As smart wireless devices and electric vehicles continue to evolve at breakneck speed, the demand for lithium batteries has surged dramatically. Manufacturers are ramping up production efficiency to meet these growing needs, especially with increasing pressure to reduce energy consumption and emissions. One of the key areas seeing innovation is the lithium battery formation process, which is increasingly incorporating energy feedback systems to promote energy savings and environmental protection.
If you're curious about how to conduct more precise component testing, TI's Field Applications Engineer (FAE) is here to guide you through an in-depth analysis! To ensure the accuracy of current and voltage measurements during battery charge and discharge cycles, the error tolerance must be incredibly tight—many customers aim for an error rate of 1 part in 10,000. This requires high precision in the amplifiers, ADCs, and DACs used in the circuitry.
In general, a comprehensive energy feedback lithium battery component tester typically consists of three distinct structural layers. Here's a breakdown:
1. **First Stage:** A bidirectional converter transforming 220V or 380V AC to 400-500V DC.
2. **Second Stage:** Another bidirectional converter stepping down from 400V DC to 12V DC.
3. **Third Stage:** A final bidirectional converter converting 12V DC to 5V DC.
The power level of each stage depends on the size of the battery being charged or discharged and the number of batteries involved. Utilizing TI’s C2000 TMS320F280XX series makes implementing the functions of the first two stages straightforward. These stages can even be combined to create a direct 220V AC to 12V DC converter, cutting costs further.
For the third-stage 12V DC to 5V DC bidirectional converter, most engineers traditionally rely on analog loop control schemes. However, let us explore a digital solution using the C2000 platform.
Above is TI’s analog loop control reference design, which is widely adopted due to its cost-effectiveness. The TL594 handles PWM control, while the LM5106 drives the half-bridge MOSFETs. Additionally, the LM5060 ensures battery reverse current protection. High-precision current and voltage acquisition and loop regulation are achieved primarily through the INA225 and OPA180. The INA225, a specialized current-sensing amplifier from TI, offers excellent temperature stability with an integrated external gain resistor. Its ability to automatically handle bidirectional current sensing simplifies circuit design significantly.
The OPA180 operates with self-stabilization and low temperature drift, making it ideal for PID regulation and constant current (CC)/constant voltage (CV) control. The ADS1248, a 24-bit delta-sigma ADC, collects charge/discharge voltages and currents but remains external to the loop control. Each ADS1248 can monitor four battery channels simultaneously, allowing flexibility in scaling based on external switches for optimal cost-efficiency.
The DAC80004, a 16-bit DAC, sets the charge and discharge voltage/current thresholds with minimal zero-point errors (<2mV), enabling lower current thresholds.
A critical aspect of this design lies in managing temperature drift. Amplifiers with low temperature drift properties are essential, and TI’s INA225 and INA240 excel in this regard, maintaining a gain error temperature drift below 2.5 ppm. The choice of sampling resistors also plays a crucial role; 20 ppm resistors are already quite advanced. During current sampling, resistors act as heat sources, potentially raising the temperature around the PCB, worsening thermal performance. Thus, careful PCB layout of the sampling resistors is vital.
To learn more about the PMP40182 reference design and its associated test data, check out the original article for detailed insights!
With TI's C2000 DSP gaining popularity, engineers are increasingly experimenting with using C2000 to manage 12V to 5V, 10A bidirectional battery charging/discharging controls. This approach achieves full digital bidirectional conversion from 220V AC to 5V DC.
Below is a schematic diagram illustrating the C2000’s 12V to 5V DC bidirectional DC-DC functionality. Leveraging TI’s latest TMS320F2837X, the CC and CV loops are controlled via C2000 software. The F2837X’s high-precision PWM (HRPWM) provides high-resolution DAC + PWM functionality without requiring an external DAC. Furthermore, its internal multi-channel 16-bit ADC eliminates the need for external ADCs while relying solely on external current sensing and amplification. By designing with the F2837X, the overall circuit complexity decreases, enhancing both reliability and temperature stability. Although a single F2837X might seem costly, it supports the charging and discharging of multiple batteries simultaneously, significantly lowering the per-channel cost.
Overall, TI offers an end-to-end solution tailored for modern battery-integrated test equipment, addressing technical challenges faced during product development and accelerating time-to-market.
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