LED2000DR

LED2000 3 A monolithic step-down current source with synchronous rectification Datasheet - production data Applications • High brightness LED driving • Halogen bulb replacement • General lighting • Signage 62 9)4)31[ Description The LED2000 is an 850 kHz fixed switching frequency monolithic step-down DC-DC converter designed to operate as 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 is set connecting a sensing resistor to the feedback pin. The embedded synchronous rectification and the 100 mV typical RSENSE voltage drop enhance the efficiency performance. The size of the overall application is minimized thanks to the high switching frequency and ceramic output capacitor compatibility. The device is fully protected against thermal overheating, overcurrent and output short-circuit. The LED2000 is available in VFQFPN 4 mm x 4 mm 8-lead, and standard SO8 package. Features • 3.0 V to 18 V operating input voltage range • 850 kHz fixed switching frequency • 100 mV typ. current sense voltage drop • PWM dimming • ± 7% output current accuracy • Synchronous rectification • 95 mΩ HS / 69 mΩ LS typical RDS(on) • Peak current mode architecture • Embedded compensation network • Internal current limiting • Ceramic output capacitor compliant • Thermal shutdown Figure 1. Typical application circuit /(' 9,1 ',0 &,1  9,1B6:  9,1B$  ',0 &)/7 3*1' (3   6:  )% $*1'   / 56 &287 *1' $0Y September 2021 This is information on a product in full production. DocID023432 Rev 7 1/41 www.st.com Contents LED2000 Contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 5.1 Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.2 Voltage monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4 Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.5 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Application notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2 GCO(s) control to output transfer function . . . . . . . . . . . . . . . . . . . . . . . . 12 6.3 Error amplifier compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.4 LED small signal model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.5 Total loop gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.6 Dimming operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Dimming frequency vs. dimming depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.7 7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1 7.2 2/41 EDesign Suite software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1.1 Sensing resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1.2 Inductor and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1.3 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 DocID023432 Rev 7 LED2000 Contents 7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 10 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 DocID023432 Rev 7 3/41 41 List of tables LED2000 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. 4/41 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Uncompensated error amplifier characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 List of ceramic capacitors for the LED2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 VFQFPN8 (4 x 4 x 1.08 mm) mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 SO8 mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 DocID023432 Rev 7 LED2000 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. Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Pin connection (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 LED2000 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Internal circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Block diagram of the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Transconductance embedded error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Equivalent series resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Load equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Module plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Phase plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Dimming operation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 LED current falling edge operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Dimming signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 EDesign Suite screenshot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Equivalent circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Layout example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Switching losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Constant current protection triggering hiccup mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Demonstration board application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 PCB layout (component side) VFQFPN package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 PCB layout (bottom side) VFQFPN package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 PCB layout (component