New DC-DC Switch Converter Design: Extend Lithium Battery Life in the DSP system

ଲେଖକ: ଆଇଫ୍ଲୋପାୱାର - Портативті электр станциясының жеткізушісі

Introduction For a long time, a challenge for designers in MP3 players, personal media players, digital cameras, and other portable consumer applications is to achieve high performance and low power consumption of products. These battery power systems typically use embedded digital signal processors (DSP), when the system processes multimedia application tasks, the DSP can achieve maximum processing power, and when the system is in sleep mode, the DSP has the smallest power consumption. Battery life is a very important indicator in hand-held products, and product success is directly related to the efficiency of the power supply system.

One key component in such systems is a buck-down DC-DC switch regulator that can efficiently obtain lower supply voltages from higher voltages, such as obtaining 1V supply voltages from 4.5V. As a regulator, it must maintain a constant voltage, and can respond quickly to the change of the input voltage and the change of the load current.

This article will discuss the architecture with excellent voltage regulatory performance and the advantages of high efficiency and rapid response. Switch Regulator Parametric Figure 1 shows a typical application circuit of ADI ADP2102, which is a low duty cycle, 3MHz synchronous rectifier step-down converter. The ADP2102 has a plurality of configurations that have a fixed output voltage and an adjustable output voltage.

Here, the ADP2102 is connected to a fixed output voltage configuration, and 300mA, 0.8V output voltage appears from 5.5V input voltage.

Next, give an application example of an output voltage adjustable. Figure 1. Using the ADP2102 0.

8V input from 5.5V output This will simply explain the working principle of the circuit: compare the voltage division voltage of the DC output voltage and the internal reference source in the error amplifier, then the output and current sampling of the error amplifier The output comparison of the amplifier to drive single stable trigger. Single-stable trigger is temporarily steady during the time period determined by VOUT / VIN.

Single-stable triggers turn on the above-faced transistors, and the current in the inductor L1 gradually becomes large. When the temporary steady state of a single steady trigger, the transistor is turned off, the current in the inductance L1 gradually becomes small. After the time interval determined by the minimum shutdown time, the time interval determined by the current ("Valley Value"), the single-stable trigger is triggered again.

Single-stable trigger on the chip uses input voltage feedforward to maintain a constant frequency during steady state. This oscillation is continuously carried out at an uncertain frequency (approximately 3 MHz), but is deviated from the frequency in response to the transient variation of the line and the load, and the output voltage is kept constant, and the average value of the inductor current is maintained at Output load to be loaded. The method described above is relatively novel.

Over the years, the important way for DC-DC transform is the constant frequency peak current method, and when the method is implemented in a buck DC-DC converter, it is also referred to as rear edge modulation. For detailed description of this method, an evaluation of its excellent disadvantages and a constant on-time valley current mode converter described above, refer to other technical articles. The ADP2012 also has undervoltage locked functions, soft start functions, overheating protection functions, and short-circuit protection, and has ± 1% feedback accuracy.

The architecture enables the main switch on the on-circuit time as low as 60 ns or less. Figure 2 shows a typical waveform under different conditions. Figure 2a shows a low duty cycle when ILOAD = 600mA, the voltage is reduced from VIN = 5.

5V to Vout = 0.8V. As shown in the figure, at 3MHz switching frequency, 45ns minimum on-time can be obtained.

Figure 2b shows the load current and inductor current waveform when the load current is increased by 300mA. Figure 2C shows the load current and inductor current waveform when the load current suddenly 300mA. Figure 2D shows that there is no second harmonic oscillation when the duty ratio is 50%, and the use of peak current mode is controlled when designing.

When the duty ratio is greater than or less than 50%, there is no harmonic oscillation. Figure 2A.VIN = 5.

5V, Vout = 0.8V, minimum on time = 45ns Figure 2b. Successive load transient response (iLoad = 300mA) Figure 2c.

Sudden load transient response (iLoad = 300mA) Figure 2D. Duty cycle = 50%, VIN = 3.3V, VOUT = 1.

8V, ILOAD = 300mADSP Application Dynamic Voltage Adjustment In the portable application using DSP, the core voltage and I / O voltage of the switch converter are typically supplied by the switch converter. This is to use the high efficiency DC-DC converter for battery power supply applications. The voltage regulator supplied to the kernel voltage must be able to dynamically change the voltage based on the clock speed of the processor or dynamically change the voltage according to the software.

In addition, the small size of the overall solution is equally important. What is described here is that the internal regulator of the Blackfin® processor is replaced with an external high-efficiency regulator in the application of the battery. Moreover, the control software for external regulators is also described here.

