Innovative Architecture for Lowest System Power Consumption

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1 Innovative Architecture for Lowest System Power Consumption Abstract Innovative architecture for lowest system power consumption. Reducing the power consumption is in every designer mind. Today two trends are evident: LED lighting finds its way into the households replacing incandescent an fluorescent bulbs Smart control of the light, key words: home automation, motion detection, presence detection With introducing LEDs the power reduction made a quantum step andhave potential to get more efficient over the coming few years. Consider that light is needed just a fraction of the day the stand-by power accounts for a remarkable share of the total power needs. The following approach addresses this by looking into the system architecture. The combination of an ultra low power real time clock () communicating the system microcontroller can make the difference. Landscape The automation is finding its place not only in high-tech building, but penetrates now to offices and homes. Smart home, connected home are key words in this field, managed by central control unit with a smart user interface. In the basic versions dominantly on-off functions were controlled. Meanwhile distributed intelligence is optimal to control the parameter at the spot of use or occurrence. One of the key applications is the ambient light control in a room or in a section of the room. The criteria for light control are: Light needed: automatic control during active hours e.g. working hours Light wanted: user wants to turn on the light Light intensity: use only as much light as needed to be comfortable Ambient light: account for ambient light coming from outside, less LED light near the window, compared to back in the room These functions are for instance easily delegated to a small controller near or in the light fixture. Extremely low system Power consumption enabled by lowest power real time clock: By Markus Hintermann markus.hintermann@nxp.com After looking in the physical placing, let s look focus on the timing aspects. The different tasks of a lighting system to cover: We want to be able to turn on the light with no sensible delay In the off time or stand-by time the power consumption should be ideally zero Most of the time the power should essentially be (almost) switched off To resolve the first point the microcontroller must be initiated to perform the task in reasonable time triggered from the light switch, entry senor or from the central home controller. For doing this we can allow to take time of some hundreds of milliseconds. Essential: it is not required to be able to activate within a fraction of a microsecond. The human eye cannot sense it much faster, respectively a small delay isn t deranging.

2 Architecture The activation rhythm is typically controlled by system microcontroller. It is selected to perform the task optimally. The request to reduce power consumption is followed, but it in most cases there is room to cut it down even further, but how and at what cost? In principle stay in power down and just check periodically for actions to execute. Figure 1. Basic Blocks Estimate the on / off ratio of the system. In many cases the on time is magnitudes smaller than the off time. Therefore saving power during the off-time is key. The use of an ultra low power s enables to totally new system architecture. It allows to cut the system power consumption to a minimum. What are the main elements? In most systems the microcontroller is using the on-chip and runs in power down mode. It typically uses still 2 10μA (fig. 2). By transferring the authority to the ultra low power the microcontroller can be set to hibernation mode and just some 0.1μA are used to keep the running. The wake-up pattern can be programmed optimally to suit the application. Control Panel Lighting Alert / Room Shutter LCD driver LED driver Temp sense Motor control Figure 2. Conventional Architecture Today are real time clocks from different vendors on the market, which can take over the wake up task at lower power than with the on-chip of the microcontroller. In the optimal solution we have the real time clock powered separately from the microcontroller. Control Panel Lighting Alert / Room Shutter LCD driver LED driver Temp sense Motor control Figure 3. Innovative Architecture

3 Components: Features and Selections NXP has a long tradition in offering real time clocks (). Key features are easy to interface (I2C-bus or SPI bus), high temperature (125 C) high accuracy (±5ppm) and low power. The latest products allow innovative solutions, since the power consumption has been dropped to an industries best performance of 0.15μW requiring just 100nA. V BAT V SUPPLY at The PCF2123 and PCF8523 offer a freely programmable alarm and timer function that gives the designers the option to generate a wake-up signal on an interrupt pin. A programmable offset register also allows fine-tuning of the clock. The seconds, minutes, hours, days, weekdays, month and years registers are all coded in BCD format for easy conversion to decimal digits for printing or display an faster decimal calculations. The PCF2123 and PCF8523 offer a freely programmable alarm and timer function that gives the designers the option to generate a wake-up signal on an interrupt pin. A programmable offset register also allows fine-tuning of the clock. The seconds, minutes, hours, days, weekdays, month and years registers are all coded in BCD format for easy conversion to decimal digits for printing or display an faster decimal calculations. Data is transferred serially via SPI bus with a maximum data rate of 6.25Mbits per second (PCF2123) or with 1MHz fast mode Plus I2C-bus (PCF8523). Lowest power is achieved with a quartz crystal with CL of 7pF. Operation with the low cost 12.5pF quartzes is also guaranteed. V th(sw)bat =2.5V Figure 4. Standard mode V BAT V th(sw)bat =2.5V V SUPPLY at Figure 5. Direct Switching Mode The PCF8523 has additional features to reduce complexity in the application: Battery back-up circuit, the standard mode (fig. 4)is suitable when the standard supply voltage is larger than the battery back-up voltage. In addition we have integrated a new so called direct mode (fig. 5) to cope with the latest architecture and batteries. With the move to 3V supply and the rising popularity of the high density lithium batteries (with typical voltage of 4V) the direct mode allows switching in the battery at the latest possible moment to conserve its charge. The status of the different functional blocks can be configured as interrupt signals or read as flags in the status registers: timer, watchdog, alarm or battery switch-over To be able to easily separate the interrupt of the timer, watchdog and alarm, we have added in the TSSOP14 version a second interrupt pin.

4 Components: Features and Selections The PCF2123 comes next to the TSSOP14 also in the space saving HVQFN16 of just 3mm x 3mm x 1mm and as chip scale package CSP with gold bumps: 1.5mm x 1.5mm x 0.20 mm. Quartz 32kHz Oscillator Divider Clock out CLKOUT Battery backup switch Clock calibration offset & CLKOUT /INT1 Poweron reset System control I 2 C BUS I2C-bus interface Real-Time Clock Alarm Watchdog Interrupt control PCF8523 INT2 V SS Timer 1, 2 Figure 6. Block diagram of lowest power PCF8523 Internet links:

5 Benefits Achieved lowest system power consumption. s are key elements for the system timing. Independent from the microcontroller they are immune against locking up e.g. due to endless program loops. Timers, alarms and watch dogs are independent of microcontroller interrupt levels and priorities and feature therefore continuous and constant accuracy. Supplying power to the can now be of much smaller size than with. The consumption of just 100nA can be supplied by different sources: capacitor, Supercap, coin-cell battery, or harvested form transmission signals. Type Capacity / Voltage Autonomy 8523, 2123 Autonomy with competitor 300nA Autonomy with 3uA 10μF 5V >>> 1.5V 350 seconds, 6 minutes 117 seconds, 2 minutes 12 seconds 0.1F 3.3V >>> 1.5V 500 hours, 21days 166 hours, 7 days 16 hours, <1day 1F 3.3V >>> 1.5V 208 days, 7 month 69 days, 10 weeks 7 days, 1 week Silver oxide V377 (watch) Ø 6mm 1.55V, 27mAh >15 years* 10 years 1 year Li-Ion CR2032 Ø20x3.2mm 3.6V 40mAh >15 years* 15 years 1.5 years AAA alkaline Ø10.5x44mm 1.5V 1200mAh Forever* >15 years* 4.5 years Summary The combination of an ultra low power real time clock () PCF2123 or PCF8523 with the microcontroller will reduce the power consumption in stand-by mode by up to a factor 30.