Abstract: By selecting low-power devices, especially high-efficiency DC/DC converters, circuit board routing is optimized, structural-level design is optimized, and system-level power management is performed to extend battery operating time. According to the requirements of multimedia terminals, many new process devices have been selected, which greatly reduces the system power consumption.
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Keywords: low power OMAP1510 energy efficiency DC/DC converter
Handheld devices such as mobile phones and PDAs are increasingly demanding image and audio processing capabilities, and at the same time require smaller and smaller devices. These devices typically rely on a single rechargeable lithium battery as the power source. Therefore, improving processing power and reducing system power consumption to extend battery operating time are important research topics for handheld devices [1].
Reference [1] discusses low-power system design techniques with particular emphasis on reducing capacitance, reducing unnecessary switching behavior, and reducing voltage and frequency. The connections between external devices are typically larger than the on-chip connection capacitors. Experiments have shown that 10% to 40% of energy is consumed on the bus multiplexer driver. The output should be reduced and try to use on-chip resources. Simply reducing the frequency does not reduce power consumption because it takes longer to complete the same task. Reducing the voltage results in reduced performance and is compensated by the addition of parallel devices. Select a low-voltage CMOS chip, and each functional module in the chip should be able to manage low-power separately. There are two main types of power consumption in CMOS devices: static power and dynamic power. The operating power depends on the operating frequency, and the static power is independent of the operating frequency. Bias current (Pb) and leakage current (Pl) cause static power dissipation, and short-circuit current (Psc) and dynamic power dissipation (Pd) are caused by the switching behavior of the circuit. The total device power consumption P can be expressed as:
P=Pd+Psc+Pb+Pl
Pd=Caff V2 f
Ceff= C
In the above formula, V and f are the operating voltage and frequency of the device, Ceff is the equivalent switched capacitor, C is the allowable discharge capacitor, and is the activity weighting factor, indicating the probability that the state of the circuit changes. 85 to 90% of the power consumption of CMOS devices is dynamic power, and dynamic power is proportional to the square of the operating voltage. Therefore, choosing a low voltage device can greatly reduce power consumption.
1 main processor selection
Currently in handheld devices, mainly using ARM processing. The advantage of the ARM processor is its low price and low power consumption, which is especially suitable for various control functions [2]. The ARM chip uses the von Neumann structure, instruction and data address storage are uniformly addressed, and a single 32-bit data bus is used to transfer instructions and data. This architecture makes ARM control functions stronger and media processing speed slower, suitable for human-machine interfaces and communication protocols. In order to improve the media processing power, INTEL added a coprocessor on the PXA250 Xscale chip for multiply and accumulate. TI's OMAP1510 chip integrates an ARM925 core and a C55X core. ARM operates at up to 175MHz. The C55X uses a Harvard architecture with a program bus, three read data buses, and two write data buses. The C55X has two hardware multiply-accumulate units, two ALUs, and a hardware accelerator for DCT/IDCT, motion estimation, and 1/2 pixel interpolation. The working voltage is 1.6V and the video height is up to 200MHz. The C55x instruction set ranges from 8 to 48 bits, improving code density and reducing memory access times.
2 minimum microcontroller system (memory)
At present, the main memory is: SRAM, SDRAM, FRAM, EEPROM, FLASH. Since the platform often stores a large amount of data, such as operating system applications, you can choose FLASH, such as INTEL 28F128L18 [3]. 28F128L18 initial access time is 85ns, asynchronous page mode is 25ns, synchronous burst is 54MHz, can automatically enter power save mode after the read cycle is completed, chip select invalid or reset active into standby mode, current is about 50uA, asynchronous read current is about 18mA . In order to get back to the application, configure SDRAM or SRAM. Since SDRAM is larger and cheaper than SRAM, SDRAM is used for data storage. Since the system is running, the large power components are SDRAM in addition to the LCD backlight. Paying for part of the array refreshed Mobile SDRAM products is important to reduce power consumption. For example, SAMSUNG K4M28163PD-RS1L, automatic refresh current 85mA, 4 bank active burst mode is 50mA, enabling SDRAM automatic pre-charge. Thus, after each burst read and write, the bank enters an idle state, and the current can be reduced to 5.5 mA. When OMAP1510 controls K4M28163PD-RS1L, K4S56163-RR75 should be set to full page burst to reduce access time and reduce power consumption. The system often has some data with a small amount of data to be saved, and can use ferroelectric memory, such as the volume of the sound and the brightness of the LCD. If these parameters are saved to FLASH or EEPROM, the power consumption will be greater. FLASH requires a block erase. RAMTRON's FM24CL16 reads and writes at a 100V frequency of 3V power, with a current of 75uA and a standby current of 1uA. The ATMEL AT24C16 has a read/write current of 0.4 mA and 2 mA at 5 V 100 kHz and a standby current of 1.6 uA at 2.7 V. AT24CL16 byte write time is about 10ms, FM24CL16 write time is always line time, no delay, so power consumption is small. SDRAM uses different interfaces from FLASH and SRAM. When debugging the ARM interrupt service program, since the interrupt service vector is located at the low-end address, it is better to have SRAM mapped to the 0 address during debugging. Therefore, the chip select signals of SRAM and FLASH should be configurable. The SRAM is available with Cypress CY62157DV18, with a typical operating current of 10mA and a standby current of 2uA.
