CXAC85217B is a PWM current type controller optimized for low-power switching power supplies, using standard DIP8 and SOP8 packaging, combining high performance and low cost advantages. The standby power of the chip is extremely low, fully meeting the standby power consumption requirements of international energy efficiency standards such as Energy Star, and suitable for various power supply application markets worldwide.
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[ CXAC85217B ]"
CXAC85217B PWM Current Mode Switching Power Controller: An Efficient and Energy saving Power Solution
In the context of today's pursuit of high efficiency and energy conservation in electronic devices, the performance of power management chips directly affects the energy efficiency performance of the entire system. CXAC85217B, as a highly integrated and high-performance PWM current mode switching power supply controller, is an ideal choice for low-power switching power supply applications such as chargers and power adapters due to its excellent energy efficiency performance and comprehensive protection functions. This article will delve into the technical characteristics, working principles, and application design of the chip, providing engineers with a complete reference solution.
1、 Chip Overview and Core Advantages
CXAC85217B is a PWM current type controller optimized for low-power switching power supplies, using standard DIP8 and SOP8 packaging, combining high performance and low cost advantages. The standby power of the chip is extremely low, fully in line with the requirements; Energy Star "; The standby power consumption requirements of international energy efficiency standards are applicable to various power supply application markets worldwide.
This controller integrates multiple advanced functions, including cutting-edge blanking, peak current compensation, synchronous slope compensation, frequency jitter technology, and soft start. It also provides comprehensive protection mechanisms such as overvoltage, undervoltage, overtemperature, overload, open-loop, and output short circuit, ensuring the safe and reliable operation of the system under various working conditions.
2、 Core technical features
2.1. High efficiency and low-power design
• Ultra low starting and operating currentThe typical starting current is only 5 A, and high resistance starting resistors can be used to reduce system power consumption
• Jump cycle working modeAutomatically reduce the switching frequency under no-load or light load conditions, significantly reducing switching losses
• Optimized VDD managementBuilt in VDD overvoltage protection and clamp circuit to ensure stable and safe power supply
2.2. Accurate current control technology
• Cycle by cycle current limitationReal time monitoring and limiting peak current to prevent overcurrent damage
• Leading edge blanking (LEB) functionBuilt in 350ns blanking time to eliminate current detection spike interference during switch moments
• Peak current compensationOutput characteristic differences under high and low temperature conditions through dynamic ramp voltage balancing
• Synchronous slope compensationEffectively prevent subharmonic oscillation in CCM mode and improve system stability
2.3. Excellent EMI performance
• Built in TikTok functionSwitching frequency jitter within the range of 63kHz to 71kHz disperses harmonic energy and reduces EMI peak
• Fixed frequency oscillatorTypical operating frequency of 67kHz, optimized system design and filtering requirements
2.4. Comprehensive protection mechanism
• Multiple voltage protectionIncludes VDD overvoltage, undervoltage protection, and output overvoltage protection
• Abnormal state protectionProvide overload, open-loop, output short circuit, and over temperature protection functions
• Automatic recovery mechanismAfter troubleshooting, the system can automatically restart, improving product reliability
3、 Pin function and electrical parameters
3.1. Pin configuration (SOP8/DIP8 package)
• FB (Pin 1)Voltage feedback input terminal, connected to optocoupler to adjust duty cycle
• NC (pins 2, 6, 7)Empty pin, it is recommended to hang or ground it
• VDD (pin 3)Chip power input, working range 10-26V
• GATE (pin 4)Drive output, external power MOSFET
• CS (Pin 5)Current detection input terminal, external detection resistor
• GND (pin 8)Chip grounding terminal
3.2. Key electrical parameters
• starting voltage: 15V (typical value)
• Turn off voltage: 9V (typical value)
• operating frequency: 67kHz (typical value)
• Maximum duty cycle: 80% (typical value)
• over-temperature protection: Junction temperature -40 ℃ to+150 ℃
4、 System working principle and design points
4.1. Initiation and workflow
After the system is powered on, the VDD capacitor is charged by starting the resistor. When the VDD voltage reaches 15V, the chip starts working. A typical startup configuration is 1.5-2MΩ The combination of a starting resistor and a 10 μ F/25V electrolytic capacitor can meet the starting requirements of most applications.
4.2. Light load jump cycle working mode
Under no-load or light load conditions, when the FB voltage is below 1.1V and VDD is above 10.5V, the system enters a jump cycle mode, intermittently stopping switch operations and significantly reducing standby power consumption. When the load increases and the FB voltage exceeds 1.3V, the system automatically returns to normal operating mode.
4.3. EMI optimization design
The built-in jitter function of the chip causes a 6% amplitude jitter in the switching frequency range of 63kHz to 71kHz, effectively dispersing harmonic energy and reducing EMI radiation at specific frequency points, helping the system easily pass EMC certification.
4.4. Detailed explanation of protection mechanism
• VDD overvoltage/undervoltage protectionWhen VDD exceeds 27V or falls below 9V, the system enters a protective state
• Overload and open-loop protectionWhen the FB voltage remains above 3.7V for 50ms, the system will shut down the output until VDD under voltage restarts
• Cycle by cycle current limitationReal time monitoring of current through CS pin to ensure that peak current does not exceed the limit in each cycle
5、 Typical application examples
5.1. 12V/1.5A power adapter solution
• input voltage：90-264VAC
• Output specifications：12V/1.5A
• no-load loss：<0.3W
• Full load efficiency：>80%
5.2. Transformer design (EF20 magnetic core)
• Primary inductor：800μH± 10%（PIN1-PIN3）
• leakage inductance：<80μ H
• Winding structure：
· N1：Φ 0.3mm× 35T（PIN1→PIN2）
· N2：Φ 0.3mm× 35T（PIN2→PIN3）
· N3：Φ 0.15mm× 11T（PIN8→PIN10）
· Shielding layer:Π 0.15mm wrapped around one layer
6、 PCB Design Guide
• VDD bypass capacitorIt should be placed close to the VDD and GND pins of the chip to ensure stable power supply
• Current detection pathThe path from the CS pin to the detection resistor should be short and straight to reduce noise interference
• Power LayoutPower ground and signal ground should be wired separately, with single point grounding to reduce common mode interference
• Heat dissipation considerationsAppropriately increase the copper foil area of DRAIN pins to improve heat dissipation performance
7、 Market competitive advantage
CXAC85217B has significant advantages among similar products:
• cost-effectiveProvide highly competitive prices while ensuring performance
• high integrationReduce the number of peripheral components, lower system costs and PCB area
• Excellent energy efficiency performanceStandby power consumption<0.3W, meeting the latest energy efficiency standards
• Comprehensive protection functionIntegrating multiple protection mechanisms to enhance system reliability
• Flexible packagingProvide DIP8 and SOP8 packaging options to adapt to different production processes
8、 Conclusion