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Table Of Contents

This is information on a product in full production.

January 2013 Doc ID 023951 Rev 1 1/51

LED5000

3 A monolithic step-down current source with dimming capability

Datasheet − production data

Features

■ 5.5 V to 48 V operating input voltage range

■ 850 kHz fixed switching frequency

■ 200 mV typ. current sense voltage drop

■ buck / buck-boost / floating boost topologies

■ PWM dimming

■ ±3% output current accuracy over temperature

■ 200 mW typical RDS

■

Peak current mode architecture

■ Short-circuit protection

■ Compliant with ceramic output capacitors

■ Inhibit for zero current consumption

■ Thermal shutdown

Applications

■ High brightness LED driving

■ Street lighting

■ Signage

■ Halogen bulb replacement

■ General lighting

Description

The LED5000 is an 850 kHz fixed switching

frequency monolithic step-down DC-DC converter

designed to operate as a precise constant current

source with an adjustable current capability up to

3 A DC. The embedded PWM dimming circuitry

features LED brightness control. The regulated

output current level is set by connecting a sensing

resistor to the feedback pin. The 200 mV typical

SENSE

voltage drop enhances performance in

terms of efficiency. The size of the overall

application is minimized thanks to the high

switching frequency and its compatibility with

ceramic output capacitors. The device is fully

protected against overheating, overcurrent and

output short-circuit. The LED5000 is available in

an HSOP8 package.

Figure 1. Typical application circuit

HPSO8

CIN CFLT

VIN

GND

1 2

DIM

RS COUT

U1LED5000

BOOT

DIM

INH

COMP

GND

VIN

AM13485v1

www.st.com

Summary of content (51 pages)

