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Motorola Introduces Flexible I/O Expansion IC for Microcontroller-Based Systems

One IC adds switch monitoring, LED and FET drivers, and programmable wake-up to low-pin-count MCUs.

The manufacturer says . . .

ChipCenter's Paul O'Shea says . . .

With the MC33993 integrated circuit (IC) from the Motorola Semiconductor Products Sector, designers of multivoltage embedded systems now have an enhanced option for expanding the capabilities of low-pin-count microcontrollers (MCUs). The MC33993's combination of flexible input and output features gives system designers the opportunity to eliminate dozens of discrete and standard linear ICs. In many systems it may be the only device needed besides the MCU and a 3-pin regulator. The MC33993 interfaces with an MCU through a four-pin serial peripheral interface (SPI), potentially increasing the MCU input/output (I/O) signals by more than five times. By using the analog multiplex feature of the device, up to 22 analog signals may be sent to one MCU A/D converter input. For greater flexibility, the device's 22 I/O pins may be configured to: detect the status of a switch contact, either opened or closed; provide an analog value to a buffered output; drive a light emitting diode (LED) or the gate of a field-effect transistor (FET); or provide switched power to a low-current sensor. The device is also designed to allow logic-level MCUs to interface directly with system voltages from -14 V to 26 V. This makes the device ideal for a wide variety of automotive, industrial, and commercial applications. In addition, the MC33993 features a low-current sleep mode. A variety of programmable wake-up options allow the whole system, including the MCU, to operate in a low-quiescent-current state. This is an important feature for systems such as remote monitoring where current consumption is a critical design factor. Systems using higher pin-count microprocessors or microcontrollers may also benefit from the high level of integration and reduced parts count the device can enable. The MC33993 offers a wide range of features including: 22 switch inputs—14 switch-to-ground inputs and 8 programmable switch-to-power or switch-to-ground inputs Digital multiplexing via the SPI 22 to 1 analog multiplexer Contact wetting for switch reliability Multiple device connection in daisy-chain fashion using the SPI Switch pins capable of driving LEDs or external FETS 25 kV ESD (electrostatic discharge) capable Low-power wake-up on switch-state change Timer for wake-up 3.3 V and 5 V I/O MCU interface Manufactured with Motorola's SMARTMOS™ manufacturing process, the MC33993 device combines high-density, high-speed logic with precision analog and high-voltage, high-current power circuitry. Switches are found in virtually every electronic product or system from automotive dashboard displays to computers to vending machines. The MC33993 is suited for virtually any system or product in which multiple switches are used. In many systems, designers use resistors and capacitors to interface switches to the system's MCU. These passive components step down the voltage to MCU-level inputs, provide transient filtering, and protect the MCU from electrostatic discharges. The MC33993 eliminates these passive components while offering a wider input voltage range and greater MCU protection. The device is also designed to provide a contact-wetting current to the contacts of the switch. The wetting current acts as a contact cleaner, eliminating oxide build-up, which would otherwise change the integrity of the switch. This is especially useful in products or systems such as industrial switch panels or in outdoor installations and other harsh environments. The contact-wetting feature can be used to provide up to 16 mA of output current to each of the switch input pins. This allows the device to drive LEDs, the gates of FETs, or provide switched power to sensors or other devices in the system. Web: www.motorola.com/semiconductors

