LC5720S APPLICATION NOTE LC5720S Application Note Rev.1.0 Rev.1.0 SANKEN ELECTRIC CO., LTD. http://www.sanken-ele.co.jp Copy Right: SANKEN ELECTRIC CO., LTD. Page.1 LC5720S APPLICATION NOTE Rev.1.0 CONTENTS General Descriptions ................................................................................................................. 3 1. Absolute Maximum Ratings ............................................................................................ 4 2. Recommended Operation Conditions............................................................................. 4 3. Electrical Characteristics ................................................................................................. 5 4. Functional Block Diagram ............................................................................................... 7 5. Pin Assign & Functions .................................................................................................... 7 6. Typical Application Circuit ............................................................................................. 8 7. Package Information ........................................................................................................ 9 8. Functional Description ................................................................................................... 10 8.1 PWM Current Control.......................................................................................... 10 8.2 LED Dimming ........................................................................................................ 11 8.3 Overcurrent Protection Function (OCP) ............................................................ 11 8.4 Overvoltage Protection Function (OVP) ............................................................. 12 8.5 Selection of application circuit ............................................................................. 12 8.6 Setting of External Inductor ................................................................................. 15 8.7 The Internal Power Dissipation Pd ...................................................................... 17 8.8 Phase Compensation (COMP terminal) .............................................................. 20 8.9 Peripheral Parts Design ........................................................................................ 22 8.10 Peripheral Parts Design ...................................................................................... 22 9. Example Pattern Layout ................................................................................................ 24 10. Design Considerations .................................................................................................. 26 IMPORTANT NOTES ........................................................................................................... 28 Copy Right: SANKEN ELECTRIC CO., LTD. Page.2 LC5720S APPLICATION NOTE General Descriptions Rev.1.0 Package SOP8 The LC5720S product is the power IC for LED driver which incorporates a power MOSFET and a controller IC in a package. This product is a DC/DC converter which features are; wide input voltage range, 500kHz operating frequency, and Buck/ Boost/ Buck-Boost converter can be selected with external circuit configuration. LED string current can be set with the external resistor, and LED dimming can be controlled by the digital input signal. The rich set of protection features helps to realize low component counts, and high performance-to-cost power supply. Characteristics Features Input voltage range Output current RDS(ON) Operation Types: The following converter types are applicable by the external circuit configuration ・Buck Converter ・Boost Converter ・Buck-Boost Converter High Efficienby: η > 90%(TYP) Operation Frequency: 500kHz(TYP) LED string current setting with an external resistor. Current Detection voltage of LED string: 100mV±5% Thus, low power loss and high accuracy LED string current can be achieved by setting of an external resistor. PWM Dimming Frequency: available to 20kHz(MAX) Package: HSOP8 Heat slag in the back can increase heat dissipation effect by connecting it to GND pattern Protection Functions ・Overcuurent Protection Function (OCP) ------ Pulse-by-pulse basis ・OvervoltageProtection Function (OVP) ------ Auto restart ・Thermal Shutdown Protection Function (TSD) ------ Auto restart 9.5V (MIN)~50V(MAX) 2A(MAX) 215mΩ(TYP) Applications LED lighting fixtures LED light bulbs Product name Lot Number(3digit) LC5720S SK YMW xxxx Y=The last digit of the year:(0 to 9) M= Month: (1 to 9,O=”10”,N=”11”,D=”12”) W=Manufacturing week: (1 to 5) Control Number(4digit) Copy Right: SANKEN ELECTRIC CO., LTD. Page.3 LC5720S APPLICATION NOTE Rev.1.0 1. Absolute Maximum Ratings Certain details refer to the specification sheet of this product. The polarity value for current specifies a sink as “+”, and a source as “−”, referencing the IC. Unless specifically noted, Ta is 25°C Table.1 Characteristic Pins Symbol Rating Unit VIN Pin Voltage 5-3 VIN −0.3 to 50.0 V SW Pin Voltage 4―3 VSW −0.3 to 50.0 V CSP Pin Voltage 6―3 VCSP −0.3 to 50.0 V CSN Pin Voltage Differential Voltage bwteen CSP and CSN Pins COMP Pin Voltage 7―3 VCSN −0.3 to 50.0 V 6―7 VCSP-CSN −0.3 to 5.5 V 1―3 VCOMP −0.3 to 5.5 V 8―3 VDIM −0.3 to 5.5 V (2) ― PD 1.35 