PAGE 1
LED5000 3 A monolithic step-down current source with dimming capability Datasheet − production data Features ■ 5.5 V to 48 V operating input voltage range ■ 850 kHz fixed switching frequency ■ 200 mV typ.
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Contents LED5000 Contents 1 2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Maximum ratings . . . . .
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LED5000 6 Contents 5.9.2 Inductor and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.9.3 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.10 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.11 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.12 Short-circuit protection . . . . . . . . . . . .
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List of tables LED5000 List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. 4/51 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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LED5000 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Pin settings LED5000 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) HSOP8 1.2 Pin description Table 1. 6/51 AM13486v1 Pin description Type Description 1 BOOT Analog circuitry power supply connection 2 DIM Dimming control input. Logic low prevents the switching activity, logic high enables it. A square wave on this pin implements LEDs current PWM dimming. Connect to VIN if not used (see Chapter 5.8) 3 INH Inhibit pin. Connect to GND if not used.
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LED5000 Maximum ratings 2 Maximum ratings 2.1 Maximum ratings Table 2. Absolute maximum ratings Symbol Unit Power supply input voltage -0.3 to 52 V VINH Inhibit input -0.3 to 7 V VDIM Dimming input -0.3 to (VIN+0.3) V VCOMP Comp output -0.3 to 3 V BOOT Bootstrap pin -0.3 to 55 V -1 to (VIN+0.3) V -0.3 to 3 V Operating junction temperature range -40 to 150 °C TSTG Storage temperature range -65 to 150 °C TLEAD Lead temperature (soldering 10 sec.
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Electrical characteristics 3 LED5000 Electrical characteristics All tests performed at TJ = 25 °C, VCC = 12 V, VINH =0 V unless otherwise specified. The specification is guaranteed from (-40 to +125) TJ temperature range by design, characterization and statistical correlation. Table 5. Symbol VIN RDS(on) ISW Electrical characteristics Parameter Test condition Min Operating input voltage range MOSFET on resistance Max Unit 48 V 0.2 0.4 Ω 4.5 5.2 A 5.5 ISW=1 A Maximum limiting current 3.
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LED5000 Electrical characteristics Table 5. Electrical characteristics (continued) Symbol Parameter Test condition Min Typ Max Unit Dimming Switching activity VIN=5.5 V to 48 V VDIM Dimming levels 2.2 V Switching activity prevented VIN=5.5 V to 48 V 0.5 V Error amplifier VOH High level output voltage VFB = 0 V VOL Low level output voltage VFB = 400 mV Source output current VCOMP = 1.5 V; VFB = 0 V 16 Io sink Sink output current VCOMP = 1.5 V; VFB = 0.
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Functional description 4 LED5000 Functional description The LED5000 is based on a “peak current mode” architecture with fixed frequency control. As a consequence the intersection between the error amplifier output and the sensed inductor current generates the control signal to drive the power switch.
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LED5000 4.1 Functional description Power supply and voltage reference The internal regulator circuit consists of a startup circuit, an internal voltage pre-regulator, the bandgap voltage reference and the bias block that provides current to all the blocks. The starter supplies the startup current to the entire device when the input voltage goes high and the device is enabled (inhibit pin connected to ground).
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Functional description LED5000 During normal operation a new soft-start cycle takes place in case of: ● thermal shutdown event ● UVLO event The soft-start is disabled during the dimming operation to maximize the dimming performance. 4.4 Dimming block The DIM input features the LED brightness control with the PWM dimming operation (see Chapter 5.8). 4.5 Inhibit block The inhibit block features the standby mode accordingly with Table 5: Electrical characteristics.
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LED5000 Application notes - buck conversion 5 Application notes - buck conversion 5.1 Closing the loop Figure 6. Block diagram of the loop GCO(s) VIN PWM control Current sense HS switch L VOUT LC filter LS switch COUT error PWM + amplifier VCONTROL + comparator RC FB VREF RS compensation network CC α LED AO(s) AM13490v1 5.
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Application notes - buck conversion LED5000 Equation 2 1 ωZ = ---------------------------------ESR ⋅ C OUT Equation 3 m C ⋅ ( 1 – D ) – 0.
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LED5000 Application notes - buck conversion Figure 7. Transconductance embedded error amplifier + E/A COMP - FB RC CP CC V+ R0 dV C0 RC CP CC Gm dV AM13491v1 RC and CC introduce a pole and a zero in the open loop gain. CP does not significantly affect system stability but it can be useful to reduce the noise at the output of the error amplifier.
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Application notes - buck conversion 5.4 LED5000 LED small signal model Once the system reaches the working condition the LEDs composing the row are biased and their equivalent circuit can be considered as a resistor for frequencies << 1 MHz. The LED manufacturer typically provides the equivalent dynamic resistance of the LED biased at different DC current. This parameter is required to study the behavior of the system in the small signal analysis.
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LED5000 Application notes - buck conversion Figure 9. Load equivalent circuit L Dled1 VIN D COUT Dled2 Rs L Rd1 VIN D1 COUT Rd2 Rs AM13493v1 As a consequence the LED equivalent circuit gives the αLED(s) term correlating the output voltage with the high impedance FB input: Equation 13 R SENSE αLED ( n LED ) = -----------------------------------------------------------n LED ⋅ rLED + R SENSE 5.
