What about the lithium battery test solution based on ad8450/1 and ADP1972?

Energy consumption is a widespread problem across the globe, and many industries are working to address it by implementing safer, cleaner, more efficient and low-cost power solutions. The growing popularity of hybrid and electric cars, solar and wind power is the result of this trend. All these solutions have one thing in common: lithium-ion batteries. Due to the rapid growth in these areas, lithium ion batteries will play a more important role in energy conservation.

The manufacturing process for lithium-ion batteries is complex, including electrode production, stack construction and unit assembly. Electrical tests are then performed to assess battery capacity and performance. This is followed by electrical testing to assess the working capacity, or rating, of the battery. For these electrical tests in the manufacture of lithium ion batteries, high power, high efficiency and high precision testing equipment are required. Based on the ADI company AD8450/1 and ADP1972 solution is introduced.

System design considerations

Efficiency

Lithium-ion batteries in laptops, mobile phones and similar portable devices typically have a small capacity, typically several ampere-hours. But lithium-ion batteries, used in vehicles or to store energy, hold much more, often in the tens or hundreds of amperes. Linear test equipment used for small capacity battery, if also used for high capacity battery test, will consume a lot of power in the charging stage, resulting in low efficiency, and will bring serious thermal problems to the device hardware design. The ADIAD8450/1 and ADP1972 solutions are based on the PWM architecture and help solve this problem.

The ADIPWM architecture could also help send more battery power back to the grid or other test channels for charging. This is an environmentally friendly and efficient solution compared to linear architectures that discharge battery energy to resistive loads.

Precision

In order to obtain the accurate capacity of lithium ion battery, the current and voltage in charging and discharging modes need to be measured accurately. Combined with the precision ADC, DAC and other components in the system, ADI's ad8450/1 and ADP1972 solutions enable high-precision measurement and setting.

Low system cost

· higher switching frequencies support the use of smaller, less expensive power components such as inductance and capacitors

· energy recycling helps reduce operating costs

· with higher accuracy, ad8450/1 can reduce the cost of thermal management and simplify the design of control loop

· ad8450/1 adopts unique instrument amplifier design, which can shorten the calibration time in the manufacturing process by half and guarantee longer performance time

· integrated solutions allow for smaller system sizes and lower equipment and maintenance costs.

ADI solution

Note: the above signal chain represents the channel plate design from the dc bus to the battery. The technical requirements of the module may vary, but the products listed in the table below represent ADI solutions that meet some of the requirements.

1. Analog front end and controller AD8450/AD8451

2. Buck and boost PWM controller ADP1972

3. Micro controller ADuC7060/ADuC7061

4. Ad7173-8 / ad7175-2

5. DACAD5686R/AD5668 / AD5676R

6. Reference voltage source ADR3450/ADR4550

7.MOSFET driver ADuM7223

8. Power management ADP2441/ADP7102/ADM8829

9. Multiplexer ADG528F/ADG5408 / ADG658 / ADG1406

System operating principle

The figure above mainly contains two functions: one is to charge the battery, and the other is to discharge the battery, which is determined by the mode signal of ad8450/1 and ADP1972. Each function has two modes: constant current (CC) mode and constant pressure (CV) mode. Two DAC channels control CC and CV set points. The CC set point determines how much current there is in the loop under the CC mode of charging and discharging functions. The CV set point determines the battery potential of the loop from CC to CV, as well as the charging and discharging functions.

The precision analog front end and controller ad8450/1 measure the battery voltage using the internal differential amplifier PGDA, and measure the current on the battery using the internal instrument amplifier PGIA and the external shunt resistance (RS). It then compares the current and voltage to the DAC set point using an internal error amplifier and an external compensation network (used to determine whether the loop function is CC or CV). After this module, the output of the error amplifier goes into the PWM controller ADP1972 to determine the duty cycle of the MOSFET power level. And finally, the inductance and capacitors that make up the entire loop.The instructions in this section are for both charging and discharging functions, since ADP1972 is a step-down and step-up PWM controller.

In this scenario, the ADC takes readings of the loop voltage and current, but it is not part of the control loop. The sweep rate is independent of the performance of the control loop, so an ADC can measure the current and voltage across a large number of channels in a multichannel system. The same is true for DAC, so you can use a low-cost DAC to set up multiple channels. In addition, a single processor only needs to control the CV and CC set-points, working modes, and management functions, so it can interface with many channels.

The system performance

ADI produced the ADP1972 and AD8450 demo boards as shown below, which can be used to verify their efficiency and accuracy. For the asynchronous buck and boost power system, the dc bus input is 12V and the maximum charging/discharging current is 20A.

Efficiency: the efficiency of the demo board is approximately 90% at maximum rating, 20ACC mode (both charging and discharging functions), and 3.3v load. In order to achieve this value, the external diode, shunt resistance, inductance and MOSFET were optimized.

Accuracy: after calibration of the initial accuracy, the current accuracy includes temperature drift, linearity within the full current range (0A to 20A), short-term stability (noise), and CMRR within the full voltage range (0V to 3.6v). On the demo board verification as a result, the ADI typical current precision is less than 0.01% of the solution (25 ° C + 10 ° C). A similar analysis can be performed for the voltage accuracy, which is also below 0.01% as verified by this demo board.

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