National Semiconductor LM3424 Скачать руководство пользователя страница 40 | Manualshive

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DESIGN #5 - BUCK-BOOST Application

300857h9

Features

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Input: 10V to 70V

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Output: 6 LEDs at 500mA

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PWM Dimming up to 10 kHz

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5 sec Fade-up

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MosFET R

DS-ON

Sensing

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700 kHz Switching Frequency

www.national.com

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LM3424

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Содержание LM3424

Страница 1: ...artup regulator that operates over a wide input range of 4 5V to 75V The internal PWM controller is designed for adjustable switching frequen cies of up to 2 0 MHz and external synchronization is possible The controller is capable of high speed PWM dimming and analog dimming Additional features include slope compen sation softstart over voltage and under voltage lock out cy cle by cycle current li...

Страница 2: ...sistor to GND to set the foldback slope 9 TSENSE Temp Sense Input Connect a resistor thermistor divider from VS to sense the temperature as explained in the Thermal Foldback Analog Dimming section 10 TREF Temp Foldback Reference Connect a resistor divider from VS to set the foldback reference voltage 11 VS Voltage Reference 2 45V reference for temperature foldback circuit and other external circui...

Страница 3: ...imum limits are guaranteed through test design or statistical correlation Typical values represent the most likely parametric norm at TJ 25 C and are provided for reference purposes only Unless otherwise stated the following condition applies VIN 14V Symbol Parameter Conditions Min Note 7 Typ Note 8 Max Note 7 Units STARTUP REGULATOR VCC VCC REG VCC Regulation ICC 0 mA 6 30 6 90 7 35 V ICC LIM VCC...

Страница 4: ...ote 9 500 kHz GATE DRIVER GATE RSRC GATE GATE Sourcing Resistance GATE High 2 0 6 0 Ω RSNK GATE GATE Sinking Resistance GATE Low 1 3 4 5 UNDER VOLTAGE LOCKOUT and DIM INPUT nDIM VTH nDIM nDIM UVLO Threshold 1 185 1 240 1 285 V IHYS nDIM nDIM Hysteresis Current 13 20 27 µA DIM DRIVER DDRV RSRC DDRV DDRV Sourcing Resistance DDRV High 13 5 30 0 Ω RSNK DDRV DDRV Sinking Resistance DDRV Low 3 5 10 0 nD...

Страница 5: ...ve to be derated Maximum ambient temperature TA MAX is dependent on the maximum operating junction temperature TJ MAX OP 125 C the maximum power dissipation of the device in the application PD MAX and the junction to ambient thermal resistance of the package in the application θJA as given by the following equation TA MAX TJ MAX OP θJA PD MAX In most applications there is little need for the full ...

Страница 6: ...857b6 Buck Boost Efficiency vs Input Voltage VO 21V 6 LEDs Note 10 300857b5 Boost LED Current vs Input Voltage VO 32V 9 LEDs Note 11 300857b8 Buck Boost LED Current vs Input Voltage VO 21V 6 LEDs Note 10 300857b7 Analog Dimming VO 21V 6 LEDs VIN 24V Note 10 300857b9 PWM Dimming VO 32V 9 LEDs VIN 24V Note 11 300857c0 www national com 6 LM3424 ...

Страница 7: ...ure 300857b0 VCC vs Junction Temperature 300857b1 VS vs Junction Temperature 300857b2 VLIM vs Junction Temperature 300857b3 tON MIN vs Junction Temperature 300857b4 fSW vs Junction Temperature 30085701 7 www national com LM3424 ...

Страница 8: ...SENSE 0 5V VTREF 1 5V 30085702 fSW vs RT 30085705 Ideal Thermal Foldback Varied Slope RREF1 RREF2 49 9 kΩ RNTC BK RBIAS 43 2 kΩ 300857k4 Ideal Thermal Foldback Varied Breakpoint RREF1 RREF2 49 9 kΩ RGAIN 10 kΩ 300857k5 www national com 8 LM3424 ...

Страница 9: ...djustable current sense threshold provides the capability to amplitude analog dim the LED current and the thermal fold back circuitry allows for precise temperature management of the LEDs Tthe output enable disable function coupled with an internal dimming drive circuit provides high speed PWM dimming through the use of an external MosFET placed at the LED load When designing the maximum attainabl...