W (3) ― TJ 125 °C (2) ― θj-a 74 ℃/W (1) ― Top −40 to 125 °C ― TSTG −40 to 150 °C DIM Pin Voltage Allowable Power Dissipation of MOSFET Junction Temperature in Operation Thermal Resistance (junction-ambient air) Operating ambient temperature Notes (1) Storage Temperature (1) However, it is limited by Junction temperature. (2) When mounted on a 40×40mm Glass-epoxy board (copper area in a 25×25mm). Non-movement (3) Thermal shutdown temperature is approximately 150°C 2. Recommended Operation Conditions Recommended Operation Conditions are the required operating conditions to maintain the normal circuit functions described in the electrical characteristics. In actual operation, it should be within these conditions. The polarity value for current specifies a sink as “+” and a source as “−” referencing the IC. Unless specifically noted, Ta is 25°C Table.2 Characteristic Pins Symbol MIN MAX Unit VIN Pin Voltage 5−3 VIN 9.5 50 V CSP Pin Voltage 6−3 VCSP 4.75 50 V ― Io 0 2 0 1 ― ∆IL - 0.8 Output current Peak to Peak Inductor Ripple current (4) A A Operating ambient (4) -40 +85 Top ― ℃ temperature (4) To be used within the allowable package power dissipation characteristics (fig. 1) (5) Buck circuit:2A, Boost circuit/Buckboost circuit:1A, ⊿IL ≦0.8A. Copy Right: SANKEN ELECTRIC CO., LTD. Page.4 Notes (5) Buck (5) Boost/Buckboost LC5720S APPLICATION NOTE Rev.1.0 3. Electrical Characteristics Certain details refer to the specification sheet of this product. The polarity value for current specifies a sink as “+” and a source as “−”, referencing the IC. Electrical Characteristics of Control Part (MIC) Unless specifically noted, Ta is 25°C, VIN=15V Characteristic Pins Symbol MIN TYP MAX Unit Operation Start Voltage 5−3 VIN(ON) 7.7 8.5 9.4 V Operation Stop Voltage 5−3 VIN(OFF) 7.2 8.0 8.9 V Operation Hysteresis Voltage 5−3 VIN(HYS) 0.1 0.3 0.5 V Circuit Current in Operation Circuit Current in None-Operation Operation Frequeny 5−3 IIN(ON) 3.0 4.5 7.0 mA 5−3 IIN(OFF) 400 600 1000 μA 4−3 fOSC 420 500 570 kHz Minimum On-Duty Cycle 4−3 tON(MIN) 50 75 100 ns VCOMP=0V Maximum On-Duty Cycle 4−3 DMAX 89 94 98 % VCOMP=4V On-Time1 4−3 tON(1) 300 600 800 ns VCOMP=0.7V On-Time2 4−3 tON(2) 0.85 1.4 1.8 μs 4−3 tCON 0.14 0.33 0.63 μs VCOMP=1.2V VCOMP=0.7V, ISW=2A Current Detection Voltage 6−7 VCS 95 100 105 mV CSP Pin Sink Current 6−3 ICSP 85 130 175 μA CSN Pin Sink Current 7−3 ICSN 40 65 95 μA CSP Pin Minimum Voltage 6−3 VCSP(MIN) 4.75 ― ― V COMP Pin Source Current 1−3 ICOMP(SRC −95 −60 −38 μA VCS=20mV, VCOMP=2V COMP Pin Sink Current 1−3 ICOMP(SNK) 38 60 95 μA VCS=180mV, VCOMP=2V ― gM ― 750 ― μs VCS=50 to 150mV 6−7 VCS(OVP) 200 240 280 mV 4−3 ISW(LIM) 2.5 3.5 4.7 A 4−3 RSW(L) ― 200 ― mΩ DIM Pin Voltage for LED On 8−3 VDIM(ON) 1.2 1.4 1.7 V DIM Pin Voltage for LED Off 8−3 VDIM(OFF) 0.75 1 1.2 V 8−3 VDIM(HYS) 0.3 0.5 0.7 V FDIM 32 ― 20000 Hz TJ(TSD) 150 160 ― °C TJ(TSDHYS) ― 20 ― °C On-Time for Current Contol (6) Error Amplifier Conductance Overvoltage Protection (OVP) Threshold Voltage SW Pin Current Limit SW Pin On-Resistance (6) DIM Pin Hysteresis Voltage (6) DIM Pin Dimming Frequency 8−3 Thermal Shutdown Activating (6) ― Temperature Thermal Shutdown Hysteresis (6) ― Temperature (6) Verified by design/characterization Copy Right: SANKEN ELECTRIC CO., LTD. Page.5 Notes VIN=6.5V ISW=1A LC5720S APPLICATION NOTE Allowable package power dissipation When mounted on a 40×40mm Glass-epoxy board (copper area in a 25×25mm). fig.1 Package power dissipation of LC5720S (Thermal Derating Curve) Note1 : The power dissipation in fig.1 is calculated at the junction temperature 125 ℃. Copy Right: SANKEN ELECTRIC CO., LTD. Page.6 Rev.1.0 LC5720S APPLICATION NOTE Rev.1.0 4. Functional Block Diagram fig.2 Block diagram 5. Pin Assign & Functions Table.4 COMP VDD NC CSN GND CSP SW Pin No. Symbol 1 COMP 2 NC 3 GND 4 SW 5 VIN 6 CSP 7 CSN 8 DIM Functions DIM EN/DIM VIN fig.3 Pin Assign Copy Right: SANKEN ELECTRIC CO., LTD. External phase compensation terminal. No-Connection Ground terminal. Switching Output. Switching node that drives the external inductor. Supply Input. Input capacitor CIN is connected between VIN and GND. Current Sense Input Positive. Reference potential for the current sense input. Current Sense Input Negative. Connect current sense resistor to sense output current. PWM Dimming Signal Input. Page.7 LC5720S APPLICATION NOTE Rev.1.0 6. Typical Application Circuit Examples for LED lighting power supply Input voltage 5 CIN VIN CSP 6 RCS LC5720S LC5700S CSN COUT 7 ROVP 8 LED DS DIM DZOVP 1 COMP CS CP SW GND 3 Output voltage 4 L RS fig.4-1 Buck converter Input voltage Output voltage Input voltage L 5 CIN VIN DS 6 CSP RCS LC5720S LC5700S COUT 7 CSN ROVP 8 1 DIM COMP CS CP GND 3 LED 4 SW DZOVP Output voltage RS fig.4-2 Boost converter Input voltage Output voltage Input voltage L DS CCSP 5 CIN VIN CSP 6 RCS LC5720S LC5700S CSN COUT 7 ROVP 8 LED DIM DZOVP 1 COMP CS CP GND 3 SW 4 Output voltage RS fig.4-3 Buck-Boost Converter Input voltage Output voltage Input voltage Copy Right: SANKEN ELECTRIC CO., LTD. Page.8 LC5720S APPLICATION NOTE Rev.1.0 7. Package Information HSOP8 8 7 6 5 1 2 3 4 Detail drawing of the A mark NOTES: 1) All dimensions are in Millimeter 2) Pb-free. Device composition compliant with the RoHS directive fig.5 Package outline Copy Right: SANKEN ELECTRIC CO., LTD. Page.9 LC5720S APPLICATION NOTE Rev.1.0 8. Functional Description All of the parameter values used in these descriptions are typical values of the electrical characteristics, unless they are specified as minimum or maximum. With regard to current direction, “+” indicates sink current (toward the IC) and “–” indicates source current (from the IC). 