LED2001 4 A monolithic step-down current source with synchronous rectification Datasheet - production data Applications • High brightness LED driving • Halogen bulb replacement • General lighting • Signage HSOP8 VFQFPN8 4x4 Description Features The LED2001 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 4 A DC.
Contents LED2001 Contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Thermal data . . . . . . .
LED2001 Contents 7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 8 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9 Ordering information . . . . . . . . . . . . . .
List of tables LED2001 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. 4/42 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LED2001 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin settings LED2001 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) VINA 1 9 8 PGND 9 DIM DIM 2 6 SW FB 3 7 VINSW GND 4 5 NC NC VFQFPN8 4x4 1.2 HSOP8 AM12893v1 Pin description Table 1. Pin description Package/pin 6/42 Type VFQFPN8 4x4 HS0P8 1 1 Description VINA Analog circuitry power supply connection 2 2 DIM Dimming control input. Logic low prevents the switching activity, logic high enables it.
LED2001 2 Maximum ratings Maximum ratings Table 2. Absolute maximum ratings Symbol Parameter 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 VINSW 3 Value -0.
Electrical characteristics 4 LED2001 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 (1) Typ. 3 Max. 18 Device ON level 2.6 2.75 2.9 Device OFF level 2.4 2.55 2.
LED2001 5 Functional description Functional description The LED2001 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.
Functional description 5.1 LED2001 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.
LED2001 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).
Application notes LED2001 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.
LED2001 Application notes Equation 2 1 ω Z = ------------------------------ESR ⋅ C OUT Equation 3 m C ⋅ ( 1 – D ) – 0.
Application notes LED2001 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.
LED2001 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 << 1 MHz.
Application notes LED2001 Figure 7. Equivalent series resistor [A] 1 working point 0.1 2 1 3 [V] 4 AM12898v1 Figure 8 shows the equivalent circuit of the LED constant current generator. Figure 8.
LED2001 Application notes As a consequence, the LED equivalent circuit gives the αLED(s) term correlating the output voltage with the high impedance FB input: Equation 14 R SENSE α LED ( n LED ) = ---------------------------------------------------------n LED ⋅ rLED + R SENSE 6.5 Total loop gain In summary, the open loop gain can be expressed as: Equation 15 G ( s ) = G CO ( s ) ⋅ A 0 ( s ) ⋅ α LED ( n LED ) Example 1 Design specification: VIN=12 V, VFW_LED=3.5 V, nLED= 2, rLED= 1.
Application notes LED2001 Figure 9. Module plot (;7(51$/ /223 02'8/( 0RGXOH >G%@ [ )UHTXHQF\ >+]@ [ [ [ [ $0 Y Figure 10. Phase plot (;7(51$/ /223 *$,1 3+$6( 3KDVH [ [ )UHTXHQF\ >+]@ [ [ [ $0 Y The cut-off frequency and the phase margin are: Equation 18 f C = 14 kHz 6.
LED2001 Application notes Figure 11. Dimming operation example AM12902v1 In fact, when dimming enables the switching activity, a small capacitor value is fast charged with low inductor value. As a consequence, the LEDs current rising edge time is improved and the inductor current oscillation reduced. An oversized output capacitor value requires extra current for fast charge so generating certain inductor current oscillations The switching activity is prevented as soon as the dimming signal goes low.
Application notes LED2001 Figure 12. LED current falling edge operation AM12903v1 6.6.1 Dimming frequency vs. dimming depth As seen in Section 6.6, 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.
LED2001 Application notes Figure 13. Dimming signal AM12904v1 For example, assuming a 1 kHz dimming frequency the maximum dimming depth is 5% or, given a 2% dimming depth, it follows a 200 Hz maximum fDIM. The LED2001 dimming performance is strictly dependent on the system small signal response. As a consequence, an optimized compensation (good phase margin and bandwidth maximized) and minimized COUT value are crucial for the best performance. 6.
Application information LED2001 The software calculates external components according to the internal database. It is also possible to define new components and ask the software to use them. Bode plots, estimated efficiency and thermal performance are provided. Finally, the user can save the design and print all the information including the bill of material of the board. 7 Application information 7.1 Component selection 7.1.
LED2001 Application information Figure 15.
Application information LED2001 Equation 27 ΔI RIPPLE ( s=j ⋅ ω ) = ΔI RIPPLE_SPEC Example (see Section Example 1): VIN=12 V, ILED=700 mA, ΔILED/ILED=2%, VFW_LED=3.5 V, nLED=2. A lower inductor value maximizes the inductor current slew rate for better dimming performance. Equation 26 becomes: Equation 28 ΔIL ----------- = 0.5 ILED which is satisfied selecting a10 μH inductor value. The output capacitor value must be dimensioned according to Equation 27. Finally, given the selected inductor value, a 2.