Страница 10: ...sion ratio Buck Boost Buck boost PEAK CURRENT MODE CONTROL Peak current mode control is used by the LM3424 to regulate the average LED current through an array of HBLEDs This method of control uses a series resistor in the LED path to sense LED current and can use either a series resistor in the MosFET path or the MosFET RDS ON for both cycle by cycle current limit and input voltage feed forward T...

Страница 11: ...te the CSH pin to 1 24V and assuming ITF 0A ICSH can be calculated This means VSNS will be regulated as follows ILED can then be calculated The selection of the three resistors RSNS RCSH and RHSP is not arbitrary For matching and noise performance the sug gested signal current ICSH is approximately 100 µA This current does not flow in the LEDs and will not affect either the off state LED current o...

Страница 12: ...ure The nominal resistance of an NTC is the resistance when the temperature is 25 C R25 and in many datasheets this will be given a multiplier of 1 Then the resistance at a higher temperature will have a multiplier less than 1 i e R85 multiplier is 0 161 therefore R85 0 161 x R25 Given a de sired TBK and TEND the corresponding resistances at those temperatures RNTC BK and RNTC END can be found Usi...

Страница 13: ...cuit As the LED current is reduced the output voltage and the duty cycle decreases Eventually the mini mum on time is reached The lower the switching frequency the wider the linear dimming range Figure 6 shows how both CSH methods are physically implemented Method 1 uses an external potentiometer in the CSH path which is a simple addition to the existing circuitry However the LEDs cannot dim compl...

Страница 14: ...ition called current mode instability or sub harmonic oscillation can re sult if there is a perturbation of the MosFET current sense voltage at the IS pin due to noise or a some type of transient Through a mathematical geometrical analysis of the inductor current IL and the corresponding control current IC it can be shown that if D 0 5 the effect of the perturbation will decrease each switching cy...

Страница 15: ... for compensation of all topologies The uncompensated loop gain for a buck boost regulator is given by the following equation Where the uncompensated DC loop gain of the system is de scribed as And the output pole ωP1 is approximated And the right half plane zero ωZ1 is 300857a7 FIGURE 9 Uncompensated Loop Gain Frequency Response Figure 9 shows the uncompensated loop gain in a worst case scenario ...

Страница 16: ...compensation pole is placed low enough ensuring stability 300857a4 FIGURE 11 Compensated Loop Gain Frequency Response 30085761 FIGURE 12 Start up Waveforms START UP REGULATOR and SOFT START The LM3424 includes a high voltage low dropout bias regu lator When power is applied the regulator is enabled and sources current into an external capacitor CBYP connected to the VCC pin The recommended bypass ...

Страница 17: ...d Floating In the ground referenced configuration the voltage across ROV2 is VO 1 24V whereas in the floating configuration it is VO 620 mV where 620 mV approximates VBE of the PNP The over voltage hysteresis VHYSO is defined 30085759 FIGURE 14 Floating Output OVP Circuitry INPUT UNDER VOLTAGE LOCKOUT UVLO The nDIM pin is a dual function input that features an accurate 1 24V threshold with program...

Страница 18: ...ground referenced FET However with buck boost and buck topologies level shifting circuitry is nec essary to translate the PWM dim signal to the floating dimFET as shown in Figure 17 and Figure 18 When using a series dimFET to PWM dim the LED current more output capacitance is always better A general rule of thumb is to use a minimum of 40 µF when PWM dimming For most applications this will provide...

Страница 19: ...ting point as shown in Figure 19 For any application with more than 2 series LEDs RSNS can be neglected allowing rD to be approximated as the num ber of LEDs multiplied by rLED OUTPUT CAPACITOR For boost and buck boost regulators the output capacitor CO provides energy to the load when the recirculating diode D1 is reverse biased during the first switching subinterval An output capacitor in a buck...

Страница 20: ... is ac complished by checking the typical diode forward voltage from the I V curve on the product datasheet and multiplying by the average diode current In general higher current diodes have a lower forward voltage and come in better per forming packages minimizing both power losses and temper ature rise CIRCUIT LAYOUT The performance of any switching regulator depends as much upon the layout of t...

Страница 21: ...Basic Topology Schematics BOOST REGULATOR VIN VO 30085722 21 www national com LM3424 ...

Страница 22: ...BUCK REGULATOR VIN VO 30085751 www national com 22 LM3424 ...

Страница 23: ...BUCK BOOST REGULATOR 30085750 23 www national com LM3424 ...

