The CXLB73281 is a synchronous step-down lithium battery charging IC with a fixed frequency of 800kHz. The input voltage range is 4.0V ~ 6.0V, and the typical application is a 5V adapter. The built-in power MOSFET eliminates the need for external freewheeling diodes or high-precision sampling resistors, greatly simplifying peripheral circuit design. The chip supports an adjustable output current of up to 3.5A, and the charging voltage accuracy is ± 1%, which is widely used in various portable electronic devices.
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[ CXLB73281 ]"
CXLB73281: A 5V adapter for high-precision 3A lithium battery charging chip depth analysis
With the increasing popularity of portable electronic devices, an efficient, safe and stable battery charging management scheme has become the key to product design. As a high-efficiency synchronous buck charging IC designed for 5V AC adapter, CXLB73281 has become an ideal choice for mobile phones, tablet devices, digital cameras and other products with its 92% conversion efficiency, accurate voltage control and comprehensive protection functions. This paper will comprehensively analyze the technical characteristics, working principle, design points and typical applications of the CXLB73281.
1. Product Overview
The CXLB73281 is a synchronous step-down lithium battery charging IC with a fixed frequency of 800kHz. The input voltage range is 4.0V ~ 6.0V, and the typical application is a 5V adapter. The built-in power MOSFET eliminates the need for external freewheeling diodes or high-precision sampling resistors, greatly simplifying peripheral circuit design. The chip supports an adjustable output current of up to 3.5A, and the charging voltage accuracy is ± 1%, which is widely used in various portable electronic devices.
2. core features
2.1. High efficiency and high precision
· Switching frequency: 800kHz
· Charging efficiency:>92%
· Output voltage accuracy: ± 1% (typical 4.2V)
2.2. Three-stage charging management
· Eliminating current charging: when the battery voltage is less than 2.9V, pre-charge with 600mA small current
· Constant current charging: the current is set by an external resistor, up to 3.5A
· Constant voltage charging: the voltage is constant at 4.2V until the current drops to the termination threshold
2.3. Comprehensive system protection
· Input undervoltage/overvoltage protection
· Battery temperature monitoring (NTC support)
· Output short circuit protection
· Chip over-temperature and down-current protection
· Anti-backfilling and automatic recharging
2.4. Intelligent Status Indication
· Dual open-drain output: NCHRG (charging) and NSTDBY (full)
· Support red and green two-color LED indication, intuitive display of working status
2.5. Low power design
· Standby current: Typical 70μA
· Battery current in shutdown mode:<2μA
3. typical application scenarios
Mobile phones and tablets
The CXLB73281 supports 3A high current charging, which can quickly replenish power for smart devices. Its high efficiency and temperature protection function ensure the safe and reliable charging process.
Digital camera and portable audio
In video and audio equipment, the battery capacity is usually large. CXLB73281 constant-current constant-voltage charging mechanism with NTC temperature monitoring effectively extends battery life.
GPS devices and electronic dictionaries
Such devices require high power consumption and charging stability. CXLB73281 low standby current and adaptive input current control are ideal for such applications.
4. Critical Circuit Design Guide
4.1. Charging current setting
The charging current IBAT is determined by the PROG pin resistor RPISet, the common resistance and current corresponding relationship is as follows:
| RPI | IBAT |
|---|---|
| 1.08kΩ | 1A |
| 412Ω | 2A |
| 316Ω | 2.5A |
| 249Ω | 3A |
| 210Ω | 3.5A |
4.2. Temperature monitoring settings
4.2.1. TS pin connected to NTC thermistor, used to monitor battery temperature
4.2.2 Protection threshold:
· Low temperature:<45% VCC
· High temperature:>80% VCC
4.2.3 If temperature monitoring is not required, connect TS to VCC
4.3. float voltage compensation
In order to compensate the internal resistance of the battery and the line voltage drop, the external resistor R can be used.PVFine adjustment float voltage:
Recommended RPV= 1kΩ as the default configuration.
