Rohm has unveiled a series of 16-bit microcontrollers designed for power supplies with hybrid analog-digital control loops, accompanied by evaluation boards with software.
"In recent years, medium-power power supplies have been required to provide reliability and precise control that are difficult to achieve with analog configuration alone," Rohm stated. "On the other hand, fully digital controlled power supplies offer fine control and settings but are not widely adopted in the medium and small power range due to the high power consumption and cost of digital controllers."
Targeted at industrial power supplies ranging from 30W to 1kW, the new MCU series, ML62Q20xx, "offers the same functionality as fully digital controlled power supplies but with lower power consumption and costs comparable to analog power types," according to Rohm.
The series includes four models, featuring either 16KB or 32KB of memory, packaged in 20-pin TSSOP (6.5 x 6.4mm) or 24-pin WQFN (4 x 4mm) enclosures. All models come with 2KB of data RAM and 4KB of data flash.
The 16-bit CPU is a 16MHz nX-U16/100 (A35 core) produced by Lapis Semiconductor, a Rohm subsidiary, with an on-chip phase-locked loop generating a local 64MHz clock for pulse generation.
In addition to seven timers, these ICs feature a five-channel 12-bit 1.375μs ADC, voltage reference, programmable gain amplifier (4x, 8x, 16x, 32x), three analog comparators, and two 8-bit DAC channels. For functional safety, they include RAM parity error detection, unused ROM area access reset, watchdog, ADC testing, UART loopback, I2C loopback, and GPIO testing.
The evaluation boards, "LogiCoA001-EVK-001" and "REF66009," implement a 160kHz synchronous DC-DC buck converter with a 12V or 24V (8-38V) input and an adjustable 1-8V output, up to 5A.
Input and output voltages are monitored through ADC channels, while the main switch current is monitored by another ADC channel. Fast fault response is achieved through one of the comparators.
DAC output is used to set the voltage for an external error amplifier (the first lever for the MCU-controlled DC-DC converter) and as a reference for the fast-response overcurrent comparator.
The voltage feedback loop uses analog compensation from an external error amplifier, with the resulting voltage fed into an internal comparator in the MCU. The output of this comparator controls the "on" time of the main MOSFET switch.
Another input to the comparator is a replicated voltage ramp, controlled by the MCU (the second lever), generated on an externally powered capacitor, which is periodically shorted by a pulse waveform from the MCU.
"Using microcontrollers allows many parameters such as output voltage set value, dead-time set value, and protection circuit set value to be changed via software, similar to fully digital control," Rohm noted, while also acknowledging, "the response characteristics of the output voltage are not as good as fully digital control due to the use of an analog compensator."
The software also allows for the storage of non-volatile factory calibration values, error logging for future analysis, and adaptive control of parameters such as dead time.
"Rohm will continue to develop MCUs supporting various power topologies," the company stated.
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