Страница 24: ...equency fSW by solving for RT 3 AVERAGE LED CURRENT For all topologies set the average LED current ILED knowing the desired current sense voltage VSNS and solving for RSNS If the calculated RSNS is too far from a desired standard value then VSNS will have to be adjusted to obtain a standard value Setup the suggested signal current of 100 µA by assuming RCSH 12 4 kΩ and solving for RHSP If the calc...

Страница 25: ...t and Buck boost 7 PEAK CURRENT LIMIT Set the peak current limit ILIM by solving for the transistor path sense resistor RLIM 8 SLOPE COMPENSATION For all topologies the preferred method to set slope compen sation is to ensure any duty cycle is attainable for the nominal VO and chosen L by solving for RSLP 9 LOOP COMPENSATION Using a simple first order peak current mode control model neglecting any...

Страница 26: ...to attenuate switching noise and provide better gain margin As suming RFS 10Ω CFS is calculated according to the higher value of the pole and the RHP zero of the system shown as a maximizing function The total system loop gain T can then be written as Buck Boost and Buck boost 10 INPUT CAPACITANCE Set the nominal input voltage ripple ΔvIN PP by solving for the required capacitance CIN Buck Boost B...

Страница 27: ...e VFD solve for the nominal power dissipation PD 13 OUTPUT OVLO For boost and buck boost regulators output OVLO is pro grammed with the turn off threshold voltage VTURN OFF and the desired hysteresis VHYSO To set VHYSO solve for ROV2 To set VTURN OFF solve for ROV1 Boost Buck boost A small filter capacitor COVP 47 nF should be added from the OVP pin to ground to reduce coupled switching noise 14 I...

Страница 28: ... diode The DDRV pin should be connected to the gate of the dimFET with or without level shifting circuitry as described in the PWM Dimming section The dimFET should be rated to handle the average LED current and the nominal output voltage 17 ANALOG DIMMING METHOD Analog dimming can be performed several ways Method 1 Place a potentiometer in place of the thermistor in the thermal foldback circuit s...

Страница 29: ...PECIFICATIONS N 6 VLED 3 5V rLED 325 mΩ VIN 24V VIN MIN 10V VIN MAX 70V fSW 500 kHz VSNS 100 mV ILED 1A ΔiL PP 700 mA ΔiLED PP 12 mA ΔvIN PP 100 mV ILIM 6A VTURN ON 10V VHYS 3V VTURN OFF 40V VHYSO 10V TBK 70 C TEND 120 C tTSU 30 ms 29 www national com LM3424 ...

Страница 30: ...RHSP is actually 1 kΩ therefore ILED is The chosen components from step 3 are 4 THERMAL FOLDBACK Find the resistances corresponding to TBK and TEND RNTC BK 24 3 kΩ and RNTC END 7 15 kΩ from the manufacturer s datasheet Assuming RREF1 RREF2 49 9 kΩ then RBIAS RNTC BK 24 3 kΩ Solve for RGAIN The chosen components from step 4 are 5 INDUCTOR RIPPLE CURRENT Solve for L1 The closest standard inductor is...

Страница 31: ...t standard resistor is 0 04 Ω therefore ILIM is The chosen component from step 7 is 8 SLOPE COMPENSATION Solve for RSLP The chosen component from step 8 is 9 LOOP COMPENSATION ωP1 is approximated ωZ1 is approximated TU0 is approximated To ensure stability calculate ωP2 Solve for CCMP To attenuate switching noise calculate ωP3 Assume RFS 10Ω and solve for CFS The chosen components from step 9 are 3...

Страница 32: ...o the low RDS ON 50 mΩ Determine IT RMS and PT The chosen component from step 11 is 12 DIODE Determine minimum D1 voltage rating and current rating A 100V diode is chosen with a current rating of 12A and VD 600 mV Determine PD The chosen component from step 12 is 13 INPUT UVLO Solve for RUV2 The closest standard resistor is 150 kΩ therefore VHYS is Solve for RUV1 The closest standard resistor is 2...