The power consumption of the dynamic power management processor is proportional to the square of the working voltage (VCORE), and is proportional to the operating frequency (FSW). Therefore, the reduction frequency can cause the dynamic power consumption to decrease, and reduce the core voltage to reduce the dynamic power index. In applications where power-sensitive applications, when the DSP simply monitors the system activity or waits for external trigger signals, the clock frequency is changed if the power supply voltage is constant, which is very useful for reducing power consumption.

However, in the application of high performance battery, only change frequencies and cannot save energy significantly. The Blackfin processor and other DSPs with advanced power management functions may change the kernel voltage and frequency in turn, thereby achieving optimal battery utilization in any case. The voltage regulator of the dynamic voltage in the ADSP-BF53x series Blackfin processor is usually implemented by internal voltage controllers and external MOSFETs.

The advantage of this method is that the single voltage (VDDext) can be applied to the DSP subsystem, and the desired core voltage (VDDINT) obtained from MOSFET. The internal nuclear voltage can be controlled by the internal register to facilitate control MIPS, and finally control energy consumption, thereby achieving the optimal battery life. In order to complete the BLACKFIN internal regulator method, an external MOSFET, Schottky diode, large inductance, and multiple output capacitors, the price is relatively expensive, the efficiency is very poor, and the occupied PCB board area is relatively large.

This brings a lot of contradictions to the system designers, and use large inductors and capacitors in the integrated regulator, which is not conducive to the portable equipment hopped by consumers. The efficiency of the integrated regulator controller is relatively low, usually only 50% to 70%, so the method is not suitable for high performance handheld battery power applications. External regulation passes the design method of the new DC-DC switch converter, the efficiency of the Blackfin integrated method itself is increased to 90% or higher.

Moreover, the size of the external component can be reduced when using an external regulator. You can also use a variety of dynamic voltage adjustment (DVS) control methods, including switching resistors (which can be implemented by DAC in some cases) and pulse width modulation (PWM) (which can achieve the same accuracy as internal methods). Regardless of which method is used, it must be able to change the voltage regulated level by software control.

The above voltage regulator control method is integrated in the internal regulator, and in external regulation must be achieved by the external device. This article describes two methods for adjusting the DSP kernel voltage using the ADP2102 synchronous DC-DC converter. When the processor runs at a low clock speed, the kernel voltage can be dynamically adjusted from 1.

2V to 1.0V. The ADP2102 high-speed synchronous switch converter can make the kernel voltage to 0.

8V when power is powered by a battery voltage of 2.7V to 5.5V.

Its constant conduction time current mode control and 3MHz switching frequency supply excellent dynamic response, very high efficiency and excellent source adjustment rate and load adjustment rate. Higher switching frequency allows the system to use ultra-small multi-layer inductance and ceramic capacitors. The ADP2102 uses 3mm × 3mmlFCSP package, saving space, only three or four external components.

And the ADP2102 includes a perfect function, such as various security features, such as undervoltage lockout, short circuit protection and overheating protection. Figure 3 shows a circuit that implements DVS. The 3.

3V power supply on the ADSP-BF533EZ-Kitlite® evaluation board is powered by the buck converter ADP2102, and the output voltage of the ADP2102 is set to 1.2V using external resistor divider R1 and R2. DSP GPIO pin is used to select the desired kernel voltage.

Changing the feedback resistance value can adjust the kernel voltage within 1.2V to 1.0V.

Through the resistance R3 in parallel with R2, the N-groove MOSFET can modify the voltage divider. Compared to R3, IRLML2402's Rdson is small, only 0.25Ω.

3.3V GPIO voltage is used to drive the gate of the MOSFET. In order to achieve better transient performance and improve the load adjustment rate, the feedforward capacitor CFF is added.

Figura 3. Dynamic voltage adjustment of ADP2102 using external MOSFET and BlackFinPWM Control About Dual Level Switch, General Application Requirements: DSP Nuclear Voltage (Vout1) = 1.2VDSP Nuclear Voltage (Vout2) = 1.

0V Input Voltage = 3.3V Output Current = 300mA uses high resistance to minimize power loss. The effect of feedforward capacitance reduces the gate leakage capacitance during the switching process.

By using a smaller feedback resistance and a larger feedforward capacitor, the transient process can be minimized, but this is at an additional power consumption. Figure 4 shows the output current IOUT, the output voltage Vout, and the control voltage VSEL. When VSEL is low, the output voltage is 1.

0V, and VSEL is high, the output voltage is 1.2V. Extend battery life in the DSP system "S.