LED2001 Application information equivalent RMS current is equal to IO divided by 2. The maximum and minimum duty cycles are: Equation 30 V OUT + VF D MAX = ------------------------------------V INMIN – V SW and Equation 31 V OUT + VF 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.
Application information 7.2 LED2001 Layout considerations The layout of switching DC-DC converters is very important to minimize noise and interference. Power-generating portions of the layout are the main cause of noise and so high switching current loop areas should be kept as small as possible and lead lengths as short as possible. High impedance paths (in particular the feedback connections) are susceptible to interference, so they should be as far as possible from the high current paths.
LED2001 7.3 Application information Thermal considerations The dissipated power of the device is tied to three different sources: • Conduction losses due to the RDSON, which are equal to: Equation 33 2 P ON = R RDSON_HS ⋅ ( I OUT ) ⋅ D 2 P OFF = R RDSON_LS ⋅ ( I OUT ) ⋅ ( 1 – D ) where D is the duty cycle of the application.
Application information LED2001 VIN=12 V, VFW_LED=3.5 V, nLED=2, ILED=700 mA The typical output voltage is: Equation 36 VOUT = n LED ⋅ V FW_LED + V FB = 7.1V RDSON_HS has a typical value of 95 mΩ and RDSON_LS is 69 mΩ @ 25 °C. For the calculation we can estimate RDSON_HS = 140 mΩ and RDSON_LS= 100 mΩ as a consequence of Tj increase during the operation. TSW_EQ is approximately 12 ns. IQ has a typical value of 1.5 mA @ VIN = 12 V.
LED2001 Application information The inductor current ripple during ON and OFF phases can be written as: • ON phase Equation 40 V IN – V OUT – ( DCR L + R DSON HS ) ⋅ I ΔIL TON = ----------------------------------------------------------------------------------------------- ( T ON ) L • OFF phase Equation 41 – ( V OUT + ( DCR L + R DSON LS ) ⋅ I ) ΔI L TON = ---------------------------------------------------------------------------------------- ( T OFF ) L where DCRL is the series resistance of the i
Application information LED2001 of the minimum conduction time of the power element. If the hiccup current level (6.2 A typical) is triggered, the switching activity is prevented for 12 cycles. Figure 18 shows the operation of the constant current protection when a short-circuit is applied at the output at the maximum input voltage. Figure 18.
LED2001 Application information Table 8. Component list Reference Part number Description Manufacturer 1 μF 25 V (size 0805) C1 C2 GRM31CR61E226KE15L 22 μF 25 V (size 1206) Murata C3 GRM21BR71E475KA73L 4.7 μF 25 V (size 0805) Murata R1 4.7 KΩ 5% (size 0603) R2 Not mounted Rs L1 ERJ14BSFR15U 0.15 Ω 1% (size 1206) Panasonic XAL6030-332MEB 3.3 μH ISAT = 8.4 A (20% drop) IRMS = 7.3 A (40 °C rise) (size 6.36 x 6.56 x 6.1 mm) Coilcraft Figure 20.
Application information LED2001 Figure 21. PCB layout (bottom side) DFN package Figure 22. PCB layout (component side) HSOP8 package It is strongly recommended that the input capacitors are to be put as close as possible to the pins, see C1 and C2.
LED2001 Application information Figure 23.
Typical characteristics 8 LED2001 Typical characteristics Figure 24. Soft-start Figure 25. Load regulation Vin 12V Vled 7V AM12914v1 AM12913v1 Figure 26. Dimming operation Figure 27. LED current rising edge a AM12915v1 Figure 28. LED current falling edge AM12916v1 Figure 29. Hiccup current protection To maximize the dimming performan ce the embedded LS discharges C O UT w hen D IM goes lo w.
LED2001 Typical characteristics Figure 30. OCP blanking time Figure 31. Thermal shutdown protection 130 ns typ.
Ordering information 9 LED2001 Ordering information Table 9.
LED2001 10 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 10. VFQFPN8 (4x4x1.08 mm) mechanical data mm Dim. Min. Typ. Max. 0.80 0.90 1.00 A1 0.02 0.05 A3 0.20 A b 0.23 0.30 0.38 D 3.90 4.00 4.
Package mechanical data LED2001 Figure 32. VFQFPN8 (4x4x1.
LED2001 Package mechanical data Table 11. HSOP8 mechanical data mm Dim Min. Typ. A Max. 1.70 A1 0.00 A2 1.25 b 0.31 0.51 c 0.17 0.25 D 4.80 4.90 5.00 E 5.80 6.00 6.20 E1 3.80 3.90 4.00 e 0.150 1.27 h 0.25 0.50 L 0.40 1.27 k 0.00 8.00 ccc 0.
Package mechanical data LED2001 Figure 33.
LED2001 11 Revision history Revision history Table 12. Document revision history Date Revision 20-May-2013 1 Changes Initial release.
LED2001 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.
