LV58063MC Step-Down Switching Regulator Application Note http://onsemi.com Overview LV58063MC is a 1ch step-down switching regulator. 0.13 FET is incorporated on the upper side to achieve high-efficiency operation for large output current. Low-heat resistance and compact-package SOP8L (200mil) employed. Current mode control gives superior load current response with easy phase compensation. EN pin, allowing the standby mode with the current drain of 70A. Pulse-by-pulse over-current protection and overheat protection available for protection of load devices. Externally adjustable soft start time. Function 3A 1ch step-down switching regulator Thermal shutdown Wide input range (8 to 28V) Reference voltage: 0.8V High efficiency (90% IOUT=1A, VIN=12V, VOUT=5V) Fixed frequency: 370kHz Standby mode Soft start Over-current protection Compact package: SOP8L (200mil) with exposed pad Overshoot control after over-current protection event SOP8L (200mil) Specifications Absolute Maximum Ratings at Ta = 25C Parameter Maximum input VIN voltage Symbol Conditions Ratings Unit VIN max BOOT pin maximum voltage VBT max SW pin maximum voltage VSW max BOOT pin-SW pin maximum voltage FB, EN, COMP, SS pin maximum 32 V 37 V VIN max V VBS-SW max 7 V Vfs max 7 V voltage Allowable power dissipation Pd max Junction temperature Tj max Operating temperature Storage temperature Mount on a specified board * 2.05 W 150 C Topr -20 to +80 C Tstg -40 to +150 C * Specified board: 46.4mm 31.8mm 1.7mm, glass epoxy. Note: Plan the maximum voltage while including coil and surge voltages, so that the maximum voltage is not exceeded even for an instant. Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. Semiconductor Components Industries, LLC, 2014 April, 2014 1/17 LV58063MC Application Note Recommended Operating Conditions at Ta = 25C Parameter Symbol Conditions Ratings Unit VIN pin voltage VIN 8 to 28 BOOT pin voltage VBT -0.3 to 34 V SW pin voltage VSW -0.4 to VIN V BOOT pin-SW pin voltage VBS-SW FB, EN, COMP, SS pin voltage VFSO V 6.5 V 6 V Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond the Recommended Operating Ranges limits may affect device reliability. Electrical Characteristics at Ta = 25°C VIN = 12V, unless otherwise specified. Parameter Symbol Conditions IC current drain in standby ICC1 EN=0V IC current drain in operation ICC2 EN=open, FB=1V Efficiency Effcy VIN=12V, IOUT=1A, VOUT=5V Design target: *1 Reference voltage Vref VIN=8V to 28V (2%) FB pin bias current Iref FB=0.8V application High-side ON resistance RonH BOOT=5V Low-side ON resistance RonL Oscillation frequency FOSC Oscillation frequency during FOSCS Ratings min typ -2% Unit max 70 A 5 mA 90 % 0.8 +2% V 10 100 nA 0.13 7 296 370 444 kHz 30 38 46 kHz 1.9 V short-circuit protection EN high-threshold voltage Venh EN low-threshold voltage Venl EN pull-up corrent Ien Maximum ON DUTY D max Current limit peak value Icl VIN=12V, VOUT=5V, L=10H Thermal shutdown temperature Ttsd Thermal shutdown temperature 0.8 V 16 A 80 % *Design guarantee *2 160 C Dtsd *Design guarantee *2 40 C ISS SS=0V EN=0V 3.8 A hysteresis Soft start current 6 10 14 A *1: Design target (not tested before shipment) *2: Design guarantee (value guaranteed by design and not tested before shipment) Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. 2/17 LV58063MC Application Note Package Dimensions unit : mm SOIC8 N EP / SOP8L (200 mil) CASE 751DM ISSUE O Allowable power dissipation, Pd max -- W 2.5 Pd max -- Ta Mounted on a specified board: 46.431.81.7mm3 glass epoxy both side 2.05 2.0 1.5 1.15 1.0 0.5 0 -20 0 20 40 60 80 100 Ambient temperature, Ta -- C 3/17 LV58063MC Application Note Pin Assignment BOOT 1 8 SS VIN 2 7 EN SW 3 6 COMP GND 4 5 FB Top view Block Diagram and Sample Application Circuit (3.3V output) BOOT (SW +Vreg.) BOOT C2=10F/25V + Current Sense Amp. Rb=0 R3=10k OSC 370kHz + Error Amp. + PWM comparator Pre-Drive SW D1=MBRA340 1:N R10=4.3k FB C8=10F/25V C1= 0.01F Pre-Drive UVLO R1=27k VIN=12V VOUT=3.3V L1=10H C5=22F/16V GND COMP C9=22F/16V R2=2.4k C3= 6800pF + Internal Stable SS supply EN Vref 0.8V VIN C6=0.015F H:ON or OPEN - Current Limit Logic C4=OPEN TSD Internal Regulator Internal Regulator (5V) L:OFF C1,C8,C5,C9 = Ceramic capacitor L1=CDRH105RNP-100NC (sumida) 4/17 LV58063MC Application Note Each function explanation 1. Calculation equation to set the output voltage (FB pin external resistor setting) This IC controls the switching so that the FB pin voltage becomes 0.8V(typ). The equation to set the output voltage is as follows: VOUT = Vref × {1 + (R1 + R10 ) (R1 + R10 ) } = 0.8 × {1 + } R3 R3 For example, if we want to set output voltage to be 12V, please use 10k For R3. 