Electronic Design

Looks Like Analog, Designs Like Digital

In many cases, GUI-based design tools make closing the analog loop almost as easy as closing the loop in the digital domain. One recent example is National Semiconductor's 75-V, 2.5-A LM5005 buck regulator. In the figure, a screen capture from National's Webench tool shows recommended component values for a particular set of design parameters. A bill of materials and simulation results are a few mouse-clicks away.

Texas Instruments' TPS65010 is another analog controller that enables GUI-based programming. This power-and battery-management IC fits applications powered by one lithium-ion or lithium-polymer cell that require multiple power rails for core and peripheral I/O. It also has two 200-mA low-dropout voltage regulators that can be supplied either from one of the step-down converters or directly from the battery.

The chip's I2C serial interface handles dynamic voltage scaling. It can be used to collect information on, and control, the battery charger status as well. Optionally, it will control two LED driver outputs, a vibrator driver, and masking interrupts. On top of that, it can disable/enable and set the low-dropout (LDO) output voltages. The interface can transfer at rates up to 400 kHz.

Summit Microelectronics says that it's looking at state-machine-based digital control, a la Zilker Labs. But its most ambitious products, the SMB122 and the only slightly less complex SMB118, demonstrate the virtues of a digital-control-like GUI design interface in chips with analog feedback.

The SMB122 is a nine-channel power manager for portable applications. It provides three synchronous buck converters, one configurable buck/boost converter, two boost converters, one configurable inverting/noninverting buck/boost, one LDO, and a programmable lithium-ion battery charger.

Power control/monitoring functions include digitally programmable output voltage setpoint, power-up/down sequencing, enable/disable, margining, and undervoltage/overvoltage input/output monitoring on all channels. For simpler portable systems, the 118 omits two of the outputs.

With these parts, portable-system designers can create a "platform solution" that can be modified easily via software without major hardware changes.

Another not-exactly digital approach separates control and regulation. The Linear Technology LTC2970 dual power-supply monitor and margining controller with an SMBus-compatible I2C bus interface can servo each supply's output voltage over a wide range of operating conditions. The chip's seven-channel ADC also may be used to monitor current, temperature, and supplies. Monitoring functions alert a system host about incipient failures before they occur.

See the figure

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