circuit is fat and short. Figure 8: LV5980MCGEVB Board Layout (1) Pattern design of the input capacitor Connect a capacitor near the IC for noise reduction between VIN and the GND. The change of current is at the largest in the pattern between an input capacitor and VIN as well as between GND and an input capacitor among all the main circuits. Hence make sure that the pattern is as fat and short as possible. (2) Pattern design of an inductor and the output capacitor High electric current flows into the choke coil and the output capacitor. Therefore this pattern should also be as fat and short as possible. (3) Pattern design with current channel into consideration Make sure that when High side MOSFET is ON (red arrow) and OFF (orange arrow), the two current channels runs through the same channel and an area is minimized. (4) Pattern design of the capacitor between VIN-PDR Make sure that the pattern of the capacitor between VIN and PDR is as short as possible. OUT (5) Pattern design of the small signal GND The GND of the small signal should be separated from the power GND. (6) Pattern design of the FB-OUT line Wire the line shown in red between FB and OUT to the output capacitor as near as possible. When the influence of noise is significant, use of feedback resistors R2 and R3 with lower value is recommended. FB Figure 9: FB-OUT Line 12 / 13 LV5980MC ON Semiconductor and the ON logo are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. 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