3.7 volt battery 18650 charge protection integrated circuit
1. Characteristics of lithium-ion batteries
Compared with other batteries, lithium-ion batteries have the following
main advantages.
1. high voltage
The marked open circuit voltage is usually 3.6V, while the open circuit
voltage of nickel metal hydride and nickel cadmium batteries is 1.2V.
2. large capacity
High energy and high storage energy density are the core values of lithium
batteries. For the same output power, lithium-ion batteries are not only half
lighter than nickel-metal hydride batteries, but also 20% smaller in volume.
3. discharge rate
The charging speed of lithium-ion batteries is very fast, and it only takes
1 to 2 hours (h) to charge and reach the best state; at the same time, the
leakage of lithium-ion batteries is very small, even if it is left casually for
1 to 2 weeks before being picked up again When used out, it can still exert
power and work as usual; the self-discharge rate of lithium-ion batteries is as
low as <8%/month, which is much lower than the 30% of nickel-cadmium
batteries and 40% of nickel-metal hydride batteries.
4. Lithium-ion batteries do not have a "memory effect", so they can be
charged while not fully discharged without reducing their capacity. However, if
the lithium-ion battery is fully charged and continues to be charged
(overcharged), the battery will be damaged. Lithium-ion batteries are currently
widely used rechargeable batteries.
2. Charging characteristics of lithium-ion batteries
During the charging process of lithium-ion batteries, the voltage and
charging current of the battery will change with the charging time. The change
pattern is shown in Figure 1.
Charging a lithium-ion battery requires controlling its charging voltage,
limiting the charging current and accurately detecting the battery voltage. The
charging characteristics of lithium-ion batteries are completely different from
those of cadmium-nickel and nickel-metal hydride. Lithium-ion batteries can be
charged at any point during its discharge cycle, and can maintain its charge
very effectively. The retention time is more than twice as long as that of
nickel-metal hydride batteries. It is lightweight, and its weight is only 1/2 of
a cadmium-nickel battery of the same capacity. , the specific mass density is 4
times that of cadmium-nickel batteries. When the lithium-ion battery starts to
charge, the voltage rises slowly and the charging current gradually decreases.
When the battery voltage reaches about 4.2V, the battery voltage remains
basically unchanged and the charging current continues to decrease. The way to
determine whether the lithium-ion battery charging is completed is to detect it.
charging current, and ends charging when its charging current drops to a certain
value. For example, charging ends when the charging current of a lithium-ion
battery drops to 40mA (typically about 5% of the initial charging current). You
can also start a timer when it detects that the lithium-ion battery reaches 4.2V
and end it after a certain delay. Charge. At this time, the charging circuit
should have a battery voltage detection circuit with higher accuracy to prevent
overcharging of the lithium-ion battery. It should be noted that lithium-ion
batteries do not require trickle charging.
3. Main features of UCC3957
UCC3957 is a 3/4-cell lithium-ion battery pack charger protection control
integrated circuit using BiCMOS technology. It works with an external p-channel
MOSFET transistor to charge the battery pack to achieve two-level overcurrent
protection. If the first-level overcurrent threshold potential is reached, the
protection circuit will discharge the external capacitor according to the
protection time set by the user. If The first-level protection time is up, and
the battery overcharge and discharge faults have not been eliminated. The
external protection timing capacitor discharge MOSFET turns off at 17 times the
first-level protection time to implement the second-level protection, which is
very useful for capacitive loads. . The power consumption of UCC3957 in sleep
mode is only 3.5μA, the typical operating current is 30μA, and the DC operating
voltage range is 6.5∽20V. The charging overcurrent protection delay time can be
achieved by adjusting the parameters of external components. The advantage of
using an external p-channel MOSFET transistor is that it protects any cell from
overdischarge and overcharge, as well as protecting the battery pack and the
UCC3957 integrated circuit itself.
