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HCA600ACREF Datasheet(PDF) 10 Page - Intersil Corporation |
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HCA600ACREF Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 11 page 10 Heat Sinking The HCA600ACREF heat sink must be supplemented to achieve full power. The amount of additional heatsinking depends on the airflow. For bench testing, a small fan set up within inches of the board blowing across the shield is sufficient for full power testing. The resistors used to test the board will also likely require a fan. In applications, the internal thermal transfer plate should be bolted to the chassis. This can be accomplished by either placing the board horizontally so that the shield is in thermal contact with the bottom or side of the chassis or by using an L bracket which mounts to both the chassis and the thermal plate. The shield will not make good thermal contact with the thermal transfer plate unless a stiff piece of aluminum is bolted to the transfer plate from the outside of the shield. The reference design uses 125 mil aluminum bars for this purpose. The chassis and L bracket can also serve the same purpose, allowing the aluminum bars to be discarded. The aluminum shield is necessary for EMC compliance. Do not remove it. To ensure a long and reliable life, the heatsinking should be designed so that the module typically runs at 70oC or less. Higher operating temperatures will reduce the lifetime of the module. It is also important to use high temperature fiber washers when mounting the FETs to the transfer plate. Teflon™ and plastic washers will flow at high temperatures causing the FETs to loose contact with the transfer plate and fail. At one third power into 4 Ω (333W) the efficiency is 85%. The amplifier shuts down when the heat sink temperature is 100oC. Allowing for a temperature rise of 50 degrees above ambient, the thermal resistance of the heat sink must be approximately 1oC per watt. A fan is highly recommended. With a small fan, the existing heat sink bolted to the chassis is more than adequate. Assembly Make sure the FETs are secure, and use thermal grease on both sides of the aluminum oxide spacers. Glue the inductors down and ensure that the coils of the output choke do not run against the shield. This, may cause a short. The large inductor should be glued to the shield and the board, so that it is anchored securely. Thermal grease between the transfer plate and shield is required. Place small washers under the heatsink to lift it up off the board. The washer next to R3 requires thermal grease on both sides so that the thermistor used to sense the temperature of the thermal transfer plate will be in thermal contact. GROUNDING As in all audio amplifiers, grounding is important. The module has two ground planes, power and analog. These are connected on the board by a zero ohm jumper, R31. In most applications, this jumper should be removed, and analog ground should make one and only one connection with power ground, (star ground) - see Figure 6 for power supply transformer. AUTOMATIC RESTART INTO SHORT The amplifier is capable of distinguishing a low impedance load from a dead short. If the output is shorted with a low impedance, the amp will deliver 30A for 50ms and then shut down. If the impedance is very low (a short), the amplifier will deliver 50A for a short burst and then shut down. In either case, power must be cycled by the user to restart the amplifier. The amp will not shut down if the impedance of the loudspeaker dips, or if the speakers are momentarily shorted. In this case, the amplifier limits the current supplied to the loudspeaker. The amplifier is designed for use with 4 Ω and 8 Ω speakers. It is stable into 2Ω and 1Ω loads, but the magnetics and heatsinking are not designed for low impedance speakers or multiple speakers in parallel. If auto restart into a dead short is absolutely required, then populate R59 with a 10 Ω 805 resistor, and change C11 to a 0.1 µF, 10V, 1206 capacitor. The current limit time out will now be 5ms, and the amplifier will always try to restart after a dead short one or more times. For safety and reliability issues, if the current ramps to more than 50A on any start up attempt, the amplifier will shut down and power will need to be cycled. In this mode, unless the short is removed quickly the fuses in the power supply will blow. After the short is removed and the fuses replaced the amp will restart. Most users should not use auto restart, as it is easier for the customer to cycle power than replace a fuse. EMC COMPLIANCE AND POWER SUPPLY WIRING As with all Harris reference designs the amplifier meets both FCC and CE requirements when placed in a suitable chassis with appropriate use of by-pass capacitance. The audio input requires a 1000pF NPO capacitor to chassis, and the +speaker cable requires a 0.047 µF 200V NPO or X7R capacitor. The negative audio input and speaker return should be grounded to the chassis. A power line filter is also required to meet conducted emission specifications. SHIELD 125 mil BARS TRANSFER PLATE PC BOARD FIGURE 7. HCA600ACREF Teflon™ is a trademark of E. I. Du Pont De Nemours and Company. |
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