This is a product that is hard to define or categorize. Internally, Motorola calls this a multiple switch detection interface. That's an engineering-sounding term that probably misses a large chunk of applications it can support. Another description for the part is expansion IC. It complements or expands an MCU's capabilities. It is especially appropriate for low-pin-count MCUs because it provides an efficient means to expand system I/O capabilities. Additionally, and very important to today's designers, it can replace numerous, discrete, and passive ICs, and thereby greatly reduce board space. The MC33993 works in conjunction with an MCU and allows the user to interface the varying voltages on a system with the logic levels on the MCU. Originally, Moto targeted this at interrogating switches or relays to help figure out what's going on in a mechanical function and then tell the MCU about it. However, over the course of the design the company realized that the design and system teams built many features into the chip that turned it into much more than a switch-detection IC. For example, it has the ability to interface to very high micro-type voltages, and can go up to 26 V operating conditions. It can handle up to +40 V and down to -14 V on the input. click for full-size schematic The chip can take up to 22 signals and multiplex them to a single line in the MCU as a digital signal. It can also perform an analog multiplex and do an analog representation of the signal. This part looks like it would be ideal for 8- and 16-bit MCUs that don't have enough pins. It can take up to 22 input lines and multiplex them into the MCU, and turn around and output the signals on the same lines. For example, it could drive an FET or an LED signal. That's why it's thought of as an expander IC. Another feature that's really cool is the 25 kV ESD protection. So, it's just the part to add as an interface to your MCU and clean up a noisy environment. Rather than cleaning up the surrounding electronics environment, you can use this part as an interface between the environment and the MCU. The target applications would be for anywhere you are trying to make inputs through switches or contactors or keypads. Moto thinks it's optimized for industrial or automotive applications. For example, if you have a keypad out on an assembly line, this part can handle the noisy interface (like spikes and high voltages that the normal logic level can't handle) for the user, and it provides a rugged interface for the user. I know some of you are asking how much it costs, and comparing it to the really inexpensive MCUs that cost around one dollar. This part costs $1.63 in 10k quantities, so it is more expensive. Why not, you say, just connect another inexpensive MCU? That's probably okay, but it doesn't provide the direct-drive capability of the high-voltage interface, and probably isn't appropriate for noisy industrial or automotive environments that may need something other than 3.3 or 5 V, or for uses where a motor can cause high voltage swings on the line. It means you have to decide if you need the extra functions this part offers, like being able to go to sleep and then wake up from a switch contact. For example, you can have the IC wake up on a contact close or open, or the IC wake itself up every certain amount of time and poll everything and then go back to sleep if nothing has changed. You can also have it wake up a controller or have it wake up from an MCU signal. Remote metering stations could use this by powering a few sensors and looking for a change of state on input causing it to wake up and tell the control system that something is happening and that it has to transmit. A real good example would be security systems—the security box has a control panel at the front end and you have a backup battery. The programmable wetting feature also has the capability of disabling the timer. The wetting can source a higher amount of current at the first look at the contact, and then reduce it to a lower level current, with either 2 mA or 16 mA levels available. So Moto put in a feature that allows you to turn the timer off so that when you look at the contact you will have 16 mA flowing, which allows you to run an LED driver or turn on the gate of a FET. As you know, surrounding every MCU and embedded devices are several dollars of analog components. Typically, designers use things like a voltage regulator, serial I/O device, a sensor interface, a couple of op amps, and a few discrete packages, a watchdog timer, and a power-up monitor. By the time you complete the design you have maybe 6 to 10 components, as well as the I/O, surrounding the MCU. This MC33993 package helps you reduce this to one package and three or four pins on the MCU, such as the SPI port and an A/D converter port. The cost is comparable, but just as important, you save board space. Using this one chip is easier than using several chips because now all you need is a simple SPI routine to get the data and manipulate it in a register. You can run a 24-bit SPI message to monitor the contacts or write data. You can create a 24-bit SPI message from a C program and send it, and that's all you need to do. Then you can run multiples of these with either a daisy-chain, or you can drive them in parallel. The MC33993 multiple-switch detection interface IC is housed in a 32-lead SOIC (small-outline integrated circuit) package, and is currently available in sample and production quantities. Unit pricing starts at US$1.63 (suggested list price) for 10,000-piece quantities. An evaluation board and kit is available now. It comes with a device, some switches, and LEDs. It also has a serial interface to talk to it over the SPI that Moto calls SPIGen. It's a Visual Basic program that allows the user to send SPI messages from a PC to any SPI-controlled device. It allows you to send whole word commands, select bits and registers, and then send them, or you can log a sequence of commands to send, allowing you to do exhaustive testing. Just in case you're wondering, Moto didn't connect the MCU on the evaluation board because you can connect almost anything to the board. The evaluation board (part number KIT33993DHEVB) is available now for US$99.00 (suggested list price), and includes graphical user interface software and documentation. Datasheet

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