AND9204/D NCL30088 and NCL30085 Safety Test Considerations www.onsemi.com APPLICATION NOTE Introduction or badly connected. It is common to expect that such open/short situations do not cause fire, smoke nor loud noise. NCL30088 and NCL30085 are controllers targeting isolated and non−isolated constant current LED drivers. These highly integrated devices are optimized for an efficient and accurate light control with a minimum number of external components. Details on their operation can be found at www.onsemi.com. These devices also tend to ease the manufacturing and compliance with safety requirements. Elements of a LED driver can be accidentally shorted, badly soldered or damaged as a result of manufacturing or handling incidents, excessive operating stress or other troubles. In particular, adjacent pins of controllers can be shorted together or a pin can be grounded R7 5.6k R11 4.7 R16 33k R8 33k C21 1n Type = Y D8 DBL105G R9 470k 0.5W C19 NC C17 100nF 0.5W R10 470k T1 FLY_XFMR 1 6 L3 2.2mH R15 2700k D4 1N4148 NCL30088 NCL30085 R32 5.6k R6 2700k ZCD VS COMP R3 8.2k J1 C7 22p SD 1 8 2 7 3 6 4 5 C10 1mF Line Voltage: 85 − 265 V rms R5 47k C13 1n 4 C8 4.7n VCC LED+ R4 10 Vout: 12 − 20V R13 47k Q1 NDD03N80 C2 47pF R14 22 R33 820 C12 100n LED− 35V 9 3 R18 NC Iout: 500 mA DRV GND Vout J3 Vds C6 4.7nF CS C18 22p 12 1000V C1 NC RN1 NB12P00104JBB D3 MURS220 C3 470mF D1 mur180 R2 24k R20 22 . D2 BAV21 C9 47mF . F1 Safety tests have been performed in an open−frame, wide−mains, 10 W, 500 mA LED driver at 25°C ambient temperature. Figure 1 provides its application schematic. The experiments have been made with NCL30088B samples (auto−recovery protection mode and 250 mV reference voltage). . C5 47nF Type = X2 R RV1 V275LA4P L2 2.2mH R29 33k Testing Conditions Vcs C4 10mF 35V R1 3 R12 3 Figure 1. Application Schematic SHORT faults were made by means of a manual switch so that SHORT conditions could be applied before and during operation. Pin floating conditions were created by inserting a socket between the board and the socket the circuit was soldered to. The appropriate pin of the intermediate socket © Semiconductor Components Industries, LLC, 2015 February, 2015 - Rev. 0 was removed to test the floating fault under interest. The manual switch gave the possibility to reconnect the NCL30088 pin. Tests were made at 25°C ambient temperature. 1 Publication Order Number: AND9204/D AND9204/D Figure 2. Shorts are Made by Means of a Manual Switch operating and recovers normal operation when the fault condition is removed. Orange “OK” labels are for tests which did not lead to an unsafe situation but caused a degraded operation, a loss of functionality and/or board/circuit damages. No red “NOK” was observed. They would have been relevant to tests leading to unsafe situations like the continuous heating of the LED driver. Recall. Below results were obtained with the application under test and discussed tests may lead to different conclusions in another application. This report is not intended to guarantee that the part can pass all safety tests in all boards and conditions since the performance can vary with respect to the application and test conditions. The purpose of this application note is to illustrate the typical behavior of the part under particular fault situations using a particular NCL30088 evaluation board, highlighting the protection functions that help pass the safety tests. It remains, nonetheless, the responsibility of the NCL30088 user to check that the system he builds using the NCL30088, properly meets the safety requirements it must be compliant with. The following table summarizes the results. Green “OK” labels are for tests which appeared to be safely managed by the circuit. Typically, the circuit stops RESULTS SUMMARY Fault Applied Before Start− up Fault Applied in Operation Comments ADJACENT PINS SHORT TESTS ZCD and VS VS and VCOMP OK OK OK The low−impedance external components applied to the ZCD pin reduce the VS pin voltage below the level necessary to enter operation (1 V typically). Hence, in our application, the circuit cannot enter operation when the two pins are shortened. If the two pins happen to be shortened while the LED driver is operating, the power supply stops operating either because a brown−out fault is detect (low line) or simply because the ZCD pin is hold above the ZCD lower threshold (high line). In both cases, the circuit recovers normal operation when the short is removed. OK If the short is made before the LED driver is plugged in, there is no operation if the line voltage is below 125 V rms (because VS pin cannot exceed the 1−V threshold). A high line, the circuit enters operation but the output current is affected as it is when the short is made in operation. If the short is made while the LED driver operates, the COMP voltage stabilizes at around 1.9 V leading the output current to be an increasing function of the line magnitude. At the highest line, the output current was 5% above target. Note that the brown−out