side) SO8 package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 PCB layout (bottom side) SO8 package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Dimming operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 LED current rising edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 LED current falling edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Hiccup current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Efficiency vs. IOUT (VIN 32 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Thermal shutdown protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 VFQFPN8 (4 x 4 x 1.08 mm) package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 SO8 package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 DocID023432 Rev 7 5/41 41 Pin settings LED2000 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) SW 1 8 PGND DIM VINSW GND AGND VINA NC DIM 4 FB SO8 - BW VFQFPN 1.2 5 AM12893v1 Pin description Table 1. Pin description Package/pin Type 6/41 VFQFPN S08-BW 1 3 Description VINA Analog circuitry power supply connection 2 4 DIM Dimming control input. Logic low prevents the switching activity, logic high enables it. A square wave on this pin implements LED current PWM dimming. Connect to VINA if not used (see Section 6.6) 3 5 FB Feedback input. Connect a proper sensing resistor to set the LED current 4 6 AGND 5 - NC 6 8 VINSW 7 1 SW 8 2 PGND - 7 GND Analog circuitry ground connection Not connected Power input voltage Regulator switching pin Power ground Connect to AGND DocID023432 Rev 7 LED2000 2 Maximum ratings Maximum ratings Table 2. Absolute maximum ratings Symbol VINSW 3 Parameter Value Power input voltage -0.3 to 20 VINA Input voltage -0.3 to 20 VDIM Dimming voltage VSW Output switching voltage VPG Power Good -0.3 to VIN VFB Feedback voltage -0.3 to 2.5 IFB FB current -0.3 to VINA -1 to VIN Unit V -1 to +1 mA 2 W PTOT Power dissipation at TA < 60 °C TOP Operating junction temperature range -40 to 150 °C Tstg Storage temperature range -55 to 150 °C Value Unit Thermal data Table 3. Thermal data Symbol RthJA Parameter Maximum thermal resistance junction-ambient(1) VFQFPN 40 SO8-BW 65 °C/W 1. Package mounted on demonstration board. DocID023432 Rev 7 7/41 41 Electrical characteristics 4 LED2000 Electrical characteristics TJ = 25 °C, VCC = 12 V, unless otherwise specified. Table 4. Electrical characteristics Value Symbol Parameter Test conditions Unit Min. Operating input voltage range VIN See(1) Typ. 3 Max. 18 Device ON level 2.6 2.75 2.9 Device OFF level 2.4 2.55 2.7 TJ = 25 °C 90 97 104 TJ = 125 °C 90 100 110 V VFB Feedback voltage IFB VFB pin bias current See(1) RDSON-P High-side switch on-resistance ISW = 750 mA 95 mΩ RDSON-N Low-side switch on-resistance ISW = 750 mA 69 mΩ Maximum limiting current See(2) 5 A ILIM 600 mV nA Oscillator FSW D Switching frequency 0.7 (2) Duty cycle See 0.85 0 1 MHz 100 % 2.5 mA DC characteristics IQ Quiescent current 1.5 Dimming Switching activity 1.2 VDIM DIM threshold voltage IDIM DIM current 2 µA Soft-start duration 1 ms Thermal shutdown 150 Hystereris 15 Switching activity prevented V 0.4 Soft-start TSS Protection TSHDN °C 1. Specifications referred to TJ from -40 to +125 °C. Specifications in the -40 to +125 °C temperature range are assured by design, characterization and statistical correlation. 2. Guaranteed by design. 8/41 DocID023432 Rev 7 LED2000 5 Functional description Functional description The LED2000 device 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. The main internal blocks shown in the block diagram in Figure 3 are: • High-side and low-side embedded power element for synchronous rectification • A fully integrated sawtooth oscillator with a typical frequency of 850 kHz • A transconductance error amplifier • A high-side current sense amplifier to track the inductor current • A pulse width modulator (PWM) comparator and the circuitry necessary to drive the internal power element • The soft-start circuitry to decrease the inrush current at power-up • The current limitation circuit based on the pulse-by-pulse current protection with frequency divider • The dimming circuitry for output current PWM • The thermal protection function circuitry. Figure 3. LED2000 block diagram VI N A V I N SW OCP REF OSC I2 V COMP I _ SENSE RSENSE REGULATOR UVLO Vdrv_p OCP MOSFET CONTROL LOGIC Vsum Vc PWM DRIVER Vdrv _n SW OTP DMD E/A DIMMING DRIVER SOFT-START 0.1V FB DIM GNDA GNDP AM12894v1 DocID023432 Rev 7 9/41 41 Functional description 5.1 LED2000 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. The pre-regulator block supplies the BandGap cell with a preregulated voltage that has a very low supply voltage noise sensitivity. 