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Motorola's New Power Switch IC Replaces Relays and Fuses
Enables Customers to Re-Architect Systems for Improved Power Management and Reliability
| The manufacturer says . . . | ChipCenter's Paul O'Shea says . . . |
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Motorolaıs new 2 milliohm high-side power switch will help designers of power electronics systems to better manage power distribution, reduce board space and increase system reliability. The MC33982 device is a mixed-signal, multi-chip integrated circuit (IC) designed to replace electromechanical relays, fuses and discrete devices in a variety of embedded systems. The new IC is ideal for systems that require up to two kilowatts of power control such as electrical actuators in appliances, power hand tools, dish positioning systems, and marine and automotive systems. Unlike mechanical relays, the silicon solution is not as susceptible to wear, contact malfunctions or corrosion over time. One major automobile manufacturer has already signed on to use the MC33982 IC in one of its primary platforms beginning in model year 2006. "With the lowest ON resistance of any automotive-grade solid state switch commercially available today, the MC33982 enables significant power savings and less heat generation in a number of applications," said Bob Jarrett, vice president and general manager of Motorola's Analog Products Division. "Its configurability, protection and diagnostic capabilities make this new power switch an exceptional alternative to mechanical or existing solid state relays, fuses and FETs." Manufactured with Motorolaıs proprietary SMARTMOS and HDTMOS processes, the MC33982 device combines high-density, high-speed logic with precision analog and high-voltage, high-current power circuitry. The built-in protection, logic level control and various configuration and communication features of the MC33982 switch help to simplify embedded system design efforts, lower system costs, and increase system reliability. Designed to thrive in the rugged automotive environment, the MC33982 IC features an ultra-low RDSon (resistance drain to source) of 2 milliohms with a bevy of operating, protection and diagnostic capabilities. The device can be used as a simple, logic level input controlled, high side FET with the following protection features:
For more demanding applications, the MC33982 offers several additional unique and enabling features that allow designers to optimize system cost and performance. Each of the following features is accessible via the built-in serial peripheral interface (SPI):
Housed in a 12x12mm power quad flat pack no-lead package, the IC uses a minimum amount of board space while providing excellent thermal characteristics through an exposed heat-sink, and solder rather than epoxy for die attachment. The MC33982 complements Motorolaıs line of analog drivers for current control, and its microcontrollers and digital signal processors with on-chip serial peripheral interfaces.
Motorola SPS P.O. Box 17927 Denver, CO 80217 USA Motorola also offers extensive resources to help companies design just the right solution using this product. More information can be found at: Design resources or by calling 1-800-521-6247 |
Solid state has been slowly replacing electromechanical switches and relays for some time and this silicon product from Motorola is another much-needed upgrade. The MC33982 will replace electromechanical relays, fuses, and discrete circuits in power management and load control applications, and of course it wonıt be subjected to mechanical wear. It is designed to thrive in the rugged automotive environment, and features an ultra-low RDSon (resistance drain-to-source) of 2 milliohms, a logic level high-side FET with a bevy of operating, protection and diagnostic capabilities. It offers a self-protecting feature that protects itself and the load from over-current, open load, over-voltage, under-voltage conditions. For example, if someone shorts the output, the device will shut itself off. The part really works like a breaker, not a fuse, which stops operation. Working similiarly as a breaker, the part turns itself off and back on later if the conditions are favorable. However, if it still detects a problem after a period of time, it shuts itself off again. The device shuts itself off and can be interrogated by the MCU and tell you what the problem is. This is especially helpful for automotive situations when, for example, your radiator fan dies. You know when this happens because your car stops running after it overheats. This IC switch can protect the part if there is a problem because it can signal the MCU and give a warning to the user before the car goes into thermal shutdown. A couple other outstanding features of the part include a standby current of only a few micro amps, and fast switching with pulse width modulation capability, which is something you canıt get with electromechanical switches. This power switch is used with a microcontroller unit so it has distributed intelligence and provides diagnostics and self-check capability. Maybe one of the unsung features is the control of electromagnetic noise with di/dt and dv/dt - adjustable current and voltage control. For the automotive industry the most important feature will probably be the current capability on a high-side switch. However, you can buy high-side FETs in this range but the protection at this high side current range is the important feature. Another important feature is the open load detect, which tells you that something happened and the load isnıt there anymore, or for example, the "check engine" light on your dash should be turned on or the onboard computer should be alerted. The current limit is important because if the load shorts, this function prevents current from running through the device and over-heating it. Motorola says this device allows manufacturers to rethink their electrical architecture for power distribution. It allows you to separate the power into zones or functions depending on what you want to do from a wiring standpoint or a power-down perspective. For example, one of the big issues for vehicles with a lot of electronics is high current drain. Unless something is done to the electrical design, the current drain could lead to a dead car battery for a car that was left in long-term parking at the airport. So many car manufacturers are designing electrical procedures to power-down selective modules. This Motorola device can help designers power down whole sections, or zones, of the vehicleıs electronics by powering down the MCUs that are associated with these zones. A very significant feature of the MC33982 is the 2 milliohm RDSon switch, which is less resistance than some leads have. Simply put, this part doesnıt get hot. According to the company, the reason the RDSon is so low is because of the combination of the companyıs HDTMOS and SMARTMOS processes as well as some innovative packaging and assembly techniques. There are wires inside but itıs really a matter of how you attach the wires to the leads and then how the leads are brought out. The 2 milliohm switch is interesting, but you can buy a 2 milliohm FET (and it probably will be pretty big) from several companies. Unfortunately, these FETs typically donıt have any mechanism to protect them from failing when a high current passes through them. The device from Motorola checks the current from the HDTMOS process using a current sensing technique that accurately determines how much current is running through the device, without using external sense resistors. According to Motorola, this on-board technique is important because there are failure modes that can happen when an off-board FET is used to sense current, which donıt give you the level of diagnostics typically needed. A feature that you canıt get with an electromechanical relay is pulse-width modulation (PWM) capability. This technique could be used in lighting applications to dim the lights or be used to control a carıs day-time running lights. Because this device allows you to employ PWM and slew rate control, you also dramatically reduce electromagnetic interference (EMI) in the system. EMI is becoming a significant problem in industrial or automotive applications where you have lights and motors on the bus, which causes a lot of noise and possible mechanical or electrical problems. So, if you move the power capability out to where the load is and reduce the length of the wire carrying the high current spikes, you can control the slew rate and reduce the noise. So whatıs the down-side? The power IC switch costs more than an electromechanical relay. But this is a perceived difference because the relay doesnıt really cost $1 since you have to buy a driver and supplementary parts that bump the cost up to about $1.50. Additionally, mechanical relay manufacturers have pretty much squeezed all the cost out of their parts. Most of todayıs relay designs canıt be directly driven - they need a driver with some intelligence and diagnostics. Many electromechanical relays use what is called a wetting current to try to extend the life and reliability of the relays. Unfortunately, that requires another silicon chip so even if the relay only costs $1 you still have to buy additional parts to get it working. The MC33982 high-side power switch is currently available in sample quantities, with production quantities expected in the second half of 2003. Unit pricing starts at a suggested list price of $3.90 (USD) (MC33982FC) for 10,000-piece quantities. A thermal model is available to help reduce customersı system development cycle times. Additional power switches with pin count, feature set and voltage variations are expected to be announced beginning in 2003.
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