Smart battery charging built by the hottest microp

Smart battery charger scheme built by microprocessor and dc/dc controller

with the increasingly common use of lithium-ion chemical batteries in the design of various electronic products, innovative solutions for charging these batteries become more and more necessary. To maximize system flexibility, we can use microprocessors to control all aspects of battery charging, including unique charging algorithms designed to improve charging rate and battery life. This method can also allow higher voltage battery packs to be implemented

this paper will introduce how to use a microprocessor to control the power stage board of a wide input voltage dc/dc controller. This solution can support input voltages up to 55v; Battery charging voltage in the range of 5V to 51V; And an output current of up to 10A in most cases. The hardware and software discussed in this article are developed by Ti application staff and tested by them, in order to enable customers to quickly manufacture solution prototypes

for ease of development, we split the battery charger into two separate boards: the microprocessor controller board and the dc/dc-converter power stage board (see Figure 1). The positive and negative battery terminals are connected to the power stage board, and the system management bus (SMBus) communication line is connected to the microprocessor board. The smart battery sends the charging voltage and current information we want to the microprocessor, and then sends two pulse width modulation (PWM) signals to the dc/dc-converter power stage board to set the actual output voltage and current

Figure 1: advanced system structure diagram of wide input voltage intelligent battery charger

in order to use standard wide input voltage dc/dc converter, the power stage board is designed with a special feedback circuit (see Figure 2) to correctly control battery charging. The charging sequence followed by the microprocessor is to limit the charging current until the battery voltage approaches its specified maximum voltage. When the maximum voltage is reached, the charging voltage remains constant, so that the charging current gradually decreases until the battery is considered to be fully charged. At this time, the PWM output signal is turned off

Figure 2: constant current/voltage feedback circuit for correctly charging the battery

initial current limit charging rate has two current levels. When the battery is over discharged, a very low charging rate will be used until the battery voltage reaches a safe enough level to accept the standard charging rate

in the feedback circuit shown in Figure 2, u3:b compares the PWM current reference voltage (i_pwm1) with the measured current (isns1) supplied to the battery. If the PWM reference voltage is higher than the measured current, the amplifier output is high. If the reference voltage is low, the amplifier output is low

a resistance voltage divider (R30 and R34) is used to measure the output voltage of vbatt1 input terminal of u3:a. We compare this voltage with the PWM output reference voltage (v_pwm1). If the reference voltage is higher, the amplifier output is high. If the reference voltage is lower, the amplifier output express packaging material will not be degraded to low for 100 years. The maximum output voltage can be expressed by the following equation:

D1 diode combines two amplifier outputs with a logic or. The lowest voltage is supplied to the inverting amplifier (u3:d), which makes the polarity of the error signal correct when using the dc/dc controller (here is ti's tps40170). The basic working principle is: the controller attempts to send a set current; At the same time, if the load can accept the current, the controller will adjust to the current level. If the load does not accept all the current, the voltage begins to rise and finally reaches Vout (max). When this happens, the voltage loop takes over and adjusts the output voltage informed by Professor Guo

if you want to improve the security of the solution, the power stage board should also have a protection circuit with overvoltage status (up to 100V) and reverse voltage connection (its positive and negative poles are exchanged). Figure 3 shows this circuit

Figure 3: overvoltage and reverse pole protection circuit

when the input voltage is reversed, the reverse voltage protection is provided by MOSFETs Q7 and Q9 and D2. This will not allow negative voltage to be applied to the system. The output result function of input overvoltage protection experiment can be set arbitrarily: the maximum force value and elongation are provided by MOSFET Q8 and Q10. Zener diode D4 sets the voltage at which the circuit begins to clamp. Once the zener voltage is exceeded, the gate source voltage of the FET begins to drop. This enables the FET to work in the active area and allows the microprocessor to continue to be powered. At the same time, the dc/dc converter is turned off and the signals sd1 and SD2 are pulled to ground

software implementation is as important as hardware implementation. A brief software flowchart is shown in Figure 4. The microprocessor asks the battery through SMBus for the desired charging voltage and current. After confirming these values, it sets two PWM outputs to adjust the output voltage and current reaching the battery. If at any time, the battery issues a charging warning, the PWM output is turned off. In addition, once the charge state of the battery reaches 100% or the set full charge position, the PWM output is turned off

Figure 4: brief description of software flow chart

safety is the most important issue during battery charging. All solutions should have several layers of protection. The first protective layer is the smart battery itself with internal protection MOSFET, which will cause the equipment to rust. During charging, the microprocessor should communicate with the battery regularly (preferably every 2 seconds) to monitor all safety signs in the "battery status" register. Some flag bits that require response include overcharge warning (OCA), end of charge warning (TCA), ultra high temperature warning (OTA), and full charge (FC) status. The on-board analog-to-digital converter of the microprocessor can be used as a secondary check for overvoltage or overcurrent events

conclusion

by using a microprocessor with a wide input voltage dc/dc controller, we can design a fully programmable, wide input voltage battery charger. This paper introduces a solution, which uses ti's low-power msp430f5510 microprocessor and tps40170 dc/dc controller to build a structure that can support up to 55v input voltage. This paper describes a special feedback network developed by Ti application staff to implement correct battery charging. In addition, we also discuss a novel solution for overvoltage protection and reverse voltage protection