The first chapter of the composition of the protection plate and the main role
This article mainly introduces the composition of lithium battery protection board, the main function and working principle of battery protection board. As well as the production of single lithium battery protection circuit application scope, electrical performance parameters, main materials, size specifications and other related items. All the items described in this specification standards can be used as quality inspection standards and basis.
2 Product application range
(1) liquid lithium-ion rechargeable batteries.
(2) Polymer lithium-ion rechargeable batteries.
1, the composition of the protection plate
The reason why lithium batteries (rechargeable) need protection is determined by their own characteristics. Because the material of the lithium battery itself determines that it can not be overcharged, overdischarged, overcurrent, short circuit, ultra-high temperature charging and discharging, so the lithium battery component of the lithium battery will always appear delicate protection plate and current fuse. The protection function of lithium battery is usually completed by the protection board and PT. The protection board consists of electronic circuits. It can accurately monitor the cell voltage and charge/discharge circuit current under the environment of -40℃ to +85℃. Control the current circuit on and off; PTC can prevent serious damage to the battery in a high temperature environment.
The protection board usually includes control IC, MOS switch, resistor, capacitor and auxiliary device NTC, ID memory, etc. Among them, the control IC controls the MOS switch to conduct under all normal conditions to enable the cell to communicate with the external circuit. When the battery voltage or circuit current exceeds the specified value, the MOS switch is immediately controlled to turn off (tens of milliseconds). Protects the battery.NTC stands for Negativetemperaturecoefficient, which means negative temperature coefficient. When the ambient temperature rises, its resistance decreases. The consumer or charging device responds in time and controls the internal interruption to stop charging and discharging. id memory is usually a single-wire interface memory. id is an abbreviation of identification, which means identification, storing information such as battery type, production date, etc. It can play the role of product traceability and application restrictions.
Second, the main role of the protection board
General requirements Control (IC) in -25 ℃ ~ 85 ℃ detection control battery voltage and charging and discharging circuit operating current, voltage, in all normal circumstances, C-MOS switching tube on to make the cell and protection board in a normal working state, when the cell voltage or circuit operating current exceeds the control IC when the circuit is preset, within 15-30ms (different control IC and C-MOS response time is different), CMOS shutdown, that is, to close the cell discharge or charging circuit, to ensure the safety of the user and the battery unit.
The working principle of Chapter 2 protection board
The IC is powered by the battery with a voltage between 2v-5v to ensure reliable operation.
1. Overcharge protection and overcharge protection recovery
When the battery is charged to a voltage exceeding the set value VC (4.25-4.35V, specific overcharge protection voltage depends on IC), VD1 flips to make Cout low, T1 ends and charging stops. When the battery voltage drops to VCR (3.8-4.1V, specific overcharge protection recovery voltage depends on IC), Cout becomes high and T1 conducts to continue charging, VCR must be less than a fixed value of VC to prevent frequent jumps
2、Over-discharge protection and over-discharge protection recovery
When the battery voltage drops to the set value VD (2.3-2.5V, the specific overcharge protection voltage depends on IC), VD2 flips over and after a short delay, Dout goes low, T2 cuts off and the discharge stops. When the battery is charging, the internal OR gate flips over and T2 conducts again to prepare for the next discharge.
3、Over-current and short-circuit protection
When the circuit charging and discharging circuit current exceeds the set value or short circuit, the short circuit detection circuit acts to turn off the MOS tube and cut off the current.
Chapter 3 protection board main components function introduction
R1: reference power supply resistor; it forms a voltage divider circuit with the internal resistance of the IC to control the internal overcharge and overdischarge? level inversion of the voltage comparator; general resistance value of 330Ω and 470Ω; when the package form (that is, the length and width of the standard components to indicate the size of the components, such as 0402 package logo, the length and width of the components are 1.0mm and 0.5mm) when the larger, the resistance value will be identified by a number. For example, the chip resistor on the digital mark 473 said its resistance value of 47000Ω or 47KΩ (the third bit indicates the number of bits after the first two plus 0). R2: overcurrent and short-circuit detection resistor; by detecting the voltage at the VM end to control the current of the protection board. Poor or damaged soldering will cause the battery to overcurrent and short circuit without protection. Typical resistor values are 1KΩ and 2KΩ. R3: ID identification resistor or NTC resistor (as described earlier) or both. In summary: The resistor is the black patch on the protection board. A multimeter can measure the resistance value. When the package is large, the resistance value will be expressed in numbers. Expression method as described above. Of course, the resistance value of the resistor is generally deviated, and each resistor has accuracy specifications. For example, a 10KΩ resistor specification of +/-5% accuracy means that the resistance value is in the range of 9.5KΩ-10.5KΩ. C1, C2: As the voltage at both ends of the capacitor cannot change suddenly, it plays the role of transient voltage regulation and filtering.