4.4. Typical application circuit diagram
5. PCB Layout and Thermal Design
Since the CXLB73281 is packaged in SOP8, the heat dissipation capability directly affects the continuous output capability of the maximum charging current. Here are the key layout recommendations:
5.1. Thermal pad design：
· Set 2.5mm × 6.5mm copper pads at the bottom of the chip
· Arrange 4 Φ1.2mm via holes with a hole spacing of 1.6mm
· When soldering, tin is poured from the back to ensure good contact between the chip heat sink and the PCB
5.2. Power Path Design：
· 22 μF Ceramic Capacitor Arrangement Nearby VCC and BAT Pins
· Power inductance with rated current ≥ 4A and low internal resistance (2.2μH ~ 10μH recommended)
5.3. Thermal Management：
· Avoid placing other heat sources around the charging IC
· Make full use of internal power layer and back copper heat dissipation
Detailed explanation of 6. protection mechanism
4.1. input adaptive protection
When the input voltage is lower than VINSL(typically 4.65V), the chip automatically reduces the charging current to prevent the adapter from overloading.
4.2. Short circuit and current limiting protection
· Input Current Limit: Peak 4.5A
· Output short circuit protection: output voltage <2.2V, the input current limit to 100mA
4.3. over-temperature protection
· Automatic downflow when junction temperature exceeds 145 ℃
· Stop charging when temperature> 150 ℃
4.4. Undervoltage lockout (UVLO)
When the input voltage is lower than 4V, enter the shutdown mode, and restart after the voltage is restored and higher than the battery voltage 120mV.
7. Status Indication and Fault Diagnosis
|
Charging state |
NCHRG (red light) |
NSTDBY (green light) |
|---|---|---|
|
Charging |
Bright |
Extint |
|
Full |
Extint |
Bright |
|
Fault * |
Extint |
Extint |
* Faults include: abnormal temperature, battery not connected, input undervoltage, etc.
8. to expand the application: white LED driver
CXLB73281 can also be used to drive white LED (such as 3W ~ 11W). When the input is 6V (such as 4 dry batteries), the chip works in constant current mode, and the output current is set by RPI, which is suitable for portable lighting and backlight systems.
9. package and pin function
VCC (Pin 1): Input supply voltage terminal. When the voltage difference between VCC and BAT pin is less than 30mV, the CXLB73281 will enter a low-power shutdown
mode, the current of the BAT pin will be less than 2uA.
PROG (pin 2): Maximum charging current setting, resistor resistance between 1K ~ 200ohm.
NSTDBY (pin 3): charging completion indicator terminal. When battery charging is complete, this pin is pulled low by an internal switch, indicating that charging is complete. No
The pin is then in a high impedance state.
NCHRG (pin 4): charging status indication terminal. When the charger is charging the battery, this pin is pulled low by the internal switch, indicating that the charging is being
proceed; otherwise the pin is in a high impedance state.
TS (Pin 5): Battery temperature sensing input. The TS pin is connected to the output of the battery's NTC sensor. If the voltage at the TS pin is less
45% of the input voltage or more than 80% of the input voltage means that the battery temperature is too low or too high, and the charging is suspended. If the TS is directly connected to VCC,
The battery temperature detection function is canceled, and other charging functions are normal. If the TS is directly connected to GND, the standby mode is entered and charging is terminated.
BAT (pin 6): Battery voltage detection terminal. A resistor is connected in series between the positive terminal and the pin of the battery to adjust the full voltage of the battery. The chip is
When the operation is prohibited or the sleep mode, the leakage current of the BAT pin is less than 2uA.
GND (pin 7): Power supply ground.
LX (pin 8): Built-in power MOSFET connection point. LX is the CXLB73281 current output connected to the external inductor as the battery charging current input
End.
10. Summary
With its high integration, high efficiency, comprehensive protection functions and flexible design options, the CXLB73281 has become an ideal choice for lithium battery charging management in the 5V adapter scenario. Whether in consumer electronics, industrial equipment or portable instruments, its excellent performance and reliability can enable products.
If you need to obtain CXLB73281 samples, technical information or apply for design support, please visitJTMIC official website (jtm-ic.com）Or contact our technical support team.
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