10k and 130k for R1 and R10. 5/17 LV58063MC Application Note 2. Standby Function (EN pin) When EN pin is applied low voltage, less than 1.2V(typical), the device will shut down all the circuits but EN pin monitoring internal bias circuit. When you apply high voltage to EN pin, the device will be activated and works switching regulator function. When EN pin is left open, the device is also activated the switching regulator function. Therefore, external NPN open collector drive or Nch MOS FET open drain drive to EN pin is recommended. EN pin has pull up current 16A typically at VIN=12V, EN=0V. So, the device will be activated, even if you left EN pin open. But, we recommend EN pin to be low until VIN voltage is applied and over 8V. ( Input Voltage, VIN, first, then activate EN pin ) 3. Soft start function LV58063 has soft start function. By using this function, the output voltage is ramped up which prevents input rush current and output voltage over shoot at start-up. This function is good also device itself, over current of the internal mos fet will be prevented and the electrical stress to the device will also be reduced. Please, connect a capacitor between the SS pin and GND. Soft start capacitor, C6 is given by next equation, TSS TSS C6 = ISS × V = 10 × 0.8 = 12.5u × TSS ref where, ISS : soft start current, TSS : soft start time, Vref : reference voltage, Example : soft start time = 1.2msec C6 = 12.5 × 1.2m = 0.015 [F] 4. Over Current Detection Function LV58063 is a peak current mode control type switching regulator. Output current is detected by the internal current sense amplifier. Current detection is performed with the drain voltage of the internal MOSFET, i.e., the voltage between a VIN terminal and SW terminal. In LV58063, over-current protection of the pulse By pulse system is performed by comparing the reference voltage value set to drain voltage inside. This over-current protection does not need to attach setting resistance etc. outside. Current limit value is fixed inside. When the current value of internal fixed is reached, it becomes an over-current of the pulse By pulse which turns off an output transistor. Furthermore, output current increases, by pulse By pulse over-current restrictions, output voltage declines and the voltage of FB terminal, If it becomes below 0.5V (TYP), switching frequency will usually be reduced to 32 kHz of about 1/10 at the time of an oscillation. This function is called the frequency fold back function. By reducing switching frequency, the average current from an input power supply is decreased, and the rise in heat of IC, a coil, and a Schottky diode is prevented. An over-current state is release, and if FB terminal voltage becomes more than 0.58V, switching frequency will return to usual 370 kHz. SS terminal voltage at the time of starting. Until it amounts to 1.9V (Ta = 25 C) Switching frequency is set to 370 kHz. It is only a time of SS terminal voltage becoming more than 1.9V after starting that the frequency fold back works. Starting smooth also at the time of starting is obtained. 