HVLED805

HVLED805 Off-line LED driver with primary-sensing Features ■ 800 V, avalanche rugged internal power MOSFET ■ 5% accuracy on constant LED output current with primary control ■ Optocoupler not needed ■ Quasi-resonant (QR) zero voltage switching (ZVS) operation ■ Internal HV start-up circuit ■ Open or short LED string management ■ Automatic self supply ■ Input voltage feed-forward for mains independent cc regulation SO16N Table 1. Device summary Order codes Package HVLED805 Packaging Tube SO16N HVLED805TR Tape and reel Applications ■ AC-DC led driver applications ■ LED retrofit lamps (i.e. E27, GU10) Figure 1. Application diagram Vin VCC HV start-up & SUPPLY LOGIC PROT ECTION & FEEDFORWARD LOGIC Vref DE MAG LOGIC 3.3V Vref ... 1V Rfb OCP CONSTANT VOLTAGE REGULATION COMP LED DRIVING LOGIC CONSTANT CURRENT REGULATION DMG Rdmg DRAIN Rcomp Vc ILED GND SOURCE Rsens e CLED Cc omp October 2010 Doc ID 18077 Rev 1 1/29 www.st.com 29 Contents HVLED805 Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1 Power section and gate driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2 High voltage startup generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.3 Secondary side demagnetization detection and triggering block . . . . . . . 15 5.4 Constant voltage operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.5 Constant current operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.6 Voltage feedforward block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.7 Burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 22 5.8 Soft-start and starter block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.9 Hiccup mode OCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.10 Layout recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2/29 Doc ID 18077 Rev 1 HVLED805 1 Description Description The HVLED805 is a high-voltage primary switcher intended for operating directly from the rectified mains with minimum external parts to provide an efficient, compact and cost effective solution for LED driving. It combines a high-performance low-voltage PWM controller chip and an 800V, avalanche-rugged power MOSFET, in the same package. The PWM is a current-mode controller IC specifically designed for ZVS (zero voltage switching) fly-back LED drivers, with constant output current (CC) regulation using primarysensing feedback. This eliminates the need for the opto-coupler, the secondary voltage reference, as well as the current sense on the secondary side, still maintaining a good LED current accuracy. Moreover it guarantees a safe operation when short circuit of one or more LEDs occurs. In addition, the device can also provide a constant output voltage regulation (CV): it makes the application able to work safely when the LED string opens due to a failure. Quasi-resonant operation is achieved by means of a transformer demagnetization sensing input that triggers MOSFET’s turn-on. This input serves also as both output voltage monitor, to perform CV regulation, and input voltage monitor, to achieve mains-independent CC regulation (line voltage feed forward). The maximum switching frequency is top-limited below 166 kHz, so that at medium-light load a special function automatically lowers the operating frequency still maintaining the operation as close to ZVS as possible. At very light load, the device enters a controlled burst-mode operation that, along with the built-in high-voltage start-up circuit and the low operating current of the device, helps minimize the residual input consumption. Although an auxiliary winding is required in the transformer to correctly perform CV/CC regulation, the chip is able to power itself directly from the rectified mains. This is useful especially during CC regulation, where the fly-back voltage generated by the winding drops. In addition to these functions that optimize power handling under different operating conditions, the device offers protection features that considerably increase end-product’s safety and reliability: auxiliary winding disconnection or brownout detection and shorted secondary rectifier or transformer’s saturation detection. All of them are auto restart mode. Doc ID 18077 Rev 1 3/29 Maximum ratings 2 HVLED805 Maximum ratings Table 2. Symbol VDS ID Eav Absolute maximum ratings Pin Parameter 1,2, 13-16 Drain-to-source (ground) voltage 1,2, 13-16 Drain current (1) 1,2, 13-16 Single pulse avalanche energy (Tj = 25°C, ID = 0.7A) Value Unit -1 to 800 V 1 A 50 mJ Vcc 3 Supply voltage (Icc < 25mA) Self limiting V IDMG 6 Zero current detector current ±2 mA Vcomp 7 Analog input -0.3 to 3.6 V 0.9 W Ptot Power dissipation @TA = 50°C TJ Junction temperature range -40 to 150 °C Storage temperature -55 to 150 °C Max. value Unit Tstg 1. Limited by maximum temperature allowed. Table 3. Symbol 4/29 Thermal data Parameter RthJP Thermal resistance, junction-to-pin 10 RthJA Thermal resistance, junction-to-ambient 110 °C/W Doc ID 18077 Rev 1 HVLED805 3 Electrical characteristics Electrical characteristics TJ = -25 to 125 °C, Vcc=14 V; unless otherwise specified. Table 4. Electrical characteristics Symbol Parameter Test condition Min. Typ. Max. Unit Power section V(BR)DSS Drain-source breakdown IDSS ID< 100 µA; Tj = 25 °C 800 VDS = 750V; Tj = 125 °C (See Figure 4 and note) Off state drain current 80 Id=250 mA; Tj = 25 °C RDS(on) Coss V 11 14 Drain-source ON-state resistance Id=250 mA; Tj = 125 °C µA Ω 28 Effective (energy-related) output capacitance (See Figure 3) High-voltage start-up generator VStart Icharge Min. drain start voltage Icharge < 100µA 40 50 60 4 5.5 7 Vcc startup charge current VDRAIN> VStart; Vcc VStart; Vcc>RSENSE, the previous one can be simplified as: Equation 12 VOFFSET = VIN ⋅ RFF m ⋅ R dmg Doc ID 18077 Rev 1 21/29 Application information HVLED805 This offset is proportional to VIN and is used to compensate the current overshoot, according to the formula: Equation 13 VIN ⋅ Td V ⋅R ⋅ RSENSE = IN FF Lp m ⋅ R dmg Finally, the Rdmg resistor can be calculated as follows: Equation 14 R dmg = L p ⋅ RFF NAUX ⋅ NPRI Td ⋅ R SENSE In this case the peak drain current does not depend on input voltage anymore. One more consideration concerns the Rdmg value: during MOSFET’s ON-time, the current sourced by the DMG pin, IDMG, is compared with an internal reference current IDMGON (-50 µA typical). If IDMG < IDMGON, the brownout function is activated and the IC is shut-down. This feature is especially important when the auxiliary winding is accidentally disconnected and considerably increases the end-product’s safety and reliability. 5.7 Burst-mode operation at no load or very light load When the voltage at the COMP pin falls 65 mV below a threshold fixed internally at a value, VCOMPBM, the IC is disabled with the MOSFET kept in OFF state and its consumption reduced at a lower value to minimize Vcc capacitor discharge. In this condition the converter operates in burst-mode (one pulse train every TSTART=500 µs), with minimum energy transfer. As a result of the energy delivery stop, the output voltage decreases: after 500 µs the controller switches-on the MOSFET again and the sampled voltage on the DMG pin is compared with the internal reference. If the voltage on the EA output, as a result of the comparison, exceeds the VCOMPL threshold, the device restarts switching, otherwise it stays OFF for another 500 µs period. In this way the converter will work in burst-mode with a nearly constant peak current defined by the internal disable level. A load decrease will then cause a frequency reduction, which can go down even to few hundred hertz, thus minimizing all frequency-related losses and making it easier to comply with energy saving regulations. This kind of operation, shown in the timing diagrams of Figure 19 along with the others previously described, is noise-free since the peak current is low 22/29 Doc ID 18077 Rev 1 HVLED805 Application information Figure 18. Load-dependent operating modes: timing diagrams COMP 65 mV hyster. VCOMPL IDS Normal-mode 5.8 TSTART TSTART TSTART Burst-mode TSTART Normal-mode Soft-start and starter block The soft start feature is automatically implemented by the constant current block, as the primary peak current will be limited from the voltage on the CLED capacitor. During start-up, as the output voltage is zero, the IC will start in CC mode with no high peak current operations. In this way the voltage on the output capacitor will increase slowly and the soft-start feature will be ensured. Actually the CLED value is not important to define the soft-start time, as its duration depends on others circuit parameters, like transformer ratio, sense resistor, output capacitors and load. The user will define the best appropriate value by experiments. 5.9 Hiccup mode OCP The device is also protected against short circuit of the secondary rectifier, short circuit on the secondary winding or a hard-saturated flyback transformer. A comparator monitors continuously the voltage on the RSENSE and activates a protection circuitry if this voltage exceeds 1 V. To distinguish an actual malfunction from a disturbance (e.g. induced during ESD tests), the first time the comparator is tripped the protection circuit enters a “warning state”. If in the subsequent switching cycle the comparator is not tripped, a temporary disturbance is assumed and the protection logic will be reset in its idle state; if the comparator will be tripped again a real malfunction is assumed and the device will be stopped. This condition is latched as long as the device is supplied. While it is disabled, however, no energy is coming from the self-supply circuit; hence the voltage on the VCC capacitor will decay and cross the UVLO threshold after some time, which clears the latch. The internal start-up generator is still off, then the VCC voltage still needs to go below its restart voltage Doc ID 18077 Rev 1 23/29 Application information HVLED805 before the VCC capacitor is charged again and the device restarted. Ultimately, this will result in a low-frequency intermittent operation (Hiccup-mode operation), with very low stress on the power circuit. This special condition is illustrated in the timing diagram of Figure 18. Figure 19. Hiccup-mode OCP: timing diagram Secondary diode is shorted here VCC VccON VccOFF Vccrest VSOURCE Vcsdis t 1V Two switching cycles VDS t t 5.10 Layout recommendations A proper printed circuit board layout is essential for correct operation of any switch-mode converter and this is true for the HVLED805 as well. Careful component placing, correct traces routing, appropriate traces widths and compliance with isolation distances are the major issues. In particular: ● The compensation network should be connected as close as possible to the COMP pin, maintaining the trace for the GND as short as possible ● Signal ground should be routed separately from power ground, as well from the sense resistor trace. 24/29 Doc ID 18077 Rev 1 HVLED805 Application information Figure 20. Suggested routing for converter ACIN ACIN DRAIN VDD DMG COMP ... HVLED805 GND ILED LED SOURCE Doc ID 18077 Rev 1 25/29 Package mechanical data 6 HVLED805 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 6. SO16N mechanical data mm inch Dim. Min Typ A a1 Min Typ 1.75 0.1 Max 0.069 0.25 a2 0.004 0.009 1.6 0.063 b 0.35 0.46 0.014 0.018 b1 0.19 0.25 0.007 0.010 C 0.5 c1 0.020 45° (typ.) D (1) 9.8 10 0.386 0.394 E 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 8.89 0.350 F(1) 3.8 4.0 0.150 0.157 G 4.60 5.30 0.181 0.208 L 0.4 1.27 0.150 0.050 M S 26/29 Max 0.62 0.024 8 °(max.) Doc ID 18077 Rev 1 HVLED805 Package mechanical data Figure 21. Package dimensions Doc ID 18077 Rev 1 27/29 Revision history 7 HVLED805 Revision history Table 7. 28/29 Document revision history Date Revision 14-Oct-2010 1 Changes Initial release Doc ID 18077 Rev 1 HVLED805 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. 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