Microcircuits for protection of lithium accumulators. Reference data

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Modern lithium batteries and rechargeable batteries for powering cell phones and other portable electronic devices have high weight and size indicators and high energy intensity, but at the same time they are very sensitive to disturbances in charging and discharging modes. The consequences of such violations, often unintentional, can be quite severe - from a significant loss of energy consumption to a complete failure of the battery. The relative cost of lithium batteries and batteries is still high.

This forces a rather complex electronic device to be built into the batteries, which monitors the correct operation of the battery and does not allow it to go beyond the maximum permissible mode. The following describes the chips manufactured by ON Semiconductor, which are designed to perform exactly these functions. One of the NCP802 series will protect a single lithium battery, and the MC33351A will provide reliable operation of a battery of three such batteries. Familiarization with their features will help not only to properly operate the batteries, but also to restore performance after an unexpected "failure", often associated only with the operation of the built-in protection system.

Microcircuits of the NCP802 series

They are produced in several design modifications: NCP802SN1T1 - in a small-sized SOT-23-6 plastic package (Fig. 1), and NCP802SAN1T1 and NCP802SAN5T1 - in an even smaller SON-6 plastic package (Fig. 2).

(click to enlarge)

If the index G is added to the designation, the microcircuit is environmentally friendly (does not contain lead). On the NCP802 microcircuit case, only conditional marking is applied - the letters KN and the code for the date of manufacture. The full name with all indexes is indicated only in the accompanying documentation. The pinout of microcircuits is presented in Table. 1.

(click to enlarge)

A typical scheme for connecting the device to a protected lithium-ion battery is shown in fig. 3.

The R2C1 circuit is a power filter for the DA1 microcircuit. The resistance of the resistor R2 should not be more than 1 kOhm, since the voltage drop across it can unacceptably increase the thresholds for the operation of the protection unit. Resistors R1 and R2 limit the current through the chip if battery G1 is accidentally connected to a charger that develops too much voltage, or in the wrong polarity. In order not to exceed the power dissipation allowed for the microcircuit in these situations, the total resistance of these resistors must be at least 1 kOhm. However, if the resistance of the resistor R1 is more than 30 kOhm, the microcircuit may not enter the charging mode when a battery that is discharged to a level below the permissible level is connected to the charger.

Field-effect transistors VT1 and VT2 are connected in series in the charging / discharging circuit of the battery G1. In working condition, both of them are open, and the total resistance of their channels serves as a sensor of the current flowing in this circuit. If necessary, the current protection thresholds can be lowered by connecting in series between the drain terminals of the transistors an additional resistor not shown in the diagram.

If the transistor VT1 is closed, discharging the battery G1 to an external load is not possible. However, the charging current can freely flow through the protective diode built into the transistor, connected in the forward direction for this current. Similarly, the closed transistor VT2 prohibits charging, leaving the battery G1 possible to discharge. When both transistors are closed, the battery is completely disconnected from external circuits.

Overcharge protection

If the voltage at the Vcell output of the microcircuit increases, then at the moment when a certain threshold value U1 is exceeded, it sends a command to close the transistor VT2, setting a low voltage level at the CO output, equal to the voltage at the P- output, through the resistor R1 connected to the source of the transistor VT2.

The IC will return to high at the CO pin after the voltage applied to the Vcell pin decreases to a value slightly less than the threshold. The exit from the state with a low voltage level at the CO output will also occur after the load is connected to the battery, if the voltage drop caused by its current on the internal diode of the transistor VT2 - it is applied to the P- output - reaches the threshold level Uz (it is discussed below) or exceeds it .

The conditions for the transition of the microcircuit to the state of protection or return to its original state must be maintained for a long time before this transition occurs - a time delay is provided.

Over-discharge protection

When the voltage at the Vcell pin, decreasing, crosses the set threshold U2, a low voltage level will appear at the DO pin, which will lead to the closing of the transistor VT1 and the cessation of further discharge of the battery G1. The ability to charge remains. After the voltage at the Vcell pin exceeds the U2 threshold, the DO pin will go high again.

In the battery discharge inhibit state, the current drawn by the microcircuit drops sharply, as most of its internal nodes go into a passive state. A small increase in voltage at the P- pin, caused by connecting the battery to the charger, activates the microcircuit again

The timing diagrams of the voltage at various pins of the microcircuit and the current in the G1 battery circuit are shown in fig. 4 and 5. The first of them illustrates the operation of the battery protection unit from overcharging and exceeding the allowable charging current, and the second from overdischarging and exceeding the allowable discharge current.

(click to enlarge)

Protection against excess discharge current and short circuit of the battery terminals

This node operates when both transistors are open - VT1 and VT2. As soon as the voltage drop across them exceeds any of the threshold values ​​U3 or U5, the DO pin will go low, closing the transistor VT1. The delay in its closing when the discharge current is exceeded is approximately 12 ms, and when the battery terminals are closed, it is 0,4 ms. This is much less than the over-discharge protection node response delay.

As a result, the current protection unit operates first, preventing the microcircuit from switching to a passive mode, to exit from which it is necessary to connect the battery to the charger. To return to its original state after eliminating the short circuit or discharge current overload, it is enough that the voltage drop across the resistor Rs inside the microcircuit becomes less than the threshold. This resistor is connected between the Gnd (Common) and P- terminals when the current protection node has tripped and is disconnected from them in all other states.

Protection against exceeding the permissible charging current

When the charging current is greater than the allowable one (for example, the battery is connected to a “foreign” or faulty charger), the negative voltage at the P- pin is below the U4 threshold. If this situation has not changed for a certain time, the CO output will be set to a low level, which will lead to the closing of the field effect transistor VT2 and the charging will stop. To return to its original state, it is necessary to disconnect the battery from the charger and connect it to the load for a while.

Time Delay Management

As noted above, in order to change the state of the microcircuit, certain conditions must be in effect during the time intervals specified by the internal nodes of the microcircuit. If necessary, the delay can be disabled, after which the microcircuit will switch immediately after the occurrence of the corresponding condition (the duration of the operation of the nodes and the return to the operating mode is not regulated). To do this, it is enough to connect the DS output to the Vcell output. The normal state of the DS pin is not connected. An internal resistor is provided between it and the Gnd pin in the microcircuit.

Charging a heavily discharged battery

If the voltage between the Vcell and Gnd pins of the microcircuit is at least 1,5 V, its CO pin is high, the transistor VT2 is open. This allows you to start charging an almost completely discharged battery.

Main Specifications

• Supply voltage, V ...... 1,5 ... 4,5
• The minimum battery voltage at which you can start charging, V ...... 1,5
• The highest current consumed in the active mode, μA, at a supply voltage of 3,9 V and zero voltage at the P- pin ...... 6
• typical value......3
• The highest current consumed in passive mode, μA, at a supply voltage of 2 V ...... 0,1
• The highest value of the low-level voltage at the output of the charging transistor control CO, V, at a supply voltage of 4,5 V and an output current pulse of 50 μA ...... 0,5
• typical value......0,4
• The smallest value of the high-level voltage at the output of the CO controlling the charging transistor, V, with a supply voltage of 3,9 V and an output current pulse of -50 μA ...... 3,4
• typical value......3,7
• The highest value of the low-level voltage at the output DO of the discharge transistor control, V, at a supply voltage of 2 V and an output current pulse of 50 μA ...... 0,5
• typical value......0,2
• The smallest value of the high level voltage at the output DO of the discharge transistor control, V, at a supply voltage of 3,9 V and an output current pulse of -50 μA......3,4
• typical value......3,7