Summary: Capacitor is the yellow patch on the protection board. 0402 package has many types, 0603 package also has a few (1.6mm long, 0.8mm wide); resistance value is generally infinity or MΩ level; capacitor leakage will cause large self-consumption, no self-recovery in short circuit. fuse: common FUSE or PTC ( PositiveTemperatureCoefficient); to prevent unsafe high current and high temperature discharge, PTC has self-recovery function.
Summary: FUSE is generally a white patch on the protection board. the FUSE provided by LITTE will be marked on the FUSE character DT. character indicates the rated current that the FUSE can withstand. For example, the rated current of D is 0.25A, S is 4A, T is 5A, etc. At present, most of our products are FUSE with rated current of 5A, which is marked with "T" on the body.
U1: Control IC; all functions of the protection board are realized by the IC through monitoring the voltage difference between VDD-VSS and VM-VSS, and controlling C-MOS for switching action.
Cout: overcharge control terminal; the switching of MOS tube is controlled by the gate voltage of MOS tube T2.
Dout: Over-discharge, over-current and short-circuit control terminal; the switching of the MOS tube is controlled by the gate voltage of MOS tube T1.
VM: over-current and short-circuit protection voltage detection terminal; circuit over-current and short-circuit protection is achieved by detecting the voltage at the VM terminal (U(VM)=I*R(MOSFET)).
Summary: protection board in the IC is generally 6-pin package, distinguish the pin is: the first pin is marked near the black dot in the package body, and then counterclockwise rotation is the second, third, fourth, fifth and sixth pins; if the package body is not marked with a black dot, the first pin in the lower left of the package body characters, the other pins counterclockwise analogy) C-MOS: field-effect switching tubes; protection function is achieved by showing ; Continuous soldering, false soldering, false soldering, breakdown will cause the battery no protection, no display, low output voltage and other undesirable phenomena. Summary: CMOS in the protection board
Generally 8-pin package, consisting of two MOS tubes, equivalent to two switches, respectively, to control the overcharge protection and over-emission. Current and short-circuit protection; its pinout method is the same as the IC.
Protection board under normal conditions, Vdd is high, Vss, VM is low, Dout, Cout is high; when any of the parameters in Vdd, Vss, VM changes, the level of Dout or Cout will change. At this time, the MOSFET carries out the corresponding action (open and close the circuit), so as to achieve the protection and recovery function of the circuit.
Chapter 4 protection board main performance test methods
1. NTC resistance test.
Use a multimeter to directly measure the NTC resistance value, and then compare with the "temperature change and NTC resistance value".
2. Identification resistance test.
Use a multimeter to directly measure the identification resistance value, and then compare it with the "Protection Board Important Project Management Table".
3. Self-consumption test.
Adjust the constant current source to 3.7V/500mA; set the multimeter to uA, insert the meter pen into the uA jack, and then connect in series with the constant current source to the protection board B+ and B- as shown below: At this time, the reading for the multimeter is self-consumption of the protection board. If there is no reading, use tweezers or tin wire to connect B-, P-, and
\n to activate the circuit.
4、Short circuit protection test.
Connect the core to the protection board B+, B-, short the B-, P- with tweezers or tin wire, and then short the P+, P-; after the short circuit, use a multimeter to measure the voltage of the protection board
(as shown below); repeat the short circuit 3-5 times, at this time, the multimeter reading should be consistent with the core, the protection plate should not smoke, burst and other phenomena.
Connect the circuit, according to the important project management table to set the LEAA data, and then press the automatic button, and then press the button on the red meter pen to test. At this time, the lights of the RIYAN tester should light up one by one, indicating that the performance is OK. Press the display button to check the test data: "Chg" means overcharge protection voltage; "Dis" means over discharge protection voltage; "Ocur" means over current protection current.
Chapter 5 protection board common defects analysis
A. No display, low output voltage, no-load.
This defect is the first to exclude the bad battery (no battery voltage or low voltage), if the battery is bad, you should test the protection board self-consumption, see whether the protection board self-consumption is too large, the battery voltage is low. If the cell voltage is normal, it is because the whole circuit of the protection board is blocked (components are soldered, false welding, FUSE bad, PCB board internal circuit is blocked, over-hole is blocked, MOS, IC is blocked) damage, etc.). Specific analysis
Steps are as follows.
(1), the multimeter black pen connected to the negative terminal of the battery, the red pen connected to the FUSE and R1 resistor terminal, IC Vdd and Dout, Cout terminal, P + terminal (assuming that the cell voltage 3.8V), segmentation analysis, these test points should be 3.8V. If not, this part of the circuit has problems.
1, the voltage at both ends of the FUSE has changed: test whether the FUSE is on, if on, it means that the PCB board internal circuit is not on; if it does not open, FUS
There is a problem (bad incoming material, overcurrent damage (MOS or IC control failure), material problems (MOS or IC action before FUSE burned), then short the FUSE with a wire, and continue the analysis later.
\n2. There is a change in the voltage across the R1 resistor: test the resistance value of R1, if the resistance value is abnormal, it may be a false solder, the resistor itself is bad. If the resistance value is not abnormal, it may be a problem with the IC internal resistance.
3. there is a change in the voltage of the IC test terminal: the Vdd terminal is connected to the R1 resistor. the Dout and Cout terminals are abnormal because the IC is soldered or damaged.
4. If there is no change in the previous voltage, test the voltage between B- and P+ is abnormal because the positive through-hole of the protection board is blocked.
(B), multimeter red pen connected to the positive terminal of the core, after activating the MOS tube, the black pen is connected to the MOS tube 2, 3, 6, 7, P- terminal in turn.
1, if the MOS tube 2, 3, 6, 7 voltage changes, indicating that the MOS tube abnormal.
2, if the MOS tube voltage does not change, the P-terminal voltage is not normal, because the negative terminal of the protection board over the hole is blocked.
Second, short circuit without protection.
1. VM terminal resistance has a problem: a multimeter pen connected to the IC2 foot, a pen connected to the MOS foot connected to the VM terminal resistance. Confirm the resistance value
. Look at the resistance and IC, MOS pin no dummy solder.
2, IC and MOS abnormal: due to over-release protection and over-current short-circuit protection share a MOS tube, if the short-circuit abnormal is MOS problem, this board should not have over-release protection protection function.
3, the above is the normal case of defects, there may also be IC and MOS configuration is poor resulting in short-circuit abnormalities. For example, in the BK-901 that appeared early, the model number '312D' IC delay time is too long, resulting in MOS or other components have been damaged before the IC has taken the corresponding action control.
Note: The easiest and most direct way to determine if the IC or MOS is abnormal is to replace the suspect component.
Third, short-circuit protection without self-recovery.
1, the IC used in the design does not have a self-recovery function, such as G2J, G2Z, etc.
2, the short-circuit recovery time set by the instrument is too short, or the load is not unloaded during the short-circuit test. (Several megabytes of load).
3, leakage between P+ and P-, such as impurity rosin between the solder tray, impurity yellow glue or P+, P- capacitor breakdown, ICVdd to Vss breakdown (resistance value of only a few K to a few hundred K).
4, if the above are no problem, it may be IC bad. You can test the resistance between the IC pins.
Fourth, the internal resistance is large.
1, because the MOS internal resistance is relatively stable, there is a large internal resistance, the first suspect should be FUSE or PTC's relatively relatively. Easy to change the components.
2. If the resistance value of FUSE or PTC is normal, the over-hole resistance value between the P+, P- pad and the component surface can be detected according to the structure of the protection board. The value is larger.
3. If the above are no problems, we must suspect whether MOS is abnormal: first of all, determine whether there is a problem with welding; secondly, look at the thickness of the board (whether it is easy to bend), because bending may lead to bad pins are soldered will MOS tube under the microscope to observe whether the fracture; finally, use a multimeter to test the resistance value of MOS pins to see if there is a breakdown.
V. ID abnormalities.
1. false welding, broken or insufficient resistor material leads to ID resistor itself abnormal: you can re-weld the two ends of the resistor, if the ID is normal after re-welding, it means that the resistor is not properly welded. If it is bad, the resistor will be separated from it after re-soldering.
2. IDvia is not conducting: test both ends of the transistor with a multimeter.
3. Internal circuit has problems: You can scrape off the solder resist layer to see if the internal circuit is broken or shorted.
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