The intent of the smart grid is to allow communication through the power supply to increase the efficiency of the energy grid. This is achieved by ensuring that any equipment connected to the power grid will not only be power efficient for the intended functionality, but will also use the energy in the most efficient manner, minimizing peak power consumption and average overall power usage.
In order to achieve this level of efficiency, a power efficient M2M communication system is required. At the heart of the system is a microcontroller such as the ultra-low power MSP430 MCU. To minimize the impact on the M2M communication system efficiency, without transmitting, it is critical to optimize the power supply of the MSP430 MCU. One way to do that is through a dynamic voltage scaling technique.
Using a dynamic voltage scaling (DVS) technique can minimize power consumption by lowering quiescent current in the system.
Although LDOs are not renowned for their power efficiency, they can, if used appropriately, increase the power efficiency of a system. This power efficiency increase is achieved by reducing the clock speed of the MCU by reducing the supply voltage. As the supply voltage is reduced, there is the additional advantage of reduced quiescent current further reducing power consumption.
Figure 1: MSP430F21X1 Minimum Operating Voltage vs. Clock Frequency
Since the MCU may only require peak performance during a predetermined time such as transmission, but not while monitoring other functionality of the system, implementing DVS can reduce system power consumption.
LDOs such as TPS780 make it easy to implement an integrated DVS solution.
Figure 2: TPS780 DVS Implementation
Other DVS solutions are possible by using ANY-OUTTM LDOs such as the TPS7A83. ANY-OUTTM LDOs can achieve 255 different voltages with a 50mV or 100mV resolution. (Please refer to “Increasing resolution for ANY-OUT programmable output voltage devices” for additional information or individual device datasheet for more information) ANY-OUTTM devices have a 1A drive capability, so it would be overkill for an MSP430 MCU, but may be of interest for other higher-power circuitry requiring DVS.
Another alternative is to use two independent LDOs connected as shown in figure 3.
Figure 3: DVS using two fixed output LDOs
Enabling the high-Vout LDO forces the low-Vout LDO to stops its regulation. Disabling the high-voltage LDO allows the low-voltage LDO to regulate again. Transition from one LDO to the next is shown in figure 4.
Figure 4: Transition from 3.3V LDO to 1.8V LDO
Monitoring those power supplies and ensuring that no overvoltage condition is present in the system will require the use of voltage supervisors. The TPS3831 with its extremely low quiescent current and small footprint is ideal for this task.
Figure 5: TPS383x as MCU supervisor
For multiple voltage monitors integrated in a single package, the TPS386000 is the best candidate for integration and independent delay times.
Figure 6: TPS386000 Example Circuit
LDOs and supply voltage monitors are an essential part of managing power supply and ensuring that smart grid systems are operating at high efficiency. If you have any questions about the DVS technique, please let me know in the comment section below!
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Hi Xavier, When you reduce the voltage supplied for MSP430, is the clock reducing automatically ? Is the clock devices inside MSP430.
Thank you for your post. Regards Ahmet.
Thank you for your comment Ahmet.
I am not a spcecialist in MSP430, but I do not believe that the clock is reduced automatically when the supply voltage is decreased. You do have the option of using a VCO but those have typically been developed for RF type of applications where low jitter clocks and accurate frequency are required by the system.
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