Страница 33: ...y 100V 12A VISHAY 12CWQ10FNPBF 1 L1 33 µH 20 6 3A COILCRAFT MSS1278 333MLB 1 Q1 NMOS 100V 32A FAIRCHILD FDD3682 1 Q2 PNP 150V 600 mA FAIRCHILD MMBT5401 1 RBIAS 24 3 kΩ 1 VISHAY CRCW080524K3FKEA 1 RCSH 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 10Ω 1 VISHAY CRCW080510R0FKEA 1 RGAIN 6 81 kΩ 1 VISHAY CRCW08056K81FKEA 2 RHSP RHSN 1 0 kΩ 1 VISHAY CRCW08051K00FKEA 1 RLIM 0 04Ω 1 1W VISHAY WSL2512R0400FEA 1...

Страница 34: ...performed In all designs an RC filter 0 1 µF 10Ω is recommended at VIN placed as close as possible to the LM3424 device This filter is not shown in the following designs DESIGN 2 BOOST Application 300857h5 Features Input 8V to 28V Output 9 LEDs at 1A 65 C 100 C Thermal Foldback PWM Dimming up to 30kHz 700 kHz Switching Frequency www national com 34 LM3424 ...

Страница 35: ...3A COILCRAFT MSS1278 333MLB 2 Q1 Q2 NMOS 60V 8A VISHAY SI4436DY 1 Q3 NMOS 60V 115mA ON SEMI 2N7002ET1G 1 RBIAS 19 6 kΩ 1 VISHAY CRCW080519K6FKEA 2 RCSH ROV1 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 0Ω 1 VISHAY CRCW08050000Z0EA 1 RGAIN 6 49 kΩ 1 VISHAY CRCW08056K49FKEA 2 RHSP RHSN 1 0 kΩ 1 VISHAY CRCW08051K00FKEA 1 RLIM 0 06Ω 1 1W VISHAY WSL2512R0600FEA 1 ROV2 499 kΩ 1 VISHAY CRCW0805499KFKEA 2 RREF...

Страница 36: ...DESIGN 3 BUCK BOOST Application 300857h6 Features Input 10V to 30V Output 4 LEDs at 2A PWM Dimming up to 10kHz Analog Dimming 600 kHz Switching Frequency www national com 36 LM3424 ...

Страница 37: ...NMOS 60V 260mA ON SEMI 2N7002ET1G 1 Q4 PNP 40V 200 mA FAIRCHILD MMBT5087 1 Q5 PNP 150V 600 mA FAIRCHILD MMBT5401 1 Q6 NPN 300V 600 mA FAIRCHILD MMBTA42 1 Q7 NPN 40V 200 mA FAIRCHILD MMBT6428 3 RBIAS RREF1 RREF2 49 9 kΩ 1 VISHAY CRCW080549K9FKEA 2 RCSH RT 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RF 10Ω 1 VISHAY CRCW080510R0FKEA 1 RFS 0Ω 1 VISHAY CRCW08050000Z0EA 2 RGAIN RUV2 10 0 kΩ 1 VISHAY CRCW080510K...

Страница 38: ...DESIGN 4 BOOST Application 300857h7 Features Input 18V to 38V Output 12 LEDs at 700mA 85 C 125 C Thermal Foldback Analog Dimming 700 kHz Switching Frequency www national com 38 LM3424 ...

Страница 39: ...Y 1 Q2 NPN 40V 200 mA FAIRCHILD MMBT3904 1 Q3 Q4 dual pack Dual PNP 40V 200mA FAIRCHILD FFB3906 1 RADJ 100 kΩ potentiometer BOURNS 3352P 1 104 1 RBIAS 9 76 kΩ 1 VISHAY CRCW08059K76FKEA 1 RBIAS2 17 4 kΩ 1 VISHAY CRCW080517K4FKEA 3 RCSH ROV1 RUV1 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 10Ω 1 VISHAY CRCW080510R0FKEA 1 RGAIN 6 55 kΩ 1 VISHAY CRCW08056K55FKEA 3 RHSP RHSN RMAX 1 0 kΩ 1 VISHAY CRCW08051K...

Страница 40: ...SIGN 5 BUCK BOOST Application 300857h9 Features Input 10V to 70V Output 6 LEDs at 500mA PWM Dimming up to 10 kHz 5 sec Fade up MosFET RDS ON Sensing 700 kHz Switching Frequency www national com 40 LM3424 ...