3 other peripheral components
The LCD display is transflective, such as the SHARP LQ035Q7DB02. Reflective LCDs have bright, high contrast in bright light conditions but require higher brightness in low light conditions. SHARP combines a reflective LCD with a back-lit transmissive LCD technology, which is used as a reflective LCD under high light conditions and 350 mW when used as a backlight-transmitting LED in low light conditions. Xilinx CoolRunner-II CPLDs use fast zero-power technology. In the handheld multimedia terminal, the image acquisition module and the sound collection module have a large amount of data. Therefore, in addition to the static power consumption, the interface voltage should be considered comprehensively, that is, the dynamic loss caused by data transmission.
4 power generation
Lithium-ion batteries are currently the most widely used lithium batteries, and rechargeable lithium-ion batteries are rated at 3.6V (some products are 3.7V). The termination charging voltage at full charge is related to the battery anode material: the anode material is 4.2V of graphite; the anode material is 4.1V of carbon collection. The internal resistance of different anode materials is also different, and the internal resistance of the coke anode is slightly larger. The discharge curve of the lithium ion battery is flat, and the termination discharge voltage is 2.5V to 2.75V. In the usual fixed-frequency DC/DC converters, there are three main types of power loss: (1) load current-related losses, including MOSFET on-resistance, diode forward voltage drop, inductor resistance, and capacitor equivalent series resistance. (2) Switching frequency related losses are MOSFET output capacitance gate capacitance and gate drive loss, etc.; (3) Other fixed losses, such as MOSFET, diode, capacitor leakage current loss. In the case of large load currents, mainly current-related power loss, in the case of small loads, mainly frequency-dependent power loss. When the load current range is wide, the frequency modulation method is more efficient [9]. Reference [10] discusses control methods for improving efficiency in intermittent conduction and connected conduction modes. Very DC/DC converters can operate on fixed frequencies or in pulsed mode at light loads. These two modes can be controlled externally by the chip (such as TI's TPS60110, PINEAR's LTC3440), or automatically controlled by the chip, such as Philips' TEA1207. If controlled by the chip management pin, it is controlled by the ARM: the ARM processor controls each function module to be powered down or idle, respectively, to measure the operating current in different states of the functional module, and according to the load current value, combined with the two modes of the power chip The efficiency curve or other circuit parameters choose an efficient way of working.
OMAP application platform requires multiple power supplies, such as 1.6V for core, 1.8V or 2.75V for FLASH, SDRAM, 3.3V for USB or analog audio, 5V for USB interface, for LCD power supply code +15V and so on. The method of boosting to 5V first, and then using the linear regulator LDO to drop to low voltages of 1.5, 1.8, 2.5, 2.8, 3.0, 3.3V, etc., is inefficient, especially low voltage. The 1.6V, 2.7V, 3.1V, and 3.3V on TI's innovator board are generated as follows: the battery voltage is 5V through the TPS60110 (four parallel outputs), and then 1.6V, 2.7V through the TPS76701 LDO linear regulator. 3.1V, 3.3V. The advantage of using cuk capacitor converter and low-dropout linear regulator chip LDO is that it does not require inductance, is convenient to use, and has low cost. Use the following methods to improve power efficiency: when the output voltage is lower than the minimum discharge voltage of the lithium battery, such as 2.5V, 1.8V, 1.6V, select a simple buck inductor converter; when the output voltage is higher than the lithium battery voltage drops to 2.5V A down-conversion chip that works well can extend the discharge time. For 3.3V, LINEAR's single-chip BUCKBOOST inductive converters such as the LTC3441f can be used to achieve efficiencies as high as 90% in the discharge voltage range of lithium batteries at loads of 200mA and 3.3V. The LTC3441 duty cycle can only reach (1-150nsXf)%. The BUCK-BOOST inductive converter can be designed. When the discharge voltage of the lithium battery drops to near or equal to the working voltage of the device, the duty ratio of the buck converter is 100%, that is, the input voltage reaches the output through the inductor, there is no switch switching, no High frequency switching loss, efficiency will be the highest. Because many chips have a wide voltage range. For example, 28F128J3A VCC=2.7～3.6V, VCCQ=2.7～3.6V; ADS7846 VCC=2.2～5.25V; LAN91C96 VCC=3.3V+10%; AT24C04 VCC=1.8～5.5V. Lithium-ion batteries have a longer discharge time at around 3.3V, which can increase power efficiency and extend battery life.
Here is the power scheme:
Lithium battery - TEA1200 (or TEA1201TS) - L1.5V (or 1.8V);
Lithium battery - LTC3441-3.3V (or 1.8V, 3.0V, 5V) (up to 96% efficiency);
Lithium battery - TEA1200 (or TEA1201TS, TPS60110) -5V (efficiency can be as high as 95%).
In handheld devices, a lithium battery is used to supply multiple voltage sources. The length of battery operation depends not only on the low power consumption of each device, the energy efficiency of the power converter, but also on the power management and software power consumption of the system.
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