8.1 PWM Current Control The current control circuit is shown in fig.6. CS RS 1 Osillator COMP + CSP 6 RCS - ROVP - Q S + - External components CSN 7 VCS LED COUT Output voltage R SW 4 + + Σ - fig.6 Current control circuit For enhanced response speed and stability, current mode control (peak current mode control) is used for constant current control of the output current. The operating frequency, fOSC, is fixed to 500kHz. LED string current is detected by the current detection resistor, RCS. The voltage of RCS is detected by both CSP and CSN pins. This IC compares this voltage with the Current Detection Voltage, VCS, and makes a target value for current control. The constant current is controlled so that the detection voltage of peak current of internal power MOSFET is close to the target value, and thus the LED string current is constant. The constant current of LED string, IOUT, is calculated by the following with RCS as the current detection resistor and ROVP as the resistor for overvoltage protection in the case that LED string is open. IOUT where; VCS ICSN (RCS ROVP) RCS ・・・(1) ICSN : the CSN Pin Sink Current, 9.5μA. VCS : the Current Detection Voltage, 100mV. Also, IOUT can be expressed by the following, if ICSN×(RCS+ROVP) is negligibly small against VCS. IOUT VCS RCS ・・・(2) ROVP value should be chosen so that IOUT is within the acceptable accuracy range referring to the calculation in “8.4 Overvoltage Protection Function (OVP)”. Copy Right: SANKEN ELECTRIC CO., LTD. Page.10 LC5720S APPLICATION NOTE Rev.1.0 8.2 LED Dimming LED dimming is controlled by the duty cycle of PWM digital signal which is input to DIM pin. The constant current output turns ON/OFF by the following signal input voltage to DIM pin which is within the absolute maximum rating; −0.3V to 5.5V. ・When DIM Pin Voltage for LED On, VDIM(ON)= 1.4V or more is input, IOUT flows. ・When DIM Pin Voltage for LED Off, VDIM(OFF)= 1V or less is input, IOUT stops. The constant current value is controlled with the current detection resistor, R CS, and the current detection voltage, VSC. When DIM pin voltage is less than VDIM(ON), COMP pin voltage is held with the fixed voltage, and when DIM pin voltage is more than VDIM(ON), COMP pin voltage is increased from this hold voltage. This makes the constant current startup speed fast at DIM dimming. The Dimming-ratio depends on the duty ratio of the PWM-digital-dimming signal pulse (fig.7). PWM Dimming with 1kHz, Duty 50% PWM Dimming with 1kHz, Duty 25% CH2: Dimming signal (2V/div) CH3: LED current (0.2A/div) CH1: SW pin voltage (10V/div) PWM Dimming with 1kHz, Duty 75% fig.7 PWM Dimming with Duty 100% Actual waveform in Dimming operation 8.3 Overcurrent Protection Function (OCP) The IC incorporates Overcurrent Protection Function (OCP) limited the current flowing to SW terminal (fig.8). When the current to SW terminal reaches ISW(LIM)= 3.5A, the internal power MOSFET turns off on pulse-by-pulse basis.This protection is activated in case of the constant current detection failure or the output end shorted. SW 4 PWM LOGIC + OCP - GND 3 fig.8 Overcurrent protecton circuit Copy Right: SANKEN ELECTRIC CO., LTD. Page.11 LC5720S APPLICATION NOTE Rev.1.0 8.4 Overvoltage Protection Function (OVP) If LED string is open and the constant current loop is cut, the output voltage increases more than the controlled voltage. As shown in fig.9, the OVP Function with the circuit connected ROVP and a zener diode, DZOVP, is done OVP protection. After LED string is open, when DZOVP is conducted, the output voltage is limited to the sum voltage of the zener voltage of DZOVP and the Overvoltage Protection (OVP) Threshold Voltage, VCS=240mV. CSP 6 RCS ICSN CSN CSP COUT 7 CSN 6 RCS ICSN 7 ROVP COUT ROVP IDZ IOUT DZOVP DZOVP LED Normal operation fig.9 LED string is open Overvoltage protection circuit The allowable current of DZOVP, IDZ, can be expressed by the following with PDZ as the allowable dissipation and VDZ as the zener voltage of DZOVP. IDZ PDZ VDZ ・・・(3) The ROVP value, by which the loss of DZOVP is less than the allowable dissipation, is chosen by the following with ICSN as the CSN Pin Sink Current and RCS as the constant current detection resistor. ROVP VCS ( OVP) RCS IDZ ICSN ・・・(4) Also, when ICSN is negligibly small against IDZ, the approximate equation of Equation (4) becomes as follows. ROVP VCS ( OVP) RCS IDZ ・・・(5) ROVP value should be chosen so that the loss of DZOVP is less than the allowable dissipation in OVP protection, and IOUT is within the acceptable accuracy range. DZOVP value, VDZ, should be chosen to be higher than the maximum output voltage of LED string to avoid DZ OVP conduction during the normal operation. 