Страница 41: ... L1 68 µH 20 4 3A COILCRAFT MSS1278 683MLB 2 Q1 Q2 NMOS 100V 32A FAIRCHILD FDD3682 1 Q3 NMOS 60V 260mA ON SEMI 2N7002ET1G 1 Q4 PNP 40V 200mA FAIRCHILD MMBT5087 1 Q5 PNP 150V 600 mA FAIRCHILD MMBT5401 1 Q6 NPN 300V 600mA FAIRCHILD MMBTA42 1 Q7 NPN 40V 200mA FAIRCHILD MMBT6428 3 RBIAS RREF1 RREF2 49 9 kΩ 1 VISHAY CRCW080549K9FKEA 1 RCSH 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 0Ω 1 VISHAY CRCW0805000...

Страница 42: ...DESIGN 6 BUCK Application 300857h8 Features Input 15V to 50V Output 3 LEDS AT 1 25A PWM Dimming up to 50 kHz Analog Dimming 700 kHz Switching Frequency www national com 42 LM3424 ...

Страница 43: ...FT MSS1278 223MLB 1 Q1 NMOS 60V 8A VISHAY SI4436DY 1 Q2 PMOS 30V 6 2A VISHAY SI3483DV 1 Q3 NMOS 60V 115mA ON SEMI 2N7002ET1G 1 Q4 PNP 150V 600 mA FAIRCHILD MMBT5401 3 RBIAS RREF1 RREF2 49 9 kΩ 1 VISHAY CRCW080549K9FKEA 1 RCSH 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 0Ω 1 VISHAY CRCW08050000OZEA 1 RGAIN RT 10 0 kΩ 1 VISHAY CRCW080510K0FKEA 2 RHSP RHSN 1 0 kΩ 1 VISHAY CRCW08051K00FKEA 1 RLIM 0 04Ω 1 ...

Страница 44: ...ESIGN 7 BUCK BOOST Application 300857i0 Features Input 15V to 60V Output 8 LEDs at 2 5A 80 C 110 C Thermal Foldback 500 kHz Switching Frequency External Synchronization 500 kHz www national com 44 LM3424 ...

Страница 45: ...WQ10FNPBF 1 L1 22 µH 20 7 2A COILCRAFT MSS1278 223MLB 1 Q1 NMOS 100V 32A FAIRCHILD FDD3682 1 Q2 PNP 150V 600 mA FAIRCHILD MMBT5401 1 RBIAS 11 5 kΩ 1 VISHAY CRCW080511K5FKEA 2 RCSH ROV1 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 10Ω 1 VISHAY CRCW080510R0FKEA 1 RGAIN 5 49 kΩ 1 VISHAY CRCW08055K49FKEA 2 RHSP RHSN 1 0 kΩ 1 VISHAY CRCW08051K00FKEA 2 RLIM RSNS 0 04Ω 1 1W VISHAY WSL2512R0400FEA 1 ROV1 15 8 ...

Страница 46: ...DESIGN 8 SEPIC Application 300857i8 Features Input 9V to 36V Output 5 LEDs at 750mA 60 C 120 C Thermal Foldback PWM Dimming up to 30 kHz 500 kHz Switching Frequency www national com 46 LM3424 ...

Страница 47: ...NMOS 60V 8A VISHAY SI4436DY 1 Q3 NMOS 60V 115 mA ON SEMI 2N7002ET1G 1 RBIAS 23 7 kΩ 1 VISHAY CRCW080523K7FKEA 1 RCSH 12 4 kΩ 1 VISHAY CRCW080512K4FKEA 1 RFS 0Ω 1 VISHAY CRCW08050000OZEA 1 RGAIN 9 31 kΩ 1 VISHAY CRCW08059K31FKEA 2 RHSP RHSN 750Ω 1 VISHAY CRCW0805750RFKEA 1 RLIM 0 04Ω 1 1W VISHAY WSL2512R0400FEA 1 ROV1 15 8 kΩ 1 VISHAY CRCW080515K8FKEA 1 ROV2 499 kΩ 1 VISHAY CRCW0805499KFKEA 2 RREF1...

Страница 48: ...Physical Dimensions inches millimeters unless otherwise noted TSSOP 20 Pin EP Package MXA For Ordering Refer to Ordering Information Table NS Package Number MXA20A www national com 48 LM3424 ...

Страница 49: ...Notes 49 www national com LM3424 ...

Страница 50: ...PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS BUYERS SHOULD PROVIDE ADEQUATE DESIGN TESTING AND OPERATING SAFEGUARDS EXCEPT AS PROVIDED IN NATIONA...

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