Single lithium-ion battery protection of the chip design
Lithium-ion batteries to protect the design of its chip packaging is closely related to the structure, as shown in Figure 1 for the package in the internal lithium-ion batteries to protect the basic structure of the circuit. Under normal circumstances, charge and discharge control of CO-side control of the high potential for DO-side, N-discharge tube FET1 control and charge control in a turn-on control FET2, the circuit can be a work load to the battery discharge, can also be recharged laptop Battery-charging carried out; when the protection circuit is detected anomalies (charge-off, over and over-current discharge), so that the CO or DO low output in order to cut off the charge or discharge circuit to achieve protection.
In order to effectively use or discharge current charge current, FET1 and FET2 use on-resistance of a small power control. Their choice in addition to the principle of resistance is smaller, but also small and closed source and drain breakdown voltage should be able to withstand does not match the charger. In theory, FET1 and FET2 can control N can also be used P pipe. However, due to a single lithium-ion battery protection circuit of low-voltage power supply, in order to reduce the resistance, generally using N control. Figure 1 is a diode FET1 and FET2 parasitic diodes, the existence of the system they have in the state can discharge the battery charge, charge-off in the state can discharge the load.
Lithium-ion batteries to protect the chip applications requiring low current drive, high-precision detection of the characteristics of the other circuits due to the protection of the power supply is the Latitude D820 battery voltage, so the battery voltage changes, the protection circuit must be working properly, this article According to the connection as shown in Figure 1, the relationship between the design of a single low-power lithium-ion battery protection chip, the battery voltage can range of 1V-5.5V change.
System Design
Lithium-ion IBM batteries to protect the basic functions of the chip is the charge-off protection, over-discharge protection and over-current protection, over-current protection include the charge-discharge over-current protection and over-current protection. The following in order to protect the basic functions of the circuit as the starting point, his analysis of the system.
Anomaly detection
Lithium-ion battery protection circuit in order to achieve its basic functions, first of all need to detect anomalies. And the discharge had been charging the PA2522U-1BAS battery voltage detection is carried out partial pressure (sampling), compared with the voltage achieved; for over-current detection and protection of the chip will first of all in the process of charging and discharging current into power in the possession of FET1, FET2 on the Voltage, and then through the VM compared with the voltage, over-current discharge detection voltage is that, over-current charge is a negative voltage detection.
Signal interference filter
Usually in the lithium-ion battery protection circuit in the process of the work will interfere with the signal exists, the jamming signal, there are two main types: for a moment interference, which is the normal signal, in a very short period of time superimposed on a A larger signal. Another for interference fluctuations, which means the signal fluctuations. Figure 2 explains the process in order to charge the two types of interference, VCU for the charge-off voltage detection.
In order to prevent signal interference with the introduction of the protection circuit malfunction arising from the system point of view and adopt appropriate measures to reduce them.
Instant interference in the internal circuit protection circuit to add delay to filter out, that is, when the protection circuit is detected abnormal signals, delayed for some time and then shut down FET1 or FET2. According to the charge-off, over discharge, over-current lithium batteries on the extent of the harm to select a different time delay. In order to better protect the lithium F2019 battery , over-current discharge can be divided into three levels, namely an over-current protection, over-current protection and load-2 short-circuit protection, over-current of a longer delay, had flows more than 2 delay Over-current of a shorter delay, load and short circuit protection without delay immediately. Fluctuations in the interference in the internal circuit protection circuit to be coupled with slow to filter out.
Effective control of charge control tube to close
In the charging process, and FET2 source connected to the VM potential negative side, as a charge to protect the role, it must have been in charge and signal delay between the plus side CO-level conversion circuit, control logic Have a logic signal conversion, so that the CO-side potential is less than or equal to the potential end of the VM, in order to ensure effective FET2 off.
0V battery charge inhibiting function
Lithium-ion battery protection circuit can be carried out on the 0V battery charge, but also the realization of the prohibition on the 0V battery charge, the paper's design uses the latter, so that the function of the circuit protection against internal short-circuit the battery for charging. When the battery voltage of 0V battery voltage suppression VOINH (typical value of about 1V) or less when, FET2 potential of the gate was fixed for the VM's potential in order to prohibit the charge. When the battery voltage is equal to or higher than VOINH, can be recharged.
Other features
1) The charge-off in the state to protect the circuits required to prohibit the discharge over-current protection work. Because the batteries have been recharged after the load connected to the case, in the early discharge, the system is still in charge-off, this time bound to a large discharge current, over-current caused by the possibility of a lot; and over-current protection if the work on Turn-off will discharge circuit. In this way, once the batteries have been recharged, it may never be able to use;
2) play-off discharge protection, the protection of over-current protection circuit required to prohibit the charging function. When the battery discharge too, just connect the charger charging, the charge current will be great. At this point the Prohibition of charge over-current protection work, we can make sure the batteries have been recharged after discharge;
3) In order to reduce the charge current flowing through the internal parasitic diodes FET1 time, if a state of discharge have been connected to the charger and charging VM lower than the voltage over-current detection voltage, to lift-off delayed discharge.