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Application notes - buck conversion LED5000 With the power components selected in accordance with Chapter 5.9: Component selection and given the BW specification, the components composing the compensation network can be calculated as: Equation 16 RC R LOAD ⋅ TSW 1 + ------------------------------------ ⋅ [ m C ⋅ ( 1 – D ) – 0.
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LED5000 Application notes - buck conversion Equation 21 RC = 47 kΩ C C = 680 pF CC = 12 pF The gain and phase margin bode diagrams are plotted, respectively, in Figure 10 and Figure 11. Figure 10. Module plot External loop module 100 87 74 61 Module [dB] 48 35 22 9 4 17 30 0.1 1 10 3 1 .10 100 4 1 .10 5 1 .10 Frequency [Hz] 6 1 .10 AM13494v1 Figure 11. Phase plot External loop gain phase 180 157.5 135 112.5 90 67.5 45 22.5 0 0.1 1 10 100 3 1 .10 4 1 .10 5 1 .10 6 1 .
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Application notes - buck conversion LED5000 The cut-off frequency and the phase margin are: Equation 22 f C = 65 kHz 5.8 pm = 66° Dimming operation The dimming input disables the switching activity, masking the PWM comparator output. The inductor current dynamic performance when dimming input goes high depends on the designed system response. The best dimming performance is obtained by maximizing the bandwidth and phase margin, when possible.
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LED5000 Application notes - buck conversion Figure 13. LED rising edge operation AM13497v1 Figure 14.
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Application notes - buck conversion 5.8.1 LED5000 Dimming frequency vs. dimming depth As seen in Chapter 5.8 the LEDs current rising and falling edge time mainly depends on the system bandwidth (TRISE) and the selected output capacitor value (TRISE and TFALL). The dimming performance depends on the minimum current pulse shape specification of the final application.
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LED5000 Application notes - buck conversion the external power components and the compensation network are selected, a direct measurement to determine TRISE, TFALL (see Equation 24) is necessary to certify the achieved dimming performance. 5.9 Component selection 5.9.1 Sensing resistor In closed loop operation the LED5000 feedback pin voltage is 200 mV, so the sensing resistor calculation is expressed as: Equation 26 mVR S = 200 -------------------ILED Since the main loop (see Chapter 5.
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Application notes - buck conversion LED5000 The LED ripple current can be calculated as the inductor ripple current ratio flowing into the output impedance using the Laplace transform (see Figure 11): Equation 27 8 ----- ⋅ ΔIL ⋅ ( 1 + s ⋅ ESR ⋅ C OUT ) 2 π ΔIRIPPLE ( s ) = ------------------------------------------------------------------------------------------------------------------1 + s ⋅ ( R S + ESR + n LED ⋅ RLED ) ⋅ C OUT where the term 8/π2 represents the main harmonic of the inductor current rip
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LED5000 Application notes - buck conversion Equation 32 ΔIL ---------- = 0.5 I LED which is satisfied selecting a10 μH inductor value. The output capacitor value has to be dimensioned according to Equation 31 Finally, given the selected inductor value, a 1 μF ceramic capacitor value keeps the LED current ripple ratio lower than the 2% of the nominal current. An output ceramic capacitor type (negligible ESR) is suggested to minimize the ripple contribution given a fixed capacitor value. Table 7.
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Application notes - buck conversion LED5000 Equation 35 VOUT + V F D MIN = ------------------------------------V INMAX – V SW Where VF is the free wheeling diode forward voltage and VSW the voltage drop across the internal PDMOS. Considering the range DMIN to DMAX, it is possible to determine the max IRMS going through the input capacitor.
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LED5000 Application notes - buck conversion The input and output loops are minimized to avoid radiation and high frequency resonance problems. The feedback pin to the sensing resistor path must be designed as short as possible to avoid pick-up noise. Another important issue is the ground plane of the board.
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Application notes - buck conversion LED5000 higher than this value to compensate for the losses in the overall application. For this reason, the conduction losses related to the RDSON increase compared to an ideal case. ● Switching losses due to turning ON and OFF.
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LED5000 Application notes - buck conversion For the calculation we can estimate RDSON_HS = 300 mΩ as a consequence of Tj increase during the operation. TSW_EQ is approximately 12 ns. IQ has a typical value of 2.4 mA at VIN = 48 V. The overall internal losses are: Equation 41 2 PTOT = R DSON_HS ⋅ ( I OUT ) ⋅ D + V IN ⋅ IOUT ⋅ f SW ⋅ TSW + V IN ⋅ IQ Equation 42 2 P TOT = 0.3 ⋅ 1.5 ⋅ 0.7 + 42 ⋅ 1.5 ⋅ 12 ⋅ 10 –9 3 ⋅ 850 ⋅ 10 + 42 ⋅ 2.4 ⋅ 10 –3 ≅ 1.
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Application notes - buck conversion LED5000 Equation 45 – ( V OUT + DCR L ⋅ I + V FW DIODE ) ΔI L TON = ---------------------------------------------------------------------------------------- ( T OFF ) L where DCRL is the series resistance of the inductor and VFWDIODE is the forward voltage drop across the external rectifying diode.
PAGE 31
LED5000 Application notes - buck conversion Figure 19. constant current protection triggering hiccup mode AM13503v1 Application circuit Figure 20. Evaluation board application circuit C6 100nF U1 TP1 2 TP2 7 3 R1 INH 10k BOOT TP4 47uH 8 VLED+ D3 DIM BZX384-C39 C8 NM VIN INH GND EP FB COMP 5 VLEDR4 47k TP5 TP8 6 R2 C1 10uF 50V GND SW C2 10uF 50V C3 100nF 50V JP2 NM EP D2 4 R3 24.9K 1 D1 VIN 1 RS R56 2 STPS3L60U DIM LED5000 L1 JP1 BZX384-4V7 5.