5.2 Voltage monitor An internal block continuously senses the VCC, Vref and Vbg. If the monitored voltages are good, the regulator begins operating. There is also a hysteresis on the VCC (UVLO). Figure 4. Internal circuit Vcc PREREGULATOR STARTER VREG BANDGAP IC BIAS D00IN126 5.3 VREF AM12895v1 Soft-start The startup phase is implemented ramping the reference of the embedded error amplifier in 1 ms typ. time. It minimizes the inrush current and decreases the stress of the power components at power-up. During normal operation a new soft-start cycle takes place in case of: • Thermal shutdown event • UVLO event. The soft-start is disabled when DIM input goes high in order to maximize the dimming performance. 5.4 Error amplifier The voltage error amplifier is the core of the loop regulation. It is a transconductance operational amplifier whose non-inverting input is connected to the internal voltage reference (100 mV), while the inverting input (FB) is connected to the output current sensing resistor. The error amplifier is internally compensated to minimize the size of the final application. 10/41 DocID023432 Rev 7 LED2000 Functional description Table 5. Uncompensated error amplifier characteristics Description Value Transconductance 250 µS Low frequency gain 96 dB CC 195 pF RC 70 KΩ The error amplifier output is compared with the inductor current sense information to perform PWM control. 5.5 Thermal shutdown The shutdown block generates a signal that disables the power stage if the temperature of the chip goes higher than a fixed internal threshold (150 ± 10 °C typical). The sensing element of the chip is close to the PDMOS area, ensuring fast and accurate temperature detection. A 15 °C typical hysteresis prevents the device from turning ON and OFF continuously during the protection operation. DocID023432 Rev 7 11/41 41 Application notes LED2000 6 Application notes 6.1 Closing the loop Figure 5. 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 A O(s) 6.2 GCO(s) control to output transfer function The accurate control to output transfer function for a buck peak current mode converter can be written as: Equation 1 s  1 + ----  ω R0 1 z G CO ( s ) = ------- ⋅ ---------------------------------------------------------------------------------------- ⋅ ---------------------- ⋅ FH ( s ) Ri R 0 ⋅ T SW s   1 + ----------------------- ⋅ [ m C ⋅ ( 1 – D ) – 0.5 ]  1 + -----ω p L where R0 represents the load resistance, Ri the equivalent sensing resistor of the current sense circuitry, ωp the single pole introduced by the LC filter and ωz the zero given by the ESR of the output capacitor. FH(s) accounts for the sampling effect performed by the PWM comparator on the output of the error amplifier that introduces a double pole at one half of the switching frequency. 12/41 DocID023432 Rev 7 LED2000 Application notes Equation 2 1 ω Z = ------------------------------ESR ⋅ C OUT Equation 3 m C ⋅ ( 1 – D ) – 0.5 1 ω P = -------------------------------------- + --------------------------------------------R LOAD ⋅ C OUT L ⋅ C OUT ⋅ fSW where: Equation 4 Se   m C = 1 + -----Sn  S = V ⋅ f pp SW  e  V IN – V OUT  S = ----------------------------- ⋅ Ri  n L Sn represents the slope of the sensed inductor current, Se the slope of the external ramp (VPP peak-to-peak amplitude) that implements the slope compensation to avoid subharmonic oscillations at duty cycle over 50%. The sampling effect contribution FH(s) is: Equation 5 1 FH ( s ) = -----------------------------------------2 s s 1 + ------------------- + ------2 ωn ⋅ QP ω n where: Equation 6 ω n = π ⋅ f SW and Equation 7 1 Q P = ---------------------------------------------------------π ⋅ [ m C ⋅ ( 1 – D ) – 0.5 ] 6.3 Error amplifier compensation network The LED2000 device embeds (see Figure 6) the error amplifier and a pre-defined compensation network which is effective in stabilizing the system in most application conditions. DocID023432 Rev 7 13/41 41 Application notes LED2000 Figure 6. Transconductance embedded error amplifier E/A + COMP - FB RC CP CC V+ R0 dV C0 Gm dV RC CP CC AM12897v1 RC and CC introduce a pole and a zero in the open loop gain. CP does not significantly affect system stability but it is useful to reduce the noise at the output of the error amplifier. The transfer function of the error amplifier and its compensation network is: Equation 8 A V0 ⋅ ( 1 + s ⋅ R c ⋅ C c ) A 0 ( s ) = ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------2 s ⋅ R0 ⋅ ( C0 + Cp ) ⋅ Rc ⋅ Cc + s ⋅ ( R0 ⋅ Cc + R0 ⋅ ( C0 + Cp ) + Rc ⋅ Cc ) + 1 where Avo = Gm · Ro. The poles of this transfer function are (if CC >> C0 + CP): Equation 9 1 fP LF = ---------------------------------2 ⋅ π ⋅ R0 ⋅ Cc Equation 10 1 f P HF = ---------------------------------------------------2 ⋅ π ⋅ Rc ⋅ ( C0 + Cp ) whereas the zero is defined as: Equation 11 1 F Z = --------------------------------2 ⋅ π ⋅ Rc ⋅ Cc 14/41 DocID023432 Rev 7 LED2000 Application notes The embedded compensation network is RC = 70 K, CC = 195 pF while CP and CO can be considered as negligible. The error amplifier output resistance is 240 MΩ, so the relevant singularities are: Equation 12 f Z = 11, 6 kHz 6.4 f P LF = 3, 4 Hz 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