8.5 Selection of application circuit Select application circuit properly in the relations with the LED strings voltage and the input voltage VIN in the Table 6. Table.6 Relations between the input voltage and the LED string voltage . VIN>(n × VFLED)+Vcs VIN<(n × VFLED)+Vcs VIN(Low)<(n × VFLED)+Vcs<VIN(High) Circuit type Buck Boost Buckboost The number of LED which can be serial connection in LC5710S becomes as follows in the Table 7 in each circuit type. But, there are the following 1) - 4) as a factor which a movement condition is restricted to. Copy Right: SANKEN ELECTRIC CO., LTD. Page.12 LC5720S APPLICATION NOTE Rev.1.0 1) Settlement of the input voltage under VIN (ON) ・・・The setup that VIN is under 9.5V is impossible by the start condition of the IC. 2) VIN(MAX) or Vsw(MAX) ・・・As an example, the condition that VIN or Vsw voltage reaches 40V by 80%-derating against 50V which is the absolute maximum ratings. 3) A limitation (0.05<Duty<0.89) by the minimum or maximum ON-duty. 4) The input and output condition that "Inductor peak current ILp" reaches threshold of "SW current limit ISW (LIM) =2.5A (Min)" . Table.7 VIN(or Vsw)<40V(50V×0.8), 0.05<Duty<0.89 are common condition. Range of the VIN(V) Number of Vout or Buck-type Boost-type Buckboost-type LED (pcs) (Serial connection) LED strings voltage(V) 1 2 3 4 5 6 7 8 9 10 11 3.6 7.1 10.6 14.1 17.6 21.1 24.6 28.1 31.6 35.1 38.6 ILED=2.0A,⊿IL=0.8A ILED=1.0A,⊿IL=0.4A ILED=1.0A,⊿IL=0.4A MIN(V) 9.50 9.50 11.91 15.84 19.78 23.71 27.64 31.57 35.51 39.44 MIN(V) MAX(V) 9.50 9.50 9.50 10.30 11.80 13.40 15.20 16.80 18.40 10.07 13.40 16.72 20.05 23.37 26.70 30.02 33.35 36.67 MIN(V) 9.5 9.5 9.5 10.9 13.6 16.3 MAX(V) 40.00 40.00 40.00 40.00 40.00 40.00 40.00 40.00 40.00 40.00 MAX(V) 36.4 32.9 29.4 25.9 22.4 18.9 For non ・・・In case of following condition, VIN under VIN (ON), VIN or Vsw reaches 40V, and ILp reaches ISW(LIM), it is the setup which doesn't become utility. When a table 7 is graphed, they are shown in the fig10 – the fig12. Number of LEDs serial connection n(pcs) Buck-type Number of LEDs serial connection vs.Range of VIN ×10 ×9 ×8 ×7 ×6 ×5 ×4 ×3 ×2 ×1 0 5 10 15 20 25 30 Input voltage VIN(V) fig.10 Copy Right: SANKEN ELECTRIC CO., LTD. Page.13 35 40 45 LC5720S APPLICATION NOTE Rev.1.0 Number of LEDs serial connection n(pcs) Boost-type Number of LEDs serial connection vs.Range of VIN ×11 ×10 ×9 ×8 ×7 ×6 ×5 ×4 ×3 ×2 ×1 0 5 10 15 20 25 30 Input voltage VIN(V) 35 40 45 fig.11 Number of LEDs serial connection n(pcs) Buckboost-type Number of LEDs serial connection vs.Range of VIN ×6 ×5 ×4 ×3 ×2 ×1 0 5 10 15 20 25 30 35 40 45 Input voltage VIN(V) fig.12 The fig12 – the fig14 are based on the calculation. You must reduce ILED,frequency and Vout when surge voltage is big in the waveform of the SW terminal, and when the heat generation of the IC is high. And, you must use it within the range of “Thermal Derating Curve” of the fig1. Copy Right: SANKEN ELECTRIC CO., LTD. Page.14 LC5720S APPLICATION NOTE Rev.1.0 8.6 Setting of External Inductor The each operation of Buck, Boost and Buck-Boost converter is explained as follows. The inductance value is designed so that the operation becomes Continuous Conduction Mode (CCM) which the inductance current flows continuously, because the load current of LED lighting application is constant. The duty, D, is set within the following range, based on “3. Electrical Characteristics”. tON(MIN)×FOSC < D <DMAX ・・・(6) Therefore, Duty-D is within the range of 0.89 from 0.05 ( 0.05< D <0.89). The output voltage, VOUT, can be calculated by the following with VOUT as the output voltage, IL as the inductor current, and ΔIL as the ripple current of inductor current. Vout= n×VFLED+VCS ・・・(7) where; VFLED : Forward voltage drop of a LED(・・・VF=3.5V/1PCS) n : The number of LED in series VCS : Current Detection Voltage, VCS= 100mV Table.8 Equations to calculate Necessary Inductance L Buck type Boost type Buckboost type VIN Vout VIN+Vout SW terminal voltage Vsw ON-duty “D” + Inductor average current ILAVE ILED Inductor peak current ILp + Necessary Inductance L ⊿ ⊿ + ⊿ ⊿ + ⊿ ⊿ In case of Buck-type, as for the Drain-current which flows into the SW terminal, Drain-current becomes equal to LED current. But, in case of Boost-type, or in case of Buckboost-type, for example when the Duty-D is 0.5, if it is same inductor-ripple current, Drain-current is doubled from Buck-type. Be careful to this point. Inductor-ripple-current is "⊿IL=0.8A(Max)", it is based on a recommendation. And, by the condition of internal-over-current-protection, because it is required that Inductor-peak-current “ILp” doesn't reach "ISW (LIM) =2.5A (MIN)". Substantially, the current which can be supplied to LED becomes as follows (you must satisfy together a temperature limitation referring to the fig.1). *Buck- type ・・・ 2.0A ,⊿IL=0.8A(Max) *Boost-type/Buckboost-type ・・・ 1.0A ,⊿IL=0.4A(Max) A calculation example graph is shown as follows (Refer to the fig13- the fig15). And, a VF of white-LED for the lighting is prescribed with 3.5V, and calculated with 5pcs series-connection (Vout=17.6V). Copy Right: SANKEN ELECTRIC CO., LTD. Page.15 LC5720S APPLICATION NOTE Rev.1.0 Buck-type Necessary Inductance L calculation example LED=5pcs series,VIN=24V Necessary Inductance L(μH) 100 10 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Inductor-ripple current ⊿IL(A) fig.13 Boost-type Necessary Inductance L calculation ezample LED=5pcs series,VIN=12V Necessary Inductance L(μH) 100 10 1 0.1 0.15 0.2 0.25 0.3 Inductor-ripple current⊿IL(A) fig.14 Copy Right: SANKEN ELECTRIC CO., LTD. Page.16 0.35 0.4 LC5720S APPLICATION NOTE Rev.1.0 Buckboost-type Necessary Inductance L calculation example LED=5pcs series,VIN=Vout±20% Necessary Inductance L(μH) 1000 fig13-fig15 Necessary Inductance L calculation example *FOSC = 500kHz *Number of LED = 5pcs series The value of graph is calculated following the equation in the Table8. 