BTS660 and its application in battery intelligent detection and charging device

Rechargeable batteries are widely used in industrial and agricultural production, national defense science and technology and other fields, and the detection and charging of rechargeable batteries are problems that must be solved during the use of rechargeable batteries. The battery intelligent detection and charging device is a set of equipment specially developed for the detection and charging of rechargeable batteries. In the design process, the high-precision high-current switch of BTS660 is fully utilized to realize the current and voltage conversion of rechargeable batteries during the detection and charging process, thereby realizing various functions.

1 BTS660 Performance Features

BTS660 is a high-precision, high-current power switch produced by Infineon Technologies AG. It is a power MOSFET that can achieve reverse battery protection through self-opening function. It can be used to replace relays, fuses and discrete circuits in electric machinery; it can be used as a grounded load and can reach a DC 48 V power switch; it is suitable for devices such as lamps and generators that load high instantaneous currents, as well as various types of capacitive and inductive loads.

The main features of BTS660 are as follows: overload protection; current limiting, load current can reach up to 44 A, short-circuit current limit is 90 A; short-circuit protection; overheat protection, operating temperature range -40 ~ +150 ℃, storage temperature range is -55 ~ +150 ℃; operating voltage is 5.0 ~ 58 V, overvoltage protection is 70 V; negative voltage output lock; fast disconnection of inductive loads; low resistance reverse current operation; diagnostic feedback of load current information; current open circuit load detection; power supply power-off protection; electrostatic discharge protection.

2 BTS660 internal structure and pin description

2.1 Internal structure

BTs660 is an N-channel vertical power field effect transistor with a charge pump. It has the ability of current control input and current feedback diagnosis for load current, and has multiple protection functions integrated inside. Figure 1 is the internal functional structure block diagram of BTS660, which consists of a voltage source, a voltage sensor, a temperature sensor, a charge pump standard conversion regulator, and overvoltage, current limiting, and overload protection.

BTS660 is mainly composed of the following parts: 1) Input circuit, i.e. electrostatic discharge protection. When the current IIN flowing through pin 3 is 0, the power switch is turned on and the device starts to work; when IIN is not 0, the switch is closed and the device stops working. 2) Overvoltage protection circuit. When the voltage sensor detects that the voltage exceeds 70 V, the logic control circuit will disconnect the voltage source voltage. 3) Charge pump standard conversion regulator; 4) Output voltage detection circuit. Detect the output voltage to prevent the voltage from being too high or too low; 5) Overload limit circuit. Detect the load size. When the load is too large, limit the load to protect it. 6) Current judgment and protection circuit. Detect the current size and protect it when it is overcurrent.

2.2 Pin Description

BTS660 adopts T0220-7SMD package, with a total of 7 pins. The functions of each pin are as follows: 1) Pins 1, 2, 6, 7: load output, these pins must be short-circuited, especially in high current applications; 2) Pin 3: input end, when this pin is at a low level, the power switch is turned on; 3) Pin 4: power input end, under normal circumstances, the operating voltage is 5.0~58 V: 4) Pin 5: diagnostic feedback of the load current flow ratio.

3 Application of BTS660 in intelligent battery detection and charging device

According to the characteristics of the detection object - military rechargeable batteries, the battery intelligent detection and charging device can mainly complete functions such as battery capacity detection, fast charging, normal charging, battery discharge, and battery repair. In the system design process, the current variation range through the device is required to be relatively large, and because the reverse pulse charging method is used to realize battery charging and discharging, a charge and discharge conversion must be realized within a pulse cycle, so the control device is very demanding. At the beginning of the design, other devices were selected for control, but the effect was poor and it was easy to burn out. After repeated demonstrations and reference to materials, it was finally determined to use BTS660 as the charge and discharge controller.

According to the functions and characteristics of BTS660, when designing the battery intelligent detection and charging device, BTS660 is used to realize the control of battery charging and discharging. Its application design circuit diagram is shown in Figure 2. Two BTS660s (U1 and U2) are used in Figure 2, where U1 controls the current in the charging process and U2 controls the current in the discharging process. The output of U1 is used as the input of U2, so that the device cascade can be realized, and the INPUT terminal is connected to the constant current source. Pin 4 of BTS660 is connected to the power supply; pins 1, 2, 6, and 7 are short-circuited as outputs, and the output terminal is connected to the load. The load is a rechargeable battery during charging and a discharge resistor during discharging; pin 3 is the input, and the input terminal is connected to 4N25 to achieve photoelectric isolation; a discharge resistor is connected between pin 5 and the ground, and the output of this pin is the charging and discharging sampling current, which is connected to the microcontroller through the voltage sampling circuit.

In the charge and discharge loop control, the charge and discharge loops are each controlled by one BTS660. During charging, when pin 3 of U1 is low, U1 is turned on, and the constant current source and the rechargeable battery form a charging loop. At this time, the current (0UT1) output by pin 5 of U1 sends data to the microcontroller interface through the charging current sampling circuit, and the microcontroller issues instructions to control the battery charging. 0UT3 provides the system with battery terminal voltage sampling; during discharging, when pin 3 of U2 is low, U2 is turned on, and the rechargeable battery and the high current discharge load form a loop. At this time, the current (0UT2) output by pin 5 of U2 sends data to the microcontroller interface through the discharge current sampling circuit, and the microcontroller sends instructions to control the battery discharge.

During the charging and discharging process, pin 3 of BTS660 controls its conduction (ground conduction), and pin 5 reflects the size of the device output current Is, which can be calculated by formula (1):

Where Is is the feedback current output from pin 5, IL is the current output from BTS660 to the battery, and Kilis value is related to temperature and IL.

When detecting current, connect a resistor in series from pin 5 of BTS660 to ground, and its resistance is:

In the formula, IL(M) is the maximum current output by BTS660 during normal operation, and Vbb is its input voltage. After calculation, a l kΩ resistor is selected.

Experiments have proven that the application of BTS660 in battery intelligent detection and charging devices can fully meet the design requirements. The battery detection and charging device has also been successfully used in production, running stably and with good results.

4 Conclusion

BTS660 is a high-precision, high-current power switch with powerful functions and low price, which is particularly suitable for various battery protection and large charger design. The battery intelligent detection and charging device designed with BTS660 as the core control device has been mass-produced and successfully applied in a certain military field. The system runs stably and has good results.