CXLB73308 is an efficient buck-boost charging management chip that supports 1 to 4 strings of lithium-ion batteries. It adopts Buck-Boost topology and integrates low RDS(on) MOSFET, which significantly reduces the number of peripheral components and improves system efficiency. Its input voltage range is 4.2V-21V, and the maximum output power can reach 25W. It is suitable for various fast charging adapters and USB PD power supplies.
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[ CXLB73308 ]"
CXLB73308 buck-boost charging chip: efficient and flexible 25W multi-string battery charging solution
With the popularization of fast charging technology and the continuous expansion of lithium battery application scenarios, the market demand for efficient and integrated charging management chips is increasing. As a buck-boost charging converter designed for modern DC fast charging scenarios, CXLB73308 has become an ideal choice for mobile power, industrial equipment and automotive systems with its high integration, wide voltage range and flexible configuration capabilities. This article will comprehensively analyze the technical characteristics, working principles and design practices of the CXLB73308 to help engineers build high-performance charging systems.
1. chip overview and core advantages
CXLB73308 is an efficient buck-boost charging management chip that supports 1 to 4 strings of lithium-ion batteries. It adopts Buck-Boost topology and integrates low RDS(on) MOSFET, which significantly reduces the number of peripheral components and improves system efficiency. Its input voltage range is 4.2V-21V, and the maximum output power can reach 25W. It is suitable for various fast charging adapters and USB PD power supplies.
Key features include:
· Wide input voltage range: 4.2V-21V, suitable for various fast charging protocols;
· Support 1~4 strings of lithium batteries, charging voltage and current can be flexibly set through external resistors;
· Integrated high efficiency MOSFET, optimal system efficiency;
· 450kHz switching frequency, taking into account the efficiency and component volume;
· Quiescent current as low as 5μA, suitable for normal power supply equipment;
· Built-in multiple protections: short circuit, over temperature, battery low temperature/over temperature protection;
· Small QFN3x4-15 package for compact design.
2. system structure and electrical performance
The CXLB73308 uses a single-inductor four-switch Buck-Boost architecture to support stable operation when the input voltage is higher than, lower than, or equal to the battery voltage. Its internal integrated current mode control loop enables smooth mode switching and fast dynamic response.
2.1. KEY ELECTRICAL PARAMETERS:
· Switching frequency: 450kHz (typical);
· On-resistance: the typical value of RDS(on) of each switch is 28mΩ;
· Constant voltage accuracy: BATFB feedback voltage accuracy of ± 1%;
· Charging current range: support several mA to 3A adjustable;
· Working temperature:-40 ℃ to 125 ℃.
2.2. Absolute Maximum
VIN, BAT, SW1, SW2 Pins……………………………………………………………………………………………………-0.3V to 24V
BST1-SW1, BST2-SW2…………………………………………………………………………………… -0.3V to 6.5V
All other pins……………………………………………………………………………………… -0.3V to 6.5V
Working temperature 2)3)…………………………………………………………………………………………150°C
Welding temperature………………………………………………………………………………………………260°C
Storage temperature……………………………………………………………………………………………… -65°C to 150°C
Electrostatic Discharge Sensitivity (Mannequin)……………………………………………………………± 2k
2.3. Recommended operating conditions
Input voltage VIN ……………………………………………………………………………………… 4.2V -21V
VBAT……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
Operating Temperature Range (TJ)………………………………………………………………………………………………………………………………………………… 40°C -( 125°C)
2.4. Thermal performance
QFN3X4-15……………………………………………………………………………………… 48… 11°C/W
Note:
1. Exceeding these ratings may damage the chip. These stress ratings do not imply any other indication of the chip under the recommended operating conditions.
condition of functional operation.
2. Continuous operation at the specified absolute maximum operating junction temperature may damage the chip.
3. There is no guarantee that the chip will work outside its operating conditions.
4. Measured on JESD51-7, 4-layer PCB.
3. charging process and mode control
The CXLB73308 adopts three-stage charging management:Current elimination charge (Trickle Charge),Constant current charging (Constant Current)withConstant voltage charging (Constant Voltage)Ensure that the battery charging process is safe and complete.
