Low Power Design Michael Thomas, Applications Engineer Class ID: CL01B Renesas Electronics America Inc.
Michael Thomas (Applications Engineer) 5 years at Renesas Electronics RX200 Technical Support RTOS, USB, DDLCD Customer projects (RL78, RX) Embedded Engineer at D-link (1 year) 2
Renesas Technology & Solution Portfolio 3
8/16-bit 32-bit Microcontroller and Microprocessor Line-up 2010 2012 1200 DMIPS, Superscalar Automotive & Industrial, 65nm 600µA/MHz, 1.5µA standby 500 DMIPS, Low Power 32-Bit High Efficiency Ultra Low Power and Low Voltage Automotive & Industrial, 90nm 600µA/MHz, 1.5µA standby 165 DMIPS, FPU, DSC 1200 DMIPS, Performance Automotive, 40nm 500µA/MHz, 35µA deep standby 165 DMIPS, FPU, DSC Industrial, 40nm 200µA/MHz, 0.3µA deep standby Industrial, 90nm 200µA/MHz, 1.6µA deep standby 25 DMIPS, Low Power Industrial & Automotive, 150nm 190µA/MHz, 0.3µA standby 10 DMIPS, Capacitive Touch Industrial & Automotive, 130nm Wide 350µA/MHz, Format 1µA LCDs standby Embedded Security, ASSP Industrial, 90nm 1mA/MHz, 100µA standby 44 DMIPS, True Low Power Industrial & Automotive, 130nm 144µA/MHz, 0.2µA standby 4
Enabling The Smart Society Portable and eventually wearable electronics will be a hallmark of the Smart Society and powerful, energy efficient MCUs are a key component of this future Challenge: The kind of electronics that would be pervasive in a Smart Society demand both powerful and highly energy efficient MCUs; unlike the low-current low-performance MCUs used in the past Solution: This class will show you how to determine the important MCU parameters and model the application to determine the best power vs performance tradeoff in choosing an MCU. 5
Agenda Introduction Choosing an MCU for a low power application Lab outline Run lab section 1-2 Discussion Run lab section 3 Summary 6
Choosing an MCU for a Low Power Application RL78 Performance (CPU core) 50MHz/78DMIPS 20MHz/31DMIPS@1.62V 1.56DMIPS/MHz 32MHz/40.6DMIPS 4MHz/5DMIPS@1.6V 1.27DMIPS/MHz Operating voltage 1.62 to 5.5V Power consumption 0.2mA/MHz 4uA in Sleep 1.6 to 5.5V 0.07mA/MHz 0.7uA in Sleep 7
Choosing an MCU for a Low Power Application Identify peripherals required in low power mode Determine low power numbers from data sheet Determine transition time and current draw Model the application for current draw Calculate battery lifetime for given battery capacity Parameter Wake Up Low Power Mode Current (MCU X) 3 ma 0.6uA Time 5uS (32 MHz) Current (RX200) 18 ma 4uA Time 150uS (50 MHz) 8
Lab Outline MCU SPI data Codec SPI FFT IIC LCD data LCD Sleep SPI FFT I2C Codec sends out data over SPI at periodic intervals MCU performs 128 point FFT on data Results are displayed on an LCD with a fixed refresh rate Return to low power mode until next cycle 9
Lab Outline SPI Takes 6.4 ms to acquire 128 samples at 20KHz sample rate 128/20000 = 6.4ms Assume Codec has no buffer; thus MCU has to be reading each sample as generated FFT Performed on pre-generated data I2C LCD refresh takes 58 ms over I2C Sleep Mode with RTC running chosen Sleep SPI FFT I2C 10
Power Profile Port toggle indicating first line of code executed after wake-up. Current GPIO External Trigger SW3 Wake-Up Trigger Start of SPI stage End of SPI stage Start of FFT stage. End of FFT stage. Start of I2C stage. End of I2C stage. Start of lowpower stage. 11
Measuring Transient Stage Current Low-ohm load resistor (1-2 Ohms) Voltage drop across resistor using scope probe Ammeter for steady state current Combine of these two methods for an accurate picture 12
Measuring Transient Stage Current 1 na 30 ma 200 mv 5V Continuous ranging USB $900-$1500 pocketpico.com 13
Lab Outline: Sections 1-2 Measure current draw in each stage Calculate transition times Generate power profiles Plot current vs update rate graph Determine crossover point 14
Start the Lab: Section 1-2 Please refer to the lab handout and let s get started! 15
Discussion 16
Discussion 0.2 ma 0.4 Hz MCU Maximum Update/Sec RL78 6.4 RX200 14.8 17
RX210 Operating Modes Configured via the OPCCR register Module Stop, Software Standby, Deep Software Standby Mode ICLK Max Freq. F/PCLK Max Freq. BCLK Max Freq. Flash VCC Range Limitation Read Op. P/E Op. Internal Voltage Regulator Mode High Speed Mode 50MHz 32MHz 12.5MHz 5.5-2.7V 5.5-2.7V High Power Middle Speed Mode A 32MHz/ 20MHz 32MHz/ 20MHz 8MHz/ 5MHz 5.5-1.8V/ 1.8-1.62V Middle Power Middle Speed Mode B 3.6-1.62V Low Speed Mode 1 1MHz 1MHz 250kHz 5.5-1.62V N.A. Low Power Low Speed Mode 2 32kHz 32kHz 4kHz 5.5-1.62V Ultra Low Power 18
RX210 Wake-Up to HOCO @50MHz from S/W Standby 180 ua in S/W Standby Wakeup:150 usec Flash powered ON HOCO powered ON RTC+SUBClk ON 5uA in S/W Standby Wakeup: 580 usec Flash powered OFF HOCO powered ON RTC+SUBClk ON Thus there is a time/power tradeoff choice involved that has to be made depending on the application 19
Lab Outline: Section 3 Add an extra stage to the program Account for power-down transition stage Choose a different low power mode Update graph to determine new crossover point Use battery calculator to determine battery life 20
Start the Lab: Section 3 Please refer to the Lab Handout and let s get started! 21
Discussion (0.01 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 6414 229 22
Discussion (0.1 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 699 214 23
Discussion (0.4 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 176 174 24
Discussion (1 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 70 127 25
Discussion (6 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 11 39 26
Discussion (15 Hz Update Rate) 1000 mah Battery Life (days) RL78 RX210 -- 17 27
Discussion 28
Discussion MCU 0.009 RX200 Hz Maximum Cycles/Sec Power/Cycle 7 ua sleep and 550 usec wake-up 14.5 0.162mA 186 ua sleep and 150 usec wake-up 14.8 0.157mA 3 ua sleep and 3120 usec wake-up 14.0 0.192mA 29
Discussion What other operational parameters are missing from this discussion? Response time Overlapping stages Interrupt driven stages 30
Summary How to decide which MCU is better suited to a low power application How to model an application to determine its power profile The best low power MCU is the one that best fits the application Low power comparison spreadsheet Identify relevant information in the datasheet This approach can be used to compare any number of MCUs 31
Questions? 32
Enabling The Smart Society in Review Portable and eventually wearable electronics will be a hallmark of the Smart Society and powerful, energy efficient MCUs are a key component of this future Challenge: The kind of electronics that would be pervasive in a Smart Society demand both powerful and highly energy efficient MCUs; unlike the low-current low-performance MCUs used in the past Solution: This class will show you how to determine the important MCU parameters and model the application to determine the best power vs performance tradeoff in choosing an MCU. 33
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Renesas Electronics America Inc.