100 10 1 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Inductor-ripple current⊿IL(A) fig.15 Note: *Necessary inductance value grows big by the setup whose “⊿IL is small”. As a tendency of characteristics of the Inductor, ・In case of big Inductance value, allowable current limits decrease. ・The contour of Inductor becomes large with the core size when allowable current is satisfied and Inductance is kept. As a circuit application of the LED driver, it has Buck-type, Boost-type and Buckboost-type as same as the DC/DC converter, As a setup of ⊿IL, generally, it is said that the cost performance of 20%-30 % of the setups of output current is the best. When it says easily,"⊿IL=Iout×α(α=0.2 to 0.3)" is best choice. 8.7 The Internal Power Dissipation Pd 8.7.1 The loss Pcont of the control circuit The loss Pcont of the control circuit depends on the input voltage and frequency. (fig.16) . The loss of control circuit Pcont(mW) LC5720S VIN vs. Pcont characteristics 450 400 350 300 250 200 150 100 50 0 0 5 10 15 20 25 30 35 40 45 50 Input Voltage VIN(V) fig.16 The loss of the control circuit is prescribed with containing the steady loss by circuit static electric current Iq and the drive loss which drives internal PowerMOSFET. A fig.16 is the total of the loss of circuit electric current and the drive loss. Read near value in the fig.16, and substitute it when you calculate a loss. Copy Right: SANKEN ELECTRIC CO., LTD. Page.17 LC5720S APPLICATION NOTE Rev.1.0 8.7.2 The switching-speed of internal PowerMOSFET As for the fig.17, in the calculation of the switching-time of internal PowerMOSFET, this is based on the assumption with no influence such as Prasitic-Inductance in main-circuit. It is prescribed with "turn-on time tr" and "turn-off time tf" being the same speeds. The switching time(Tsw:tr,tf) (nsec) LC5720S SW terminal voltage vs. Tsw characteristics 80 70 60 50 40 30 20 10 0 0 5 10 15 20 25 30 35 40 45 50 SW terminal voltage Vsw(V) fig.17 However,actually,The internal PowerMOSFET is connected with the main-circuit of the voltage conversion part. By the condition of pattern wiring, the switching-speed becomes fast, or becomes slow. ・In case of the pattern which Parasitic-Inductance inheres in, probably it becomes fast. ・In case of the pattern which high-impedance inheres in, probably it becomes slow. Approve it in advance. There is no problem if actual measurement value is substituted when an actual movement wave form can be observed with oscilloscope and so on. 8.7.3 The loss of internal PowerMOSFET . As the loss of internal-PowerMOSFET, there are the loss of "steady-ON" by the ON-resistance "Ron" between the "source" and "drain", and the switching-loss by the switching-time in the fig.17. Buck-type, Boost-type and Buckboost-type, the loss of PowerMOSFET of each type are shown the approximation in the Table9. Table.9 Loss of “Steady-ON” Pon Switching loss Psw Buck type Ron×(ILED)2×Ton×Fosc 2×{VIN×(ILED/2)×Tsw×Fosc} Boost type Ron×(ILAVE)2×Ton×Fosc 2×{Vout×(ILAVE/2)×Tsw×Fosc} Buckboost type Ron×(ILAVE)2×Ton×Fosc 2×{(VIN+Vout)×(ILAVE/2)×Tsw×Fosc} * ・Ton=(1/Fosc)×D・・・D=Duty (Refer to Table7.) ・Tsw is prescribed by the value (sec) of the fig19 with "turn-on time tr" and "turn-off time tf" being the same speeds. In the same period, switching occurs twice. There is no problem if actual measurement value is substituted when an actual movement wave form can be observed with oscilloscope and so on. ・Fosc= oscillating frequency (Hz) ・In case of the Buck-type, ILED(A)=ILAVE(A) ・Refer to a Table 7 for ILAVE (A). ・Ron is "ON-resistance(Ω)" of the internal PowerMOSFET, between drain and source. Copy Right: SANKEN ELECTRIC CO., LTD. Page.18 LC5720S APPLICATION NOTE Rev.1.0 8.7.4 Power dissipation in the IC, Pd The internal loss is to follow a equation (8). Pd=Pcont+Pon+Psw ・・・(8) (Calculation example in the Buck-type) Conditions:Fosc=500kHz、VIN=24V、LED strings voltage=17.6V(5LEDs)、ILED=2A、Ron=0.215Ω. ・Pcont=200mW (It was referred from fig.16.) ・Pon=0.215(Ω)×1(A)×1(A)×1.46E-6(sec)×500E+3(Hz) ≒0.157W ・Psw=2×{24(V)×(1(A)/2)×35E-9(sec)×500E+3(Hz)} ≒0.42W ∴Pd=0.2(W)+0.157(W)+0.42(W) =0.777W (Calculation example in the Boost-type) Conditions:Fosc=500kHz、VIN=12V、LED strings voltage=17.6V(5LEDs)、ILED=1A、Ron=0.215Ω. ・Pcont=100mW (It was referred from fig.16.) ・Pon=0.215(Ω)×1.467(A)×1.467(A)×0.636E-6(sec)×500E+3(Hz) ≒0.147W ・Psw=2×{17.6(V)×(1.467(A)/2)×25E-9(sec)×500E+3(Hz)} ≒0.322W ∴Pd=0.1(W)+0.147(W)+0.322(W) =0.567W (Calculation example in the Buckboost-type) Conditions:Fosc=500kHz、VIN=17V、LED strings voltage=17.6V(5LEDs)、ILED=0.5A、Ron=0.215Ω. ・Pcont=140mW (It was referred from fig.16.) ・Pon=0.215(Ω)×1.018(A)×1.018(A)×1.016E-6(sec)×500E+3(Hz) ≒0.113W ・Psw=2×{(17(V)+17.6(V))×(1.018(A)/2)×48E-9(sec)×500E+3(Hz)} ≒0.422W ∴Pd=0.14(W)+0.113(W)+0.422(W) =0.675W Notes: The thermal resistance θj-a of the package is becomes 74(℃/W). Thermal shutdown( protection function:TSD) may activate by the condition of Pd. When ambient temperature is defined as “Ta”, Junction temperature “Tj” is shown with