· current elimination charging: When the battery voltage is lower than VTRI, activate the battery with a small current (typically 10% ~ 30% of ICC);
· constant current charging: After the battery voltage is normal, charge quickly with the set current;
· constant voltage charging: When the battery is close to full power, it turns to constant voltage mode, and the current gradually decreases until the charging is terminated.
In addition, the chip supportsInput adaptive function, When the adapter power is insufficient, the charging current is automatically limited to avoid the input voltage drop.
3.1. Function description
The CXLB73308 is a single-chip buck-boost charger that can operate over a wide input voltage range of 4.2V to 21V. Full charging voltage and charging power
The flow can be regulated by an external resistor. The low RDSON N-channel power switch reduces solution complexity and improves efficiency.
The DC-DC converter uses a proprietary single-inductor current-mode control to ensure a smooth transition between buck and boost switching, with better dynamics
Response and cycle-by-cycle current protection. The compensation is done inside the chip. The CXLB73308 operates in PFM mode at light loads. In PFM mode, the switch
The frequency is continuously controlled in proportion to the load current, that is, when the load current drops, the switching frequency is reduced to improve the light by reducing the switching loss
power efficiency under load, thereby minimizing the circuit.
If the voltage of the CE pin is in the normal range, the CXLB73308 can work in charging mode. In charging mode, if the VIN voltage is lower
The battery voltage is the boost charger. When the VIN voltage is higher than the battery voltage, it is a buck charger.
3.1.1 Charging mode
In charge mode, the CXLB73308 regulates the battery current based on the input voltage and the battery voltage. It performs three-stage charging on the battery: trickle charging, constant charging
Current charging, constant voltage charging. Figure 1(a) is a typical charging profile. Figure 1 (B) is a charging profile with input voltage limitation. When entering
When the voltage is limited, the system reduces the charging current.
CV charging
When the battery voltage is equal to VCVThe device adjusts the battery voltage and reduces the charging current, thereby automatically reducing it. Users can select 2 series of electricity
pool or via BATFB pin to VCVAdjust. Connect BATFB to GND to select 2 strings of batteries. VCV You can also connect to the BATFB
The resistor divider is adjusted. We recommend the use of resistors with an accuracy of 1 ‰ to achieve the accuracy of the full power voltage. Full electric voltage distribution
set as shown in Figure 3. We recommend equal to or less than 4 strings of cells in series applications. When the number of batteries in series is greater than 3, the BAT pin needs to be
To add an electrolytic capacitor to suppress the spike voltage.
Termination of charging work
If the battery voltage is higher than VFULL, And the charging current is less than TFULLCharge termination current ITERThe charging process is terminated.
Automatic charging
Once the battery charging cycle is completed, the charger will remain off. If the input adapter is present, when the battery voltage is below the automatic charging threshold
VRECA new charging cycle starts automatically. After unplugging the input adapter, restart the charging cycle.
Charging status indication
The CXLB73308 has an open drain output for the charged state. Connect a current limiting resistor and an LED between VCC and this pin CAN interface.
When charging, the STAT pin shows LOW. When charging is complete or the charger is in sleep mode, the STAT pin shows HIGH. When charging in fault
The STAT pin flashes at 1Hz when paused in the condition.
input current adaptive
CXLB73308 detect the VIN pin. If the VIN pin voltage is higher than the VIN_UVP 150 ms rise threshold, the CXLB73308 is charged with the set
The flow starts charging. When the adapter is overloaded, the DRP pin drops below the internal reference 0.9V, CXLB73308 will reduce the charging current. We suggest
The R1/R2 ratio is around 4.1. Input Voltage Sensing As shown in FIG. 4, R1 and R2 are selected to set the input voltage threshold.
Temperature control
When the CXLB73308 junction temperature rises above 135°C, it begins to prevent further temperature rise by reducing the output power. If the junction temperature exceeds 150
C, will stop charging.