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Application notes - buck conversion LED5000 Equation 49 V OUT = V FB + V ZENER_DIODE V FB IZENER_DIODE = -------------------RS + R1 R1 must be dimensioned to limit the D1 rated power so it is an inexpensive small signal Zener diode. The overvoltage limits the output voltage in case of LED disconnection so protecting LEDs when the string is reconnected with the device enabled.
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LED5000 Application notes - buck conversion Figure 21. PCB layout (component side) AM13505v1 Figure 22.
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Application notes - alternative topologies 6 LED5000 Application notes - alternative topologies Thanks to the wide input voltage range, the adjustable external compensation network and enhanced dimming capability, the LED5000 is suitable to implement boost and buck-boost topologies. 6.1 Inverting buck-boost The buck-boost topology fits the application with an input voltage range that overlaps the output voltage, which is the voltage drop across the LEDs and the sensing resistor.
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LED5000 Application notes - alternative topologies Since the maximum operating voltage of the LED5000 is 48 V, according to Equation 51 the maximum input voltage of the application is 48-18.7=29.
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Application notes - alternative topologies LED5000 Figure 24. LED current source based on inverting BB topology C1 100nF 3 7 Q1 BC807-16 TP3 DIM C2 10uF 50V 3 C3 10uF 50V R2 100K C5 1uF 50V R3 10K 8 DIM VIN FB R1 5 100K VLEDTP2 INH GND EP C4 100nF 50V 6 R4 EP COMP 4 R5 10K 47K C7 C6 15pF 1.5nF TP4 GND D1 RS1 STPS3L60U JUMPER TP1 VIN SW BZX384-C39 2 LED5000 BOOT L1 1 XAL6060-15uH 1 U1 T1 2 D2 0.2 small signal -Vout C9 NM C8 4.
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LED5000 Application notes - alternative topologies Equation 57 V OUT = V FB + V ZENER_DIODE V FB IZENER_DIODE = -------------------RS + R1 R1 must be dimensioned to limit the D1 rated power so it is an inexpensive small signal Zener diode. The overvoltage protection plays an important role for the inverting buck-boost topology. In fact, in case of open row, the output voltage tends to diverge thus exceeding the input voltage absolute maximum rate and the device would be damaged (see Equation 50).
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Application notes - alternative topologies 6.2 LED5000 Positive buck-boost Positive buck-boost fits those applications that require a buck-boost topology (i.e. the input voltage range crosses the output voltage value) and where the inverting buck-boost is not suitable because of the main constraints for the final application (refer to Chapter 6.1).
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LED5000 Application notes - alternative topologies Equation 61 ILOAD I SW = -------------------------1 – D REAL This is due to the fact that the current flowing through the internal power switch is delivered to the output only during the OFF phase. The switch peak current must be lower than the minimum current limit of the overcurrent protection (see Section Table 5.: Electrical characteristics for details) while the average current must be lower than the rated DC current of the device.
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Application notes - alternative topologies LED5000 In case of open row, the positive output voltage tends to diverge, exceeding the D3 maximum reverse voltage and so the diode would be damaged. The overvoltage protection limits VOUT and it protects the power components in case of load disconnection. The network D4, R8 implements a level shifter to drive the gate of the transistor Q1.
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LED5000 Application notes - alternative topologies Equation 66 VIN_START = V OP_MIN + V DIODE = 5.5V + V DIODE where VOP_MIN is the minimum operating voltage. The equations for the floating boost are: Equation 67 V IN V OUT = ---------------------------1 – D IDEAL The ideal duty cycle DIDEAL for the boost converter is: Equation 68 V OUT – VIN D IDEAL = ---------------------------V OUT As seen for the buck-boost topologies (Chapter 6.1 and Chapter 6.
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Application notes - alternative topologies LED5000 Figure 31 shows the circuit schematic for an LED current source based on the floating boost topology. The input voltage ranges from 12 to 36 V and it can drive a string composed of 11 LEDs with 0.7 A DC (VFW_LED = 3.74 V so VOUT=41 V). Figure 31.
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LED5000 Application notes - alternative topologies Figure 32. Floating BB dimming operation AM13516v1 To design the compensation network for the boost topology please refer to paragraph Chapter 6.4: Compensation network design for alternative topologies. Figure 33. Floating boost PCB layout (component side) AM13517v1 Figure 34.
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Application notes - alternative topologies 6.
PAGE 45
LED5000 Application notes - alternative topologies Equation 78 KD ωp 1 f p = ------------ = ------------- ⋅ --------------------------------2 ⋅ π C O ⋅ R LOAD 2⋅ π Table 10.
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Application notes - alternative topologies LED5000 Equation 80 K C C = --------------------------------------------2 ⋅ π ⋅ R C ⋅ BW where K represents the leading position of the FZ (Equation 11) in respect to the system bandwidth. In general a decade (K=10) gives enough phase margin to the overall small loop transfer function. 6.4.
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LED5000 7 Package mechanical data Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Table 11. HSOP8 mechanical data mm Dim. Min. Typ. Max. A 1.75 A1 0.15 A2 1.25 b 0.38 0.51 c 0.17 0.25 D 4.80 4.90 5.00 D1 3.10 3.30 3.
PAGE 48
Package mechanical data LED5000 Figure 35.
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LED5000 8 Ordering information Ordering information Table 12.
PAGE 50
Revision history 9 LED5000 Revision history Table 13. 50/51 Document revision history Date Revision 31-Jan-2013 1 Changes Initial release.
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LED5000 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale.