IRDC5001-LS370W Active ORing Demo Board Evaluation Procedure Using IR5001S Active ORing IC and new 100V IRF6644 DirectFET MOSFET International Rectifier * 233 Kansas Street, El Segundo, CA 90245 USA Overview This document describes how to connect and evaluate the supplied IRDC5001-LS370W Active ORing demo board. The purpose of this circuit is to demonstrate the Active ORing function for carrier-class system boards (in which two negative 48V inputs (-36V to -75V range) are OR-ed to provide redundant board power), and to show how the IR5001S can be used to implement Reverse Polarity protection for - 48V input DC-DC converters. The front side of the demo board is shown in Fig. 1. FET Check LEDs Input A+ Output+ Input B+ BUS Caps IRF6644 IR BUS converter demo boards & std 1/8 and 1/4 Brick connections IRF6644 Input A- Input B- Output- FET Check Switch IRF6644 Active ORing MOSFETs IR5001S Active ORing Controllers Figure 1. IRDC5001-LS370W Active ORing Demo Board Active ORing Demo Board Quick Evaluation Procedure The circuit schematic is shown in Fig. 2. The circuit incorporates two IR5001S Active ORing ICs (SO-8 package), and two IRF6644, 10.3mOhm typical Rds(on), 100V, N-Channel active ORing FETs, in the DirectFET MN package. The IRF644 power MOSFET's used in this circuit are capable of handling up to 370W of redundant power across a 36V to 75V range. The IRF6662, 17.5mOhm typical Rds(on), 100V, N-Channel active ORing FET is ideal for up to 200W applications, and this demo board can be International Rectifier modified to test these devices also. For lower power applications, it is recommended to use slightly higher Rds(on) MOSFET's, to enable faster response time after a reverse current is detected. As a general design practice, the active ORing FET should be selected for a Vsd drop of greater then 50mV during conduction. Eight 3.3uF, 80V aluminum capacitors are connected on the redundant bus. To evaluate the operation and performance of the active ORing demo board, connect two 48V power supplies to the input terminals (labeled Input A and Input B), and power load to output terminals. Caution: One of the IR5001S functional tests is the response to a short circuit of one of the sources. Before doing this test, it is important that the current limit function of each power supply be checked first. A safe way to test the current limit function is to set the desired current limit, then apply a short with a very low output voltage first (<5V), then remove the short, increase voltage by another 5-10V, apply the short again, and proceed with these steps until the final test voltage is reached. Extra precautions should be taken for older and larger power supplies where the current limit may not be fast enough so that shorting of the outputs can pose safety risks. To probe the circuit waveforms use an oscilloscope probe with minimal length for the ground pin and connect directly to the pins of the IC / MOSFET device. Any standard current probe & amplifier can be used to measure reverse current flow. C1 C2 C3 C4 C5 3.3uFd 3.3uFd 3.3uFd 3.3uFd N/A C6 N/A C7 N/A C8 N/A +48V Load + Load - g1 Q1 IRF6644 0Va R1 Open Open 5V G R4 Open C12 5V R3 Open D3 5V 20K C11 1.0uF G Vch S1 5V C13 1.0uF G 2 R2 Vch 510 Q2 IRF6644 0Vb +48V C10 1.0uF C9 g2 +48V IC1 1 Vline 3 4 Vcc R5 Vch 510 3 4 D2 INN FETCh GND FETst Vout IR5001S D1 +48V IC2 1 Vline 2 INP Vcc INP INN FETCh GND FETst Vout 5 6 7 8 g1 G 5 6 0Vb 7 8 IR5001S G Figure 2. IRDC5001-LS370W Active ORing Demo Board Schematic International Rectifier 0Va g2 G The procedure for checking the response tim e of the IR5001S to a simulated short circuit failure of one power source is shown in Fig. 3. T he power supply B is set at about 1V highe r output voltage than power Supply A. For e xample, VB = 49V, and V A = 48V. This guarantees that power supply B is delivering all the power to the lo ad, while power supply A is on sta nd by (has zero output current). A 150W IR2085S DC Bus Converter is used in this example on the output of the demo board. To perform the test, apply a short circuit across th e output term inals of power supply B. As the bus voltage drops below 48V (because both power supplies and the redundant bus caps are now sho rted), a reverse current will start to flow through the act ive ORing MOSFET M2 (in line with source B). The IR5001S at source B will detect this reverse current flow and will turn M2 MOSFET off in about 120nS, while allowing only 4A of reverse current flow. This is shown in Fig. 4, which also shows Vds waveform for the MOSFET M2. When the MOSFET turn s off, the energy stored in the stray leakage inductance is dissipated in the avalanche m ode that last about 20nS. The calculated avalanche energy is about 5uJ, which is negligible compared to the 220mJ avalanche rating of IRF6644. Another waveform shown in Fig. 4 is the redundant bus voltage (green trace). With 48V being delivered to a 150W bus converter load, with source B shorted, only 3V bus voltage disturbance is observed. VB VA IR2085S DC bus converter Load NO1 M1 Short circuit Current NO2 M2 Figure 3. IR Active ORing functional tests International Rectifier Applied short Vgs 4A reverse current Fet turn off Vds 0A 120ns 3A, 150W 3: MOSFET Ids (2.5A/div) 3V bus voltage disturbance 2: MOSFET Vgs, 3: MOSFET Vds; 4:Vbus Figure 4. Waveforms during short circuit test for 150W output, 48V input. Power supplies A and B were connected to the demo board with a one foot-long cable. Short circuit was applied on the output terminals of power supply B. Another unique feature of the IR5001S is that it allows system designers to assess the power redundancy status on their system boards - whether the ORing FETs are good or not. Applying a logic high at the "FET Check" pin will toggle the output of the IR5001S driver OFF. The desired outcome is that the voltage across the FET, Vds, will rise above 0.3V. When "FET check" is initiated for the MOSFET initially being on, a comparator inside IR5001S compares the Vds voltage to a reference voltage of 0.3V. If the Vds voltage is over 0.3V, the comparator sends a logic-low signal at the "FET Short" pin, indicating that the FET is working properly. This feature can be tested on this demo board via a normally-OFF switch and two green LEDs. By pressing the switch, the gate drive signals from both Active ORing controllers will be turned off, which will turn off the channels of ORing FETs. The simplest way to test this feature is to disconnect one of the power sources. For example, disconnect VB and with VA set at 48V, depress the switch. The green LED next to the IC A will turn on. If a short circuit is applied across the FET A, the LED diode will not turn on, indicating a FET short circuit. The same procedure can be used to test the ORing FET for source B (source A would be disconnected, and source B connected). In a real system, it may not be practical to disconnect one of the sources, and if the voltage of each source cannot be changed, it will only be possible to determine if one of the FETs, which is connected to a higher voltage source, is working properly or not. Usually, a truth table as shown in Table 1, can be applied to determine the status of individual FETs based on various possible status of sources A and B. Note that this table can determine not only if a FET is short, but also if it is open. For additional information on how to use FET Check feature, please contact your local IR Field Applications Engineer. International Rectifier Table 1. Truth table for IR5001S "FET Check Feature" Case 1 2 LED Initial A off on B off off A off on B off on A off off B off off A on on B off on A on on B off off A on B on 5 6 Fet A Fet B Comments Vsd of fet A > 300mV Vsd of fet B < 300mV good N/A VA>VB +0.4V Vsd of fet A > 300mV Vsd of fet B > 300mV good good IVA-VBI < 0.4V Short N/A VA>VB+0.3V Vsd of fet A < 300mV Vsd of fet B < 300mV 3 4 During the check Vsd of fet A > 300mV Vsd of fet B > 300mV Vsd of fet A > 300mV Vsd of fet B < 300mV At least one is short IVA-VBI < 0.3V N/A Short VB>VA+0.3V Open or diode good VA>VB+0.3V Open Short VA>VB+0.3V Diode N/A IVA-VBI < 0.4V Open or diode International Rectifier