6/17 LV58063MC Application Note Design Guide 1. Selection of the output Choke Coil The inductance value is computed as follows, according to the input voltage, the output voltage and the current ripple, ∆IR. Please, take the ripple current to be 20% or less of the maximum load current, as a guide value. For example, 3A maximum load current, the ripple current value is 0.6A. VIN - VOUT - Vsat × Ton ∆IR TT Ton = VIN - Vout - Vsat ( VOUT + VF ) + 1 L= Toff = T – Ton T : Repeated cycle of switching VF : Forward voltage of schottky diode Vsat : At switching transistor ON, saturated voltage (about 1.4V when the output current is 1A) VIN : Input voltage VOUT : Output voltage Inductor current: Peak value Please use the peak value of the ripple current within the ratings current value of the inductor. Inductor current peak value IRP is calculated by the following formula IRP = Iout + VIN - VOUT - Vsat × Ton 2L Inductor current: Ripple current value The ripple current ∆IR is calculated by the following formula. When the load current Iout is 1/2 ripple current or less, the current of the inductor becomes discontinuous. ∆IR = VIN - VOUT - Vsat × Ton L 7/17 LV58063MC Application Note 2. Selection of Output Capacitor Since large ripple current flows to the output capacitor, please, use the high frequency low impedance parts for output capacitor. And, please select ceramic capacitor or the tantalum capacitor whose equivalent series resistance (ESR) is small enough to clear your output ripple voltage. Since LV58063 is current control switching regulator, operation with ceramic capacitor, whose ESR is extremely small, is stable with easy compensation. The ripple current is a triangular waveform. The calculation formula is as follows. Please, select the output capacitor not to exceed the allowed ripple current value. IC2 = 1 VOUT ( VIN - VOUT ) × [Arms] L × Fsw × VIN 2 3 Fsw=switching frequency 370kHz 3. Selection of Input Capacitor Since the input current to the switching regulator is not continuous, (only when mos fet is on, the current flows from input node), The ripple current (half of the output current) that is larger than the output capacitor flows to the input capacitor. Therefore, it is necessary to note for the ripple current acceptable value as well as the output capacitor. Please select the capacitor of the ripple current allowance value that is larger than the ripple current value calculated by the following formula. IC1 ≥ D ( 1 - D ) × Iout [A] Ton D= T D means the time-ratio at turning on period. When this value is 0.5, the ripple current value becomes the maximum value. The current changing rate grows in the substrate wiring between the input capacitor to VIN and between the input capacitor to GND respectively. Please use a thick lead wire for the wiring so that the impedance becomes low. Refer to “PCB Layout “for further information. 4. Selection of Catch Diode The catch diode is subject to large peak and rms current stresses. Schottky diodes are recommended because of their low-forward voltage drop and the virtual absence of minority carrier reverse recovery. The catch diode used corresponds an average rectified output current of Iout = Ipeak/2 = 3A as provided in the specification. The catch diode rating must be at least 1.2 times greater than the maximum load current. The reverse voltage rating, on the other hand, should be at least 1.25 times in reference to the maximum input voltage. 8/17 LV58063MC Application Note Selection of compensation component 1.Frequency Characteristic of LV58063 Frequency characteristic of LV58063 is composed of following transfer functions. (1) Resistor divider for output voltage; HR (2) Gains of error amplifier, voltage gain; GVEA and current gain ( trans-conductance); GMEA (3) Impedance of external phase compensation components on COMP terminal; ZC (4) Current sense loop gain; GCS (5) Output filter impedance; ZO SLOPE OSC 1/GCS CLK GVEA GMEA Vref COMP Error amplifier L D Q ∆Vo ∆Vi VIN Current sense loop PWM comparator CLK C R VOUT SW CO CC RL R2 RC FB R1 HR fig. Current mode control loop of LV58063 Closed loop gain will be; G = HR × GMEA × ZC × GCS × Zo Vref 1 RL = V × GMEA × ( RC + C ) × GCS × 1 + C R O S C S O L you can see two poles and one zero in the closed loop gain of the converter. There is the first pole; fP1 which is composed of the output capacitor; CO and the load resistance; RL. 1 fP1 = 2πC R O L There is a zero; fZ which is composed of the external phase compensation network RC and CC. 1 fZ = 2πC R C C Lastly, the other pole fP2 is composed of output impedance of the error amplifier; ZEA and phase compensation capacitor, CC. 1 fP2= 2π×Z ×C EA C 9/17 LV58063MC Application Note 2.Determination of external phase compensation components; RC and CC. Requirement to get stable operation of switching regulator is, to set zero cross frequency; fZC at around 1/10 of the switching regulator oscillator frequency. (At the biggest, 1/5, if it is stable.) The switching regulator oscillator frequency of LV58063 is 370kHz, so, we shall set the zero cross frequency to be 37kHz. 370kHz 10 = 37kHz fZC= Zero cross frequency fZC is a frequency where amplitude of closed loop gain becomes unity (=1). So, Vref 1 RL G=V × GMEA × ( RC + C ) × GCS 1 + C R = 1 OUT S C S O L Where it is around zero cross frequency, 1 RC >> C S C Vref RL VOUT × GMEA × RC × GCS × 1 + 2π × fZC × CO × RL = 1 VOUT 1 1 1 + 2π × fZC × CO × RL ×G × RC = V × G RL ref MEA CS Therefore, where Vref=0.8 [V], GCS=6.2 [A/V], GMEA=900u [A/V] VOUT 1 1 1 + 2π × fZC × CO × RL RC = 0.8 × 900u ×6.2 × RL Example : VOUT=12V, COUT=30uF, RL=12ohm (IOUT=1A) 12 1 1 1 + 2 ×3.14 × 30u × 12 RC = 0.8 × 900u ×6.2 × ≈ 18.95k [] 12 This is the calculated compensation resistor value. If the zero frequency fZ and the pole frequency fP1 are same, the gain-phase characteristics of the converter will be single pole characteristics, where gain will be slope of -20dB/DEC, and phase is shifted only -90 degree, which is stable negative feedback is achieved. fZ = fP1 1 1 = 2πCCRC 2πCORL CC = RL×CO 12×30u RC = 18.95k ≈ 18.9n [F] i.e. RC = 18.95k [ohm] CC = 18.9n [F] These are the external phase compensation values, given by simple model explained above. With these values, we will start experimental study in your application to get stable operation in whole range of input voltage, temperature and transient response, to meet your requirement. Finally, we may change and determine external phase compensation values, Cc and Rc. Which is R2 and C3. We issue application board as a reference, to start your design on your board. 10/17 LV58063MC Application Note Noise reduction circuits (Snubber circuit and boot resistance) In order to reduce a noise, the Snubber circuit of CR series put in between SW-GND is effective. When the negative voltage under shot exceeding absolute maximum rating has appeared in SW terminal on your PCB board, a under shot can be pressed down in a Snubber circuit. In addition, the resistance Rb put into boot capacity in series can also stop the noise at the time of turn-on. Since the positive absolute maximum rating of SW terminal is VIN voltage, please use boot resistance and a Snubber circuit suitably to be used within absolute maximum rating on your PCB bard. If you connect bead to shottkey diode as a noise reduction means, there appears large negative voltage at SW terminal, which goes under the recommended operating voltage and it may lead to device destruction, so, please, do not use bead. We will recommend not shottkey bead but snubber circuit, C-R connection between SW and GND. Caution for designing PCB pattern layout A pattern design of board can change characteristics of DC-DC converter drastically. LV58063 switches high current at high speed. Therefore, the higher the inductance element of pattern layout is, the greater the risk for noise generation becomes. Hence, make sure that the pattern layout of the main circuit is as thick and short as possible. The followings are the caution for designing PCB layout. 1) Since high current flows into the current path when the power is ON ( input capacitor VIN pin upper MOS SW pin choke coil output capacitor input capacitor) and to the current path when the power is OFF (SBD choke coil output capacitor SBD), make sure that the pattern layout of the main circuit is as thick and short as possible. 2) FB pin and COMP pin controls output current. Make sure that SW pin for switching high current and its pattern and FB pin and COMP pin and its pattern are not adjacent to each other in the pattern layout. If it is inevitable, make sure to connect GND between them. 3) Make sure to connect a ceramic capacitor between VIN pin and GND (recommendation: 20F). Current when ON VIN SWpin IC: LV58063MC Current path when OFF SBD GND Input chip Ceramic Current when ON 11/17 LV58063MC Application Note How to use evaluation board 1) Please, connect external input power supply to VIN and GND[IN] terminal. 2) Please, connect your load between VOUT and GND[OUT]. 3) Turn on the input power supply, 3.3V is appeared on VOUT terminal. You can stop operation when turning off the input power supply. Also, you can stop converter operation, pulling down EN terminal voltage to low (Less than 1.25V). And, when EN terminal is open, converter operation is enabled. 1. Terminal Description VIN GND [IN] VOUT GND [OUT] SS EN Supply voltage input terminal Supply voltage ground terminal DC/DC converter output terminal DC/DC converter output ground terminal Soft start terminal Enable terminal. Hi or open will enable converter operation. Low will be stop operation. 2. Reference Evaluation Board (4-Layer) GND [OUT] terminal SS terminal VOUT terminal EN terminal Compensation Output setting Capacitor & Resistor Resistor GND [IN] terminal Output Ceramic Capacitor Soft start Capacitor Power Inductor VIN terminal Schottky Barrier Diode Input Ceramic Capacitor LV58063MC INPUT VOLTAGE OUTPUT VOLTAGE OUTPUT CURRENT Oscillation frequency SW terminal 24.0V 3.3V 3.0Amax 370kHz 3. 4-Layer Pattern layout 1Layer : IC + All parts 2Layer : VIN, PGND 12/17 LV58063MC Application Note 3Layer : SGND(IC pin_GND), IC Exposed PAD_GND 4Layer : PGND, FB, SS, EN 4. Schematic and Bill of materials DESIGNATOR PART NO. DESCRIPTION VALUE PACKAGE QTY VENDER NOTES C1 GRM188B11H Ceramic Capacitor 0.01uF 1608 1 MURATA 50Vdc, B C2 GRM32ER7YA Ceramic Capacitor 10uF 3225 1 MURATA 35Vdc, X7R C3 GRM188B11H Ceramic Capacitor 4700pF 1608 1 MURATA 50Vdc, B C5 GRM31CB31C Ceramic Capacitor 10uF 3216 2 MURATA 16Vdc, B C6 GRM188B11H Ceramic Capacitor 0.01uF 1608 1 MURATA 50Vdc, B R1 RK73H1J Resistor 27kΩ 1608 1 KOA F:1% R2 RK73H1J Resistor 2.2kΩ 1608 1 KOA F:1% R3 RK73H1J Resistor 10kΩ 1608 1 KOA F:1% R10 RK73H1J Resistor 4.3kΩ 1608 1 KOA Rb Resistor 0Ω 1608 1 KOA Inductor 10μH 10.3×10.5 1 sumida D1 RK73Z1J CDRH105RNP100NC MBRA340 SBD - - 1 ON SEMI IC LV58063MC IC - - 1 ON SEMI L1 F:1% Jumper Resistor Tmax=5.1mm, Rated Current=4.45A VRM=40V, IO=3A - 13/17 LV58063MC Application Note 5. Reference Characteristics Data ( VIN=24V, VOUT=3.3V, Ta=27deg ) 1. Efficiency – Load Current 2. Load Regulation 3. Load Regulation – Current limit 4. IC Surface Temperature Rise (IR thermometer) 5. Operate Waveform1 6. Operate Waveform2 ILOAD=0.1A (2s/div) CH1 : SW (10V/div) CH4 : IL (1.0A/div) ILOAD=1.2A (2s/div) CH1 : SW (10V/div) CH4 : IL (1.0A/div) 14/17 LV58063MC Application Note 7. Operate Waveform3 ILOAD=2.0A 8. Operate Waveform4 ILOAD=3.0A (2s/div) CH1 : SW (10V/div) CH1 : SW (10V/div) CH4 : IL (1.0A/div) CH4 : IL (1.0A/div) 9. Output Waveform1 ILOAD=0.1A (2s/div) 10. Output Waveform2 ILOAD=1.2A (2s/div) CH1 : VOUT (AC,20mV/div) (2s/div) CH1 : VOUT (AC,20mV/div) CH4 : ILOAD (0.5A/div) CH4 : ILOAD (0.5A/div) 11. Output Waveform3 ILOAD=2.0A 12. Output Waveform4 (2s/div) ILOAD=3.0A (2s/div) CH4 : ILOAD (0.5A/div) CH1 : VOUT (AC,20mV/div) CH1 : VOUT (AC,20mV/div) CH4 : ILOAD (0.5A/div) 15/17 LV58063MC Application Note 13. Load Transient Response1 ILOAD=1.5A <=>3.0A 14. Load Transient Response2 ILOAD=1.5A => 3.0A (100s/div) CH1 : VOUT (AC,50mV/div) (20s/div) CH1 : VOUT (AC,50mV/div) CH4 : ILOAD (1.0A/div) CH4 : ILOAD (1.0A/div) 15. Load Transient Response3 ILOAD=3.0A => 1.5A 16. Loop Gain and Phase ILOAD=3.0A,phase margin:θ=53deg(GAIN=0) (20s/div) CH1 : VOUT (AC,50mV/div) CH4 : ILOAD (1.0A/div) 17.Power On and Soft start Waveform ILOAD=1.2A (2.7Ω) (500s/div) CH1 : VIN (20V/div) 18.Power Off and Soft start Waveform ILOAD=1.2A (2.7Ω) (500s/div) CH1 : VIN (20V/div) CH2 : SS (1.0V/div) CH3 : VOUT (2.0V/div) CH4 : ILOAD (1.0A/div) CH2 : SS (1.0V/div) CH3 : VOUT (2.0V/div) CH4 : ILOAD (1.0A/div) 16/17 LV58063MC Application Note 19. EN High and Soft start Waveform ILOAD=1.2A (2.7Ω) (500s/div) 20. EN Low and Shutdown Waveform ILOAD=1.2A (2.7Ω) (500s/div) CH1 : EN (5.0V/div) CH2 : SS (1.0V/div) CH3 : VOUT (2.0V/div) CH4 : ILOAD (1.0A/div) CH1 : EN (5.0V/div) CH2 : SS (1.0V/div) CH3 : VOUT (2.0V/div) CH4 : ILOAD (1.0A/div) 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. 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