a equation (9). Tj=(Pd×θj-a)+Ta ・・・(9) The "ON-resistance" Ron of internal PowerMOSFET has a positive temperature coefficient. When Tj is nearing 100(℃) , Ron has the possibility to increase about 1.5 times from condition of Tj=25(℃). *Be careful. When temperature of the IC is high, you must have the following item reduced. ・Oscillating frequency ・Value of the ILED ・The number of LED serial connection Or, you must establish the input voltage condition again, you must put Pd within the area of “Thermal Derating Curve” in the fig.1. Copy Right: SANKEN ELECTRIC CO., LTD. Page.19 LC5720S APPLICATION NOTE Rev.1.0 8.8 PHASE COMPENSATION (COMP terminal) 8.8.1 The calculation of the Phase compensation "fixed-number" . In the fig.4 of sixth clauses – Typcal application circuit example, as for the Phase-compensation fixed-number of the COMP terminal connection, "Rs, Cs, Cp", they are calculated in accordance with the equation of the Table10. Table.10 Rs Cp Cs Requirement decision (←When a left equation satisfies a condition.) Cp RLed Fz2 Fc of the Buck-type Fc of the Boost-type *Co : Capacitance of output capacitor (F), Vout : Output voltage (V), Fc : Crossover frequency (Hz), ESR : The equivalent serial resistance of the output capacitor (Ω), RLed : The resistance when LED was considered a resistance load (Ω), ILED : Average current of LED (A), Fz2 : The zero point frequency which is characteristic of Boost-type (Hz) ・・・ This does the function of the zero in the gain-characteristics, and this does the function of the pole in the phase-compensation. L : Inductance of the main inductor (H), D : Duty (On-period/period of a cycle), refer to Table7. *Cp is necessary because ESR is big when a output capacitor COUT is aluminum electrolytic capacitor. The setup of crossover-frequency Fc is different in the Buck-type and the Boost-type.Usually, at the case of Buck-type, Fc is set up in less than 1/10 of Fosc. But, it has the condition of 'a righthalf plane zero' in case of Boost-type of the Current-Mode. Therefore you must calculate Fz2 by the equation of Fz2 of the Table9, and you must set up Crossover-frequency Fc in less than 1/10 of Fz2. *” K” is the multiplier which is characteristic of the feedback loop of LC5720S. K=2.497E-4 8.8.2 Rs,Cs, calculation example (COUT: ceramics capacitor) Table.11 Buck-type ,Fosc=500kHz, ILED=2A, ⊿IL=0.8A Number Inductanc Co total of LED Vout(V) VIN(V) eL capacitance( serial connection 1 2 3 4 5 6 7 8 9 3.6 7.1 10.6 14.1 17.6 21.1 24.6 28.1 31.6 5 12 15 18 24 28 33 36 40 Co total ESR (μ H) μ F) (mΩ ) 2.7 7.5 8.2 8.2 12 15 18 18 18 1 1 1 1 1 1 1 1 1 10 10 10 10 10 10 10 10 10 Fc(kHz) Rs(kΩ ) Cs(pF) 50 50 50 50 50 50 50 50 50 4.53 8.93 13.33 17.73 22.13 26.53 30.93 35.34 39.74 2814 1427 956 719 576 480 412 361 321 *The numerical value in the table shows value in calculation. *Select a part from the near fixed-number , because numerical value doesn't agree completely in the geometric progression such as E12 series and E24 series. * Decide a fixed-number after you surely confirm a movement in the experiment. *The capacity of Cout and ESR are the expressions of 'the total'. When Ceramics capacitor of the little size more Copy Right: SANKEN ELECTRIC CO., LTD. Page.20 LC5720S APPLICATION NOTE Rev.1.0 than one are connected in parallel , it is shown that it becomes the numerical value of the table in the total. *Table12 is the same situations,too. Table.12 Boost-type, Fosc=500kHz, ILED=1A, ⊿IL=0.4A Number Inductanc Co total of LED Vout(V) VIN(V) eL capacitance( serial connection 2 3 3 4 4 5 6 6 7 7 7 8 8 9 10 7.1 10.6 10.6 14.1 14.1 17.6 21.1 21.1 24.6 24.6 24.6 28.1 28.1 31.6 35.1 5 5 7 7 9 12 12 15 12 15 18 15 18 18 24 Co total ESR (μ H) μ F) (mΩ ) 7.5 15 12 18 18 20 27 22 33 33 27 36 33 39 39 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 Fc(kHz) Rs(kΩ ) Cs(pF) 14.952 5.007 12.268 6.149 10.164 13.028 8.05 15.436 5.649 8.827 15.535 7.083 11.127 8.373 13.401 2.67 1.33 3.27 2.18 3.6 5.77 4.27 8.19 3.5 5.46 9.61 5.01 7.86 6.65 11.83 15956 95286 15874 47510 17387 8478 18523 5037 32259 13214 4266 17962 7279 11433 4018 *In theBuckboost-type, Relations between "Duty D" and the movement mode are as the following. D>0.5:Boost mode D<0.5:Buck mode Referring to the Table11 - the Table12, adjust compensation value in accordance with the condition of the use, under the actual movement . Copy Right: SANKEN ELECTRIC CO., LTD. Page.21 LC5720S APPLICATION NOTE Rev.1.0 8.9 Peripheral Parts Design Take care to use properly rated and proper type of components. The following circuit symbols refer to “6. Typical Application Circuit”. Inductor L This is a choke coil for smoothing LED current. When the indactance is larger, the output ripple current is smaller, and the current stability is improved. In actual operation, it should be considered so that the coil is not saturated by the peak of ripple current. If the coil is saturated, the surge current beyond expectations flows. Thus LED, IC and peripheral circuit will be damaged. Diode DS This is a free-wheel diode for Buck converter, and this is a boost diode for Boost and Buck-Boost converter. For diode selection, the withstanding voltage and the recovery time (trr) are important. In case that diode with a long trr is used, the large surge current flows into power MOSFET when power MOSFET turns on. Thus, it may cause noise increasing, malfunction and efficiency decreasing. It is recommended to choose from Schottky barrier diode and Ultra-fast diode according to the withstanding voltage. Current detection resistor RCS If the current detection resistor with high inductance is used, it may cause malfunctioning because of the high frequency current flowing through it. It is recommended to choose a low equivalent series inductance and high surge tolerant type for the current detection resistor. Input capacitor CIN This is a smoothing capacitor for main power supply. When the capacitance is larger, the ripple voltage is smaller. It is recommended to choose the capacitance according to the output power because the ripple voltage becomes bigger when the output power increases even if the same capacitance. Output capacitor COUT By the ipple current specification of LED string, it is recommended to determine whether COUT is needed or not, or to determine the capacitance value. If large ripple current can be set, the inductance of L can be smaller, the COUT capacitance can be smaller or the COUT can be removed. Thus, the power supply will be downsized and reduced the cost. If the small ripple current is set, the inductance of L is increased or COUT is connected in parallel with LED string. Thus, the heat generation of LED string, which is caused by ripple current variation, can be reduced. In addition, if LED string is far from the output edge of power supply, COUT is connected close to LED string in parallel so that the ripple voltage and ripple current can be reduced. Phase compensation network CP, CS, RS These are the "phase compensation parts" of a control-loop to connect to the COMP terminal. Connect the GND side of the "phase compensation parts" to GND Pin of the IC at shortest wiring. When it is far from GND of the IC, noise appears in the COMP terminal by the influence such as parasitic-inductance of the pattern, and the faulty operation occurs often. Be careful. Copy Right: SANKEN ELECTRIC CO., LTD. Page.22 LC5720S APPLICATION NOTE Rev.1.0 8.10 Reference Design Example (A)Buck-type Fosc=500kHz ILED=2A Inductor ripple current ⊿IL=0.8A Number of LED=5LEDs(Vout=17.6V) VIN=24V Vsw=24V Cout(ESR)=10mΩ/ceramics capacitor Cp(C4):Open *SJPB-L6 being used as the D1 is manufactured by "Sanken-electric Co". (B)Boost-type Fosc=500kHz ILED=1A Inductor ripple current ⊿IL=0.4A Number of LED=7LEDs(Vout=17.6V) VIN=12V Vsw=17.6V Cout(ESR)=10mΩ/ ceramics capacitor Cp(C4):Open *SJPB-L6 being used as the D1 is manufactured by "Sanken-electric Co". (C)Buckboost-type Fosc=500kHz ILED=1A Inductor ripple current ⊿IL=0.4A Number of LED=5LEDs(Vout=17.6V) VIN=17V Vsw=34.6V Cout(ESR)=10mΩ/ ceramics capacitor Cp(C4):Open *SJPB-L6 being used as the D1 is manufactured by "Sanken-electric Co". *The above reference design example is only a guide. Decide the fixed-number on your circuit board after you confirm a movement in the actual working,experiment adjustment. fig.18 (a) - (c) Reference design example Copy Right: SANKEN ELECTRIC CO., LTD. Page.23 LC5720S APPLICATION NOTE Rev.1.0 9. Example Pattern Layout For the LC5710S,the LC5711S and the LC5720S, the circuit board pattern of demonstration-board by our company is shown in the following. manufactured 9.1 pattern layout For Buck-type (parts mounting side) For Buck-type(back side) For Boost-type/Buckboost-type (parts mounting side) For Boost-type/Buckboost-type(back side) fig.19 Demo-board pattern layout *Foot print drawing fig.20 Footprint drawing for LC5720S Copy Right: SANKEN ELECTRIC CO., LTD. Page.24 LC5720S APPLICATION NOTE Rev.1.0 9.2Circuit diagram of Demonstration-Board 9.2.1 For Buck-type J1 fig.20 *LC5710S/LC5720S : R5 and R6 must be open. Jumper-J1 must be inserted. C7 and R7 are used only with LC5710S. 9.2.2 For Boost-type and Buckboost-type J2 J1 fig.21 *The setup of Jumper For Boost-type: J1= Insert, J2= Open For Buckboost-type: J1= Open, J2= Insert * C7 and R7 are used only with LC5710S. Copy Right: SANKEN ELECTRIC CO., LTD. Page.25 LC5720S APPLICATION NOTE Rev.1.0 10. Design Considerations Trace and Component Layout Design PCB circuit trace design and component layout affect IC functioning during operation. Unless they are proper, malfunction, significant noise, and large power dissipation may occur. Circuit loop traces flowing high frequency current, as shown in fig.22, should be designed as wide and short as possible to reduce trace impedance. In addition, earth ground traces affect radiation noise, and thusshould be designed as wide and short as possible. Switching mode power supplies consist of current traces with high frequency and high voltage, and thus trace design and component layout should be done in compliance with all safety guidelines. Furthermore, because an integrated power MOSFET is being used as the switching device, take account of the positive thermal coefficient of RDS(ON) for thermal design. (B)Boost-type (A)Buck-type (C)Buckboost-type fig.22 High frequency current loops(hatched portion) fig.23 shows practical trace design examples and considerations. In addition, observe the following: IC peripheral circuit (1) Main Circuit Traces Main circuit traces carry the switching current; therefore, widen and shorten them as much as possible. The loop formed with CIN, VIN pin, and GND pin should be small in order to reduce the inductances of the traces against high frequency current. (2) Traces around GND pin Main circuit GND and Control circuit GND should be connected to the vicinity of GND pin with dedicated traces respectively, in order to avoid interference of the switching current with the control circuit. (3) Traces around the current detection resistor, RCS The traces of RCS should be connected to CSP pin and CSN pin with dedicated traces respectively, in order to reduce noises when the current is detected. When the noise between CSP and CSN is high, a filter capacitor Cf can be added like a "Page8, sixth clauses-application circuit example",too. (4)Peripheral components The components for phase compensation such as C P, CS, RS should be connected close to COMP pin and GND pin. (5) When COUT is used, it should be connected close to LED string. * As for the GND pattern, be careful that routes for the Main-circuit(switching current flows), and the routes for the small-signal don't become common impedance. Copy Right: SANKEN ELECTRIC CO., LTD. Page.26 LC5720S APPLICATION NOTE Rev.1.0 (A)Buck-type Input voltage 5 VIN CIN CSP LC5720S LC5700S RCS DS CSN 8 6 ROVP 7 DIM COUT LED DZOVP 1 COMP CS CP GND 3 SW Output voltage 4 L Main circuit GND of Control circit RS (B)Boost-type Input voltage DS L 5 CIN VIN CSP 6 RCS LC5720S LC5700S CSN ROVP 7 LED COUT 8 DIM 1 COMP CS SW GND 3 4 Output voltage DZOVP Main circuit GND of Control circit RS (C)Buckboost-type Input voltage DS L 5 VIN CSP RCS LC5720S LC5700S CIN CCSP 6 CSN ROVP 7 COUT 8 DIM 1 CS COMP DZOVP GND 3 SW 4 Output voltage RS Fig.23 The trace of the pattern Copy Right: SANKEN ELECTRIC CO., LTD. LED Page.27 Main circuit GND of Control circit LC5720S APPLICATION NOTE Rev.1.0 IMPORTANT NOTES The contents in this document are subject to changes, for improvement and other purposes, without notice. Make sure that this is the latest revision of the document before use. Application and operation examples described in this document are quoted for the sole purpose of reference for the use of the products herein and Sanken can assume no responsibility for any infringement of industrial property rights, intellectual property rights or any other rights of Sanken or any third party which may result from its use. Although Sanken undertakes to enhance the quality and reliability of its products, the occurrence of failure and defect of semiconductor products at a certain rate is inevitable. Users of Sanken products are requested to take, at their own risk, preventative measures including safety design of the equipment or systems against any possible injury, death, fires or damages to the society due to device failure or malfunction. Sanken products listed in this document are designed and intended for the use as components in general purpose electronic equipment or apparatus (home appliances, office equipment, telecommunication equipment, measuring equipment, etc.). When considering the use of Sanken products in the applications where higher reliability is required (transportation equipment and its control systems, traffic signal control systems or equipment, fire/crime alarm systems, various safety devices, etc.), and whenever long life expectancy is required even in general purpose electronic equipment or apparatus, please contact your nearest Sanken sales representative to discuss, prior to the use of the products herein. The use of Sanken products without the written consent of Sanken in the applications where extremely high reliability is required (aerospace equipment, nuclear power control systems, life support systems, etc.) is strictly prohibited. In the case that you use Sanken semiconductor products or design your products by using Sanken semiconductor products, the reliability largely depends on the degree of derating to be made to the rated values. Derating may be interpreted as a case that an operation range is set by derating the load from each rated value or surge voltage or noise is considered for derating in order to assure or improve the reliability. In general, derating factors include electric stresses such as electric voltage, electric current, electric power etc., environmental stresses such as ambient temperature, humidity etc. and thermal stress caused due to self-heating of semiconductor products. For these stresses, instantaneous values, maximum values and minimum values must be taken into consideration. In addition, it should be noted that since power devices or IC’s including power devices have large self-heating value, the degree of derating of junction temperature affects the reliability significantly. When using the products specified herein by either (i) combining other products or materials therewith or (ii) physically, chemically or otherwise processing or treating the products, please duly consider all possible risks that may result from all such uses in advance and proceed therewith at your own responsibility. Anti radioactive ray design is not considered for the products listed herein. Sanken assumes no responsibility for any troubles, such as dropping products caused during transportation out of Sanken’s distribution network. The contents in this document must not be transcribed or copied without Sanken’s written consent. Copy Right: SANKEN ELECTRIC CO., LTD. Page.28