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Analog devices improve processor system reliability

Posted: 28 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:analog devices? microprocessor? system reliability?

By Doug Sams

M41T83/93 (Click to view block diagram)

STMicroelectronics (ST) has unveiled an Advanced Analog division that offers a variety of components that support microprocessors in reducing parts counts and lowering system cost, while ensuring system robustness. The devices complement the processor and improve system reliability in all applications.

Serial real-time-clocks
Among the most popular parts in the offering are ST's serial real-time clocks (RTCs) that support both industry standard interfaces SPI and I?C.

Most of these RTC's include automatic battery switchover circuits which ensure that the timekeeping continues in the absence of system power. All can run up to and beyond 10 years in backup using ordinary Lithium coin cells. Accurate timekeeping is possible with ST's calibration features that include both oscillator frequency adjustment (analog calibration) and periodic time adjustment (digital calibration). Typically, accuracy is better than 35 parts per million out of the box, but can be dialed down to 2ppm (about 5 seconds/month) using the calibration features.

The new M41T93 (SPI) and M41T83 (I?C) include the analog calibration featurealong with digital, tooand are available in 4mm x 4mm QFN packages. They are also offered in ST's embedded crystal package with factory-programmed analog calibration of 5ppm, guaranteed after two reflows. A low cost versionthe M41T82 is a reduced feature option of the M41T83 and comes in an SO-8 package.

ST's M41T6x series of low power RTC's are designed for battery operated and handheld applications. Ultra low standby currents under 400nA ensure accurate timekeeping and long operating periods between re-charges. In handhelds, battery switchover is part of the system, eliminating the need for that feature is not needed in the RTC, thus reducing cost. At the high end, ST recently released the M41T00AUD RTC with audio. It combines an enhanced M41T00S RTC with a complete audio section including input summing amp, 8kHz low pass filter, 16-step digital gain control and 300mW bridged output amplifier.

M41T00AUD (Click to view full diagram)

The M41T00AUD is suited for many applications including all-in-one printers, handhelds, network terminals and car radios. The audio section is primarily for sounding the call progress tones during faxing and for tone generation such as beeping and chirping to prompt users to press a key or enter data, but with its low distortion and 300mW output, it easily produces broadcast quality fidelity.

Resets and supervisors
Precision voltage references provide the key element for ST's broad reset and supervisor portfolio. From basic 3-pin resets up to high-integration security supervisors, ST has something for every application.

STM6719 multi-voltage supervisor (Click to view full image)

The STM8xx series is designed for basic reset functions and includes an option for manual reset input. For improving software reliability, the STM63xx/68xx series includes watchdogs and comes in 5-pin SOT23 packages.

For multiple voltage systems, the STM67xx series includes devices capable of monitoring up to three supplies. For example, the system I/Os may all be at 3.3V, but the processor core and FPGA core each at different voltages. The STM6719 can monitor all three levels. In addition, a delayed reset input feature prevents accidental resets by requiring the button be held for a minimum duration programmable via an external capacitor.

For voltage monitoring, the STM1061 includes several voltage options suitable for a wide variety of applications. For simple applications where a signal level needs to be compared to a threshold for a go/no-go test, a simple voltage monitor will do the job and cost much less than an ADC. When used in conjunction with the reset devices, voltage monitors can be cascaded together via open-drain bussing to provide reset supervision of multiple supplies as shown in Figure 1.

Figure 1: Using voltage detectors with reset devices.

The STM1403 and 1404 offer security supervision, which is required in data protection. Over/under voltage detection along with over/under temperature monitoring and tamper detect enable users to monitor for and thwart attempts at stealing data from computer equipment and point-of-sale terminals by detecting intrusions and erasing sensitive data before it can be copied.

Tamper detect
NVRAM supervisors such as the M41ST87 combine all the supervisor features into one device, including reset, watchdog, real-time clock, automatic battery switchover for external SRAM and tamper detect.

The tamper detect circuit is fully configurable and can be set to detect a high-to-low or low-to-high transition. It can also be set for normally open or normally closed switches. It automatically records the time of the tamper event and allows the user to select one or more of the following actions:

  1. That the processor be interrupted;
  2. That the internal RAM be cleared;
  3. That the external RAM be cleared.

Having the M41ST87 in embedded crystal package on only protects against tamper and environmental conditions but allows the user to easily engineer the devices into any design, shortening development time and reducing cost.

In addition, the automatic battery switchover not only keeps the M41ST87's RTC running in the absence of power, but also can drive an external SRAM, which allows users to create their own custom NVRAM solutions. The two channels of tamper detect can be used to erase the 128Byte of on-chip SRAM and/or the external SRAM, as well as sending interrupts to the processor. Tamper detect channels also operate in backup mode, ensuring that the data is always protected.

Temp sensors
The STLM20 analog sensor comes in a tiny micro-DFN package and can be directly connected to ADC inputs. It draws less than 8?A maximum and offers 2.5C accuracy over the range of -40C to 85C.

The STLM75 transfers its temperature data digitally over I?C bus and has 150?A current draw. It also offers an accuracy of 3.0C over the range of -55C to 125C and includes the SMBus timeout feature which prevents the bus from hanging. An enhanced variant, the STTS75, adds a one-shot mode for optimizing power consumption.

For computer applications, ST offers the STTS424, which conforms to the JEDEC 42.4 standard for memory module temperature sensors and has outstanding power consumption, drawing only 200?A maximum.

Meanwhile, ST's family of silicon oscillators is designed to be of companion for many microprocessors. Featuring faster startup times than conventional crystal oscillators, these silicon oscillators are insensitive to vibration and environmental noise making them immune to problems which crystals have in certain applications.

Also, being a major player in the NVRAM business, ST offers a large portfolio of ZEROPOWER and TIMEKEEPER devices with densities from 1Kbit to 32Mbit. Besides the industry standard CAPHAT DIP packages, ST also produces the removable/replaceable SNAPHAT battery tops and matching SOICs that offer compact footprint and packaging technology.

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