Shutdown mode
When the CE pin voltage falls below the charge enable threshold, the CXLB73308 shuts down. The entire regulator is closed.
Battery temperature protection
To protect the battery in charge mode, the CXLB73308 monitors the battery temperature via the CE/NTC pins. When the CE/NTC pin voltage exceeds the threshold,
The charging process will be paused. In addition, the STAT pin flashes at 1Hz to indicate a fault condition. Once the temperature returns to within the threshold range, the charging process
will recover.
4. Critical Circuit Design Guide
4.1. Charging voltage setting
4.1.1 The battery full charge voltage can be configured via the BATFB pin:
· If BATFB is grounded, the default setting is 2 series batteries (8.4V);
· If you need to customize the voltage, it can be set by external voltage dividing resistors RA and RS:
4.1.2 It is recommended to use 1% precision resistor to ensure voltage precision.
4.2. Charging current setting
The constant current charging current ICC is determined by the detection resistor RCS and the setting resistors RISET1 and RISET2:
For example, to set a charging current of 2A, RCS = 10mΩ,RISET1 = 2kΩ, and RISET2 = 1.5 kΩ can be selected.
4.3. Status indication and enable control
4.3.1. STAT Pin: Open drain output, can drive LED to indicate charging status:
· Low level: charging;
· High level: full or sleep;
· 1Hz flashing: fault or pause.
4.3.2. CE/NTC Pins: Support charging enable and battery temperature monitoring to enhance system safety.
4.4. Reference design
Note 1: Input current limit single-cell battery charging
WINE: 4.6V~5.5V
VBAT: 3V~4.2V
IIN_LIM: 2A
Note 2: Input current limit 2 string battery charging
WINE: 4.6V~12V
VBAT: 6V~8.4V
IIN_LIM: 2A
Note 3: Input current limit 3 series battery charging
WINE: 4.6V~12V
VBAT: 9V~12.6V
IIN_LIM: 2A
Note 4: Battery end current limit 4 string battery charging
WINE: 4.6V~20V
VBAT:12V ~ 16.8 V
Ibat_lim: 1A
5. PCB Layout and Thermal Recommendations
In order to improve the stability and anti-interference ability of the system, the following suggestions are made:
· The input capacitor is as close to VIN and PGND as possible to reduce the loop area;
· The current detection resistor RCS should be set close to the resistor to improve the current accuracy;
· Power ground (PGND) and signal ground (GND) should be laid out separately and connected at a single point under the chip;
· As far as possible to expand the grounding copper area, in order to facilitate heat dissipation.
In order to reduce interference problems and improve electrical performance, it is best to refer to the use guide for PCB.
1. The input decoupling capacitor is placed as close as possible to the CXLB73308(VIN pin and PGND) to eliminate interference at the input pins. by the input capacitor and
The loop area formed by GND must be minimized.
2. The current sensing resistor RCSResistance R as close as possible to the current settingISETfor better current accuracy.
The ground area on the PCB should be as large as possible for better heat dissipation.
6. typical application scenarios
CXLB73308 widely applicable:
· Mobile power supply and charging treasure: Support multi-string battery pack to improve output capacity;
· USB PD DeviceCompatible with all kinds of fast charging protocol, 9V/12V/20V input;
· Industrial Equipment & Power Tools: High temperature resistance and high reliability design;
· Automotive auxiliary power system: Wide input voltage to adapt to vehicle power fluctuations;
· Supercapacitor Charging Management: Support fast charging of high-voltage capacitor bank.
7.Package and pin function
EightConclusion
With its high integration, flexible configuration and comprehensive protection mechanism, the CXLB73308 provides an efficient and reliable solution for multi-string lithium battery charging system. Whether in consumer electronics or industrial and automotive fields, the chip can help developers build high-performance, compact power systems. For more information about CXLB73308 technical information, sample application or purchase information, please visitJTM-IC official website, we will provide you with professional technical support and high-quality service.
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