detection function is lost in this case. The LED driver recovers operation when the short is removed. www.onsemi.com 2 AND9204/D RESULTS SUMMARY Fault Applied Before Start− up Fault Applied in Operation Comments ADJACENT PINS SHORT TESTS VCOMP and VSD OK OK Al low line, the COMP pin voltage tends to be high and the circuit stops operation as the short leads the SD pin OVP to trip. At a high enough line (leading VCOMP to be below 2.5 V), the voltage on the SD and COMP pins stabilize at the 1.3 V clamp level making the output current be an increasing function of the line magnitude. @ 260 V rms, the output is still below the target and is 5% above target at 280 V rms. The system cannot enter operation if the fault is made before the LED driver is plugged in. The LED driver recovers operation when the short is removed. VSD and VCS OK OK The CS pin low impedance prevents the SD pin voltage from rising and hence, the circuit detects an OTP condition. The LED driver recovers operation when the short is removed. OK If the short is made before the LED driver is plugged in, the circuit detects the fault condition and does not enter operation. If the short is made while the LED driver is operating, the circuit detects the fault and stops operation. Note that a 36−ms DRV pulse will take place just before the fault is detected. The application and (in particular the MOSFET and the current sense resistor) must be able to sustain the probable transformer saturation occurring during this pulse. The LED driver recovers operation when the short is removed. OK The LED driver stops operation. The LED driver is hence safe. The controller itself could survive several on/off sequences of the manual switch without apparent degradation at low and high line. Note that however, the NCL30088 driver stage is highly stressed during this test and may be damaged in some cases. OK OK The LED driver can sustain the fault at low line but is damaged at high line. At low line, the VCC capacitor can be discharged safely without board damage (several on/off of the manual switch could be made @ 90 V rms). At high line, the long time to discharge the VCC capacitor (note that there is a split VCC configuration in our board) leads to an excessive MOSFET stress. VCC and ZCD OK OK VCC and VS OK OK VCC and VCOMP OK OK VCC and VSD OK OK VCC and VCS OK OK VCS and GND GND and DRV DRV and VCC OK OK SHORT TO VCC If the short is made before the LED driver is plugged in, the internal impedance of the pin under test or the impedance of the external components applied to the pin under test, prevents VCC from charging up. Hence, the system cannot enter operation until the short is removed. If the short is made while the LED driver is operating, the pin under test is damaged and becomes low impedance. As a result the VCC capacitor is discharged and the circuit stops operating as long as the short is maintained (VCC cannot charged up). When the short is removed, the circuit behaves the same as when the tested pin is grounded (see below). VCC and DRV OK OK The LED driver can sustain the fault at low line but is damaged at high line. At low line, the VCC capacitor can be discharged safely without board damage (several on/off of the manual switch could be made @ 90 V rms). At high line, the long time to discharge the VCC capacitor (note that there is a split VCC configuration in our board) leads to an excessive MOSFET stress. VCC and GND OK OK The LED driver stops operating as soon and as long as the short is applied (no VCC voltage). The LED driver recovers normal operation when the short is removed. ZCD pin and GND OK OK The AUX_SCP protection makes the circuit enter a safe, low duty−ratio burst mode (<2.5%). Valley detection is lost during the active part of the burst. The circuit recovers operation as soon as the short is removed. VS and GND OK OK The circuit detects a brown−out fault. No excessive line current is noted during the brown−out blanking time. The circuit recovers normal operation when the short is removed. SHORT TO GND www.onsemi.com 3 AND9204/D RESULTS SUMMARY Fault Applied Before Start− up Fault Applied in Operation Comments SHORT TO GND VCOMP and GND OK OK The circuit continues operating but the output current capability is reduced. The circuit only provides 10 mA @ 90 V rms and 220 mA @ 265 V rms. Normal operation is recovered when the short is removed. SD and GND OK OK The OTP protects the application in this case. The circuit recovers normal operation when the short is removed. OK If the short is made before the LED driver is plugged in, the circuit detects the fault condition and does not enter operation. If the short is made while the LED driver is operating, the circuit detects the fault and stops operation. Note that a 36−ms DRV pulse will take place just before the fault is detected. The application and (in particular the MOSFET and the current sense resistor) must be able to sustain the probable transformer saturation occurring during this pulse. The LED driver recovers operation when the short is removed. VCS and GND OK DRV and GND OK OK The LED driver stops operation. The LED driver is hence safe. The controller itself could survive several on/off sequences of the manual switch without apparent degradation at low and high line. Note that however, the NCL30088 driver stage is highly stressed during this test and may be damaged in some cases. VCC and GND OK OK The LED driver stops operating as soon and as long as the short is applied (no VCC voltage). The LED driver recovers normal operation when the short is removed. ZCD floating OK OK The pin is naturally pulled down by a 200 kW internal resistor. The circuit behaves like if the pin was grounded. The circuit recovers normal operation as soon as the pin is reconnected. VS floating OK OK The pin is naturally pulled down by a 250 nA internal resistor. The circuit behaves like if the pin was grounded. The circuit recovers normal operation as soon as the pin is reconnected. Operation is instable. At low line, the output current is in average below the target. At high line, the output current still instable tends to be above the target. It is important to check that the OVP threshold is well adjusted so that the LED string is not overstressed. The circuit recovers normal operation as soon as the pin is reconnected. FLOATING PIN COMP floating OK OK SD floating OK OK CS floating OK OK A 1 mA current source pulls−up the CS pin and stops operation. The circuit recovers normal operation as soon as the pin is reconnected. GND floating OK OK The fault is detected and the circuit stops operation in this case. Normal operation is recovered when the GND is connected. DRV floating OK OK The LED driver is off since an external resistor maintains the MOSFET in low state (R13 47 kΩ resistor of Figure 1). OK The NCL30088 being not fed, the LED driver remains off. However, beware of two things: • The VCC capacitor is traditionally charged by means of a resistor placed between the input voltage rail and the VCC pin. If there is no VCC consumption, the VCC capacitor voltage can reach the input voltage level. If the circuit VCC pin is not connected and if no Zener diode is used for SD pin OVP or another component able to contain its rise, the voltage across the VCC capacitor can get very high • Do not reconnect abruptly the VCC pin. The excessive VCC capacitor voltage (see above bullet) and/or the high dV/dt can damage the part. VCC floating OK Normal operation but the SD pin OVP and OTP protections are lost. www.onsemi.com 4 AND9204/D As seen throughout the testing, simulated faults resulted in predicable safety responses and the enhanced safety features built in to the NCL30088 in the majority of causes resulted in events that were recoverable when the fault condition was removed. Note that as aforementioned, these tests have been made with NCL30088B samples. However, this report can help predict the expected behavior of the other NCL30088 versions (A, C, D) and also that of the NCL30085 under the same conditions by indicating the protection features in play. Note however, that some of the faults would latch off the latching−off versions (NCL30088A, NCL30088C and NCL30085A), causing operation recovery to be impossible until the LED driver is unplugged for the time necessary to reset the controller. For instance, if the NCL30088A SD pin is grounded, the OTP protection will trip and maintain the circuit off until both the fault is cleared AND the VCC voltage is discharged below the VCC(reset) level (5 V typically). ♦ ♦ Detailed information are available in the respective data sheet and application notes which can be found at: ♦ http://www.onsemi.com/PowerSolutions/product.do ?id=NCL30088 for NCL30088 ♦ http://www.onsemi.com/PowerSolutions/product.do ?id=NCL30085 for NCL30085. This report is not intended to guarantee that the part can pass all safety tests in all boards and conditions since the performance can vary with respect to the application and test conditions. The purpose of this application note is to illustrate the typical behavior of the part under particular fault situations using a particular NCL30088 evaluation board, highlighting the protection functions that help pass the safety tests. It remains, nonetheless, the responsibility of the NCL30088 user to check that the system he builds using the NCL30088, properly meets the safety requirements it must be compliant with. Recall. Below results were obtained with the application under test and discussed tests may lead to different conclusions in another application. Please further note that all NCL30088 and NCL30085 versions embed specific functions which protect the LED driver if: ♦ ♦ ♦ A winding is shorted and/or the inductor saturates The temperature is excessive. The LED string is shorted The LED string is open The output diode is shorted ON Semiconductor and the are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries. SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. 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