Overcharge Protection Assembly

• Threshold response voltage between the Vcell and Gnd terminals, V with a resistance of the resistor R2 (Fig. 3) of 330 Ohm and an ambient temperature within -5 ... +55 °С for NCP802SN1T1, NCP802SAN1T1 ..... 4,32 .. .4,38
• typical value......4,35
• NCP802SAN5T1 . . .4,245...4,305
• typical value .....4,275
• Threshold response voltage U,, V, with a resistance of resistor R2 330 Ohm and an ambient temperature of +25 °C for
• NCP802SN1T1, NCP802SAN1T1 .....4,325...4,375
• typical value......4,35
• NCP802SAN5T1......4,25...4,3
• typical value .....4,275
• Response delay t31, s, with increasing supply voltage (at the Vcell pin) from 3,6 to 4,4 V, for NCP802SN1T1, NCP802SAN1T1 ...0,175...0,325
• typical value......0,25
• NCP802SAN5T1......0,7...1,3
• typical value......1
• Return delay tB1 to operating mode, ms, with a supply voltage of 4 V and an increase in the voltage drop across the current sensor R1 from zero to 1 V......11...21
• typical value......16
• Overcharge protection unit
• Threshold operating voltage U2 (between Vcell and Gnd pins), V, for
• NCP802SN1T1, NCP802SAN1T1 .....2,34...2,46
• typical value......2,4
• NCP802SAN5T1 .....2,24...2,36
• typical value......2,3
• Operation delay t32, ms, when the supply voltage decreases from 3,6 to 2,2 V......14...26
• typical value......20
• Return delay tB2 to operating mode, ms, at a supply voltage of 3 V and a decrease in the voltage drop across the current sensor from 3 V to zero ..... 0,7 ... 1,7
• typical value......1,2
• Discharge overcurrent protection unit
• Threshold voltage U3 on the current sensor, V, for
• NCP802SN1T1, NCP802SAN1T1 .....0,18...0,22
• typical value......0,2
• NCP802SAN5T1 .....0,08...0,12
• typical value......0,1
• Response delay t33, ms, at a supply voltage of 3 V and an increase in the voltage drop across the current sensor from zero to 1 V for NCP802SN1T1, NCP802SAN1T1......8...16
• typical value......12
• NCP802SAN5T1......4..8
• typical value......6
• Return delay tB3 to operating mode, ms, at a supply voltage of 3 V and a decrease in the voltage drop across the current sensor from 3 V to zero ..... 0,7 ... 1,7
• typical value......1,2
• Charging Over Current Protection Unit
• Threshold voltage U4 on the current sensor, V, with a decrease in the voltage drop across it ..... -0,13 ... -0,07
• typical value ...... -0,1
• Response delay t34, ms, at a supply voltage of 3 V and a decrease in the voltage drop across the current sensor from zero to -1 V for NCP802SN1T1, NCP802SAN1T1......11...21
• typical value......16
• NCP802SAN5T1......5... 11
• typical value......8
• Return delay tB4 to operating mode, ms, at a supply voltage of 3 V and an increase in the voltage drop across the current sensor from -1 V to zero ...... 0,7 ... 1,7
• typical value......1,2

Node of protection against short circuit of external conclusions

• Threshold voltage U5 on the current sensor, V, at a supply voltage of 3 V. . .Upit - (1,4...1,8)
• typical value ..... Upit - 1,1
• Response delay t35, ms, at a supply voltage of 3 V and an increase in the voltage drop across the current sensor from zero to 3 V. .0,25...0,6 typical value......0,4
• Resistance between terminals P- and Gnd after the current protection unit trips, kOhm, at a supply voltage of 3,6 V and a voltage drop across the current sensor of 1 V ...... 15. ..45
• typical value......30
• Delay control node
• Voltage at the DS input, which cuts off delays, V......Upp+(-0,5...+0,3)
• Voltage at the unconnected DS input, V, at a supply voltage of 3,6 ... 4,4 V ...... 1,05 ... (Upi -1,1)
• Resistance of the internal resistor between the DS and Gnd pins, MΩ......0,5...2,5
• typical value......1,3
• Limit values
• Voltage, V, between Vcell and Gnd pins (supply voltage), as well as between DS and Gnd, DO and Gnd pins......-0,3...+12
• Voltage, V, between terminals P- and Gnd, as well as between CO and P-......Upit+(-28...+0,3)
• Maximum power dissipation, mW......150
• Working range of crystal temperature, °С......-40...+85
• Storage temperature, °С .. .-55...+125

With DS pin not connected, unless otherwise noted.

In addition to the above, the same company produces a series of MC33349N microcircuits, which differ from the NCP802SN1T1 mainly only in the values ​​of three parameters:

• Response threshold voltage U1, V (typical value) with 2 Ohm resistor R330 and ambient temperature +25 °С, for MC33349N-3R1, MC33349N-4R1......4,25
• MC33349N-7R1......4,35
• Threshold operating voltage U2, V (typical value) ...... 2,5
• Threshold voltage U3 on the current sensor, V (typical value), for
• MC33349N-3R1, MC33349N-7R1......0,2
• MC33349N-4R1......0,075

In the marking on the case of these microcircuits, instead of KN, an alphanumeric designation is applied: A1 - for MC33349N-3R1, A2 - MC33349N-4R1 and AO - MC33349N-7R1.

The manufacturer does not indicate the capacity of the capacitor C2.

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