3.1 UCC3957 working principle block diagram and pin functions
The working principle block diagram of UCC3957 is shown in Figure 2.
Figure 2 UCC3957 working principle block diagram
As can be seen from Figure 2, the working status of UCC3957 can be selected
using the internal working status selector of UCC3957. When working in the
continuous working status, each lithium-ion battery can be protected from
overcharge and overdischarge. The over-current controller is used to protect the
battery pack from generating excessive discharge current and damaging the
battery pack.
In order to match the lithium batteries produced by different
manufacturers, the UCC3957 series integrated circuits have 4 different
overvoltage protection thresholds as shown in Table 1.
Table 1 UCC3957-X overvoltage protection threshold value (V)
The pin diagram of UCC3957 is shown in Figure 3.
Figure 3 Pin diagram of UCC3957
The functions of each pin of UCC3957 are as follows:
Pin 1VDD: This pin is the power supply input pin of UCC3957. The input
voltage range is 6.5~20V and is connected to the high potential end of the
battery pack.
Pin 2CLCNT: This pin is the pin that sets the UCC3957 to work in the
charging state of three or four cells.
Pin 3WU: This pin is when the UCC3957 is in the dormant working state.
Adding a signal to this pin can wake up the UCC3957 and enter the normal working
state. This pin should be connected to the drain of the N-channel level shift
MOSFET transistor.
Pin 4AN1: This pin is connected to the negative electrode of the highest
potential battery cell 1 and the positive electrode of the second battery
cell.
Pin 5AN2: This pin is the pin connecting the negative electrode of the
second battery with the highest potential and the positive electrode of the
third battery.
Pin 6AN3: This pin is the pin connecting the negative electrode of the 3rd
battery with the lowest potential and the positive electrode of the 4th battery.
When there are only 3 batteries, it is connected to the low potential end of the
battery pack and the AN4 pin.
Pins 7 and 11 AN4: This pin is connected to the low potential end of the
battery pack and to the high potential end of the current sensing resistor.
Pin 8BATLO: This pin is connected to the negative potential end of the
battery pack and at the same time connected to the low potential end of the
current detection resistor.
Pin 9CHGEN: This pin is the charging enable pin. When this pin is high
level, the battery pack starts charging.
Pin 10CDLY1: This pin is the delay time control pin for short circuit
protection. The value of the capacitor connected between this pin and the AN4
pin determines the overcurrent time. When the overcurrent occurs, it controls
the turn-off time of the discharge MOSFET transistor. The capacitor The value
also determines the hiccup over-current protection time.
Pin 12CHG: This pin is connected to an external controllable N-channel
MOSFET transistor, and the external N-channel MOSFET transistor can be used to
drive an external p-channel MOSFET. If any battery voltage is higher than If the
overvoltage protection threshold potential is reached, this pin will be set to a
low potential relative to the AN4 pin; only when the voltage of all single-cell
batteries being charged is lower than the threshold potential, this pin will be
set to a high potential.
Pin 13DCHG: This pin is used to prevent battery over-discharge. If the
working status detector inside UCC3957 determines that any battery is in an
under-voltage state, the pin DCHG is set to a high potential to turn off the
external discharge p-channel MOSFET transistor. However, when the voltage of all
batteries is higher than the minimum threshold potential, the pin DCHG is set to
low potential.
Pin 14CDLY2: Connect a capacitor between this pin and the AN4 pin to extend
the protection setting time of the second-level overcurrent protection.
Pin 15AVDD: This pin is connected to the AN4 pin through a 0.1μF capacitor.
The normal operating voltage is 7.3V.
Pin 16DVDD: This pin is connected to the AN4 pin through a 0.1μF capacitor,
which is the power supply pin for the internal digital circuit. The normal
operating voltage is 7.3V.
4. Working principle and typical application circuit of UCC3957
4.1 Working principle of UCC3957
UCC3957 can provide comprehensive protection functions for 3-cell or 4-cell
lithium battery packs to prevent battery overcharge, over-discharge,
over-current charge and discharge, etc. It samples the voltage of each cell in
the battery pack and compares it with the internal precision reference The
voltage is compared, and when any battery is in an overvoltage or undervoltage
state, the UCC3957 will take appropriate measures to prevent the battery from
further charging or discharging. UCC3957 is externally connected with two
independent p-channel MOSFET transistors to control the charging and discharging
current of the battery respectively.
The following takes Figure 4 as an example to introduce the characteristics
of the 4-cell lithium battery charging protection circuit using UCC3957.
1. Battery pack connection
Pay attention to the order when connecting the battery pack to the UCC3957.
The low potential end of the battery pack is connected to pin 7AN4, the high
potential end is connected to pin VDD, and the connection points of every two
batteries are connected to pins 4AN1, 5AN2, and 6AN3 in the corresponding
order.
2. Choose 3 or 4 battery charging working status
When the battery pack is 3 cells, pin 2CLCNT should be connected to pin
16DVDD, and pin 6AN3 and pin 7AN4 should be connected together. When the battery
pack is 4 cells, pin 2CLCNT should be connected to ground (that is, connected to
pin Pin 7AN4), AN3 pin is connected to the positive terminal of the bottom
battery of the battery pack.
3. Under voltage protection
When it is detected that any battery is in an over-discharge state (lower
than the under-voltage threshold potential), the status detector turns off two
MOSFET transistors at the same time, causing the UCC3957 to enter the sleep
mode. At this time, the power consumption of the UCC3957 is only 3.5μA. , only
when the voltage of pin 3WU rises to 1VDD, UCC3957 exits the sleep mode.
4. Charging batteries
When the charger is connected to the charging power supply, as long as the
voltage of pin 9CHGEN is pulled to 16DVDD, the charging FET transistor VT1 is
turned on and the battery pack is charged. But if pin 9CHGEN is left open or
connected to pin 7AN4, the charging FET transistor VT1 is turned off. During
charging, if the UCC3957 is in the sleep mode, the discharge FET transistor VT2
is still turned off, and the charging current flows through the body diode of
the discharge FET transistor VT2; until the voltage of each battery is higher
than the undervoltage threshold voltage, the discharge FET transistor VT2
conduction. During sleep operation, the charging FET transistor VT1 is in a
periodic turn-on and turn-off mode, with a turn-on time of 7ms and a turn-off
time of 10ms.
5. Protection against abnormal battery connection
UCC3957 has a protection function in case of abnormal battery connection in
the charged battery box. If the pins 4AN1, 5AN2 or 6AN3 connected to the battery
are not connected properly or disconnected, UCC3957 can detect and prevent the
battery pack from overcharging.
6. Overvoltage protection and intelligent discharge characteristics
If the charging voltage of a certain battery exceeds the normal overcharge
threshold potential, the charging FET transistor VT1 is turned off to prevent
the battery from overcharging. Shutdown remains until the battery voltage drops
to the overcharge threshold level. In most protection circuit designs, the
charging FET transistor VT1 is always fully protected within this overvoltage
protection band (between normal value ∽ overcharge threshold, or conversely,
between overcharge threshold ∽ normal value). In the off working state, the
discharge current must pass through the body diode of the charging FET
transistor VT1. The voltage drop of the diode is as high as 1V, which causes
great power consumption in the charging FET transistor VT1 and consumes precious
battery power.
UCC3957 has a unique intelligent discharge characteristic, which can make
the charging FET transistor VT1 conductive to the discharge current (only for
discharge) while still being within the over-voltage hysteresis range. This
greatly reduces the power dissipated in charging FET transistor VT1. This
measure is accomplished by sampling the voltage drop flowing through the current
sensing resistor RSENES. If this voltage drop exceeds 15mV (0.025Ω current
sensing resistor corresponds to a discharge current of 0.6A), the charging FET
transistor VT1 is turned on again. In this example, if the body diode voltage
drop of a 20mW FET transistor is 1V, corresponding to a 1A load, the power
consumption of VT1 is reduced from 1W to 0.02W.
7. Over current protection
UCC3957 uses a secondary overcurrent protection mode to protect the battery
pack from overcharging current and battery pack short circuit. When the voltage
drop on the current detection resistor RSENSE (connected between pin AN4 and pin
BATLO) exceeds a certain threshold potential, The over-current protection enters
the hiccup protection working mode. In this operating mode, the discharge FET
transistor VT2 is turned off and on periodically until the fault is eliminated.
Once the fault is eliminated, the UCC3957 automatically resumes normal
operation.
In order to adapt to large capacitive loads, UCC3957 has two over-current
threshold voltages, and different delay times can be set corresponding to each
threshold voltage. This secondary overcurrent protection provides fast response
to short circuits while allowing the battery pack to withstand certain surge
currents. This can prevent unnecessary overcurrent protection actions caused by
large filter capacitance.
The first-level overcurrent protection threshold potential is 150mV,
corresponding to a 0.025Ω current detection resistor, and the overcurrent
threshold is 6A. If the peak discharge current lasts longer than the time set by
this value (set by the capacitor connected between CDLY1 and ground), UCC3957
enters the hiccup protection operating mode. The duty cycle of the hiccup
protection working mode is about 6%, that is, the off time is about 17 times the
on time.
The second-level overcurrent threshold potential is 375mV, corresponding to
a 0.025Ω current detection resistor, and the overcurrent threshold is 15A. If
the peak discharge current exceeds the time set by this potential value (set by
the capacitor connected between CCDLY2 and ground), UCC3957 enters the hiccup
protection working mode, and the duty cycle is generally less than 1%. The off
time tOFF is still determined by the capacitor connected between CCDLY1 and
ground. This technology greatly reduces the power consumption on the FET
transistor VT2 during a short circuit, thereby reducing the requirements for the
use of the FET transistor VT2.
When CDLY1=0.022μF, the on-time tON corresponding to the first-level
overcurrent (when the current is greater than 6A and less than 15A) is
approximately 10ms, the off-time tOFF is approximately 160ms, and the duty cycle
is 5.9%; when If CDLY2 is not used when the current exceeds 15A, the duty cycle
of the second-level overcurrent protection is 0.1%; if CDLY2 is 22pF, the
corresponding conduction time is 800μs and the duty cycle is 0.5%.
4.2 Typical application circuit of UCC3957
A typical protection circuit for a 4-cell battery pack using UCC3957 is
shown in Figure 4.
Figure 44 Typical protection circuit for lithium battery charging
circuit
In Figure 4, VR1 and R2 are used to protect the charging FET transistor VT1
when the charger's open circuit charging voltage is too high. In this
application circuit, when short-circuitedWhen the discharge FET transistor VT2
is turned off, due to the distributed inductance of the battery pack output, a
negative sudden change in voltage will occur; this negative sudden change will
exceed the withstand voltage value of the discharge FET transistor VT2, and this
negative sudden change will also damage the UCC3597. VD1 in Figure 4 clamps this
negative mutation to protect the discharge FET transistor VT2, C5 should be
placed directly on the top and bottom of the battery pack.
Because when the discharge overcurrent protection occurs, the negative
voltage overcharge generated by the discharge FET transistor VT2 is related to
the size and the rise and fall time of the turn-on and turn-off drive pulses of
the discharge FET transistor VT2. Therefore, R3, C5, and R4 are used to control
the size in Figure 4.
Read recommendations:
Coin Battery LR 43
Prospects for the development of lithium water batteries.LR6 alkaline battery
3.2v 60ah lifepo4 battery.What is the concept of 18650 batteries?
cabinet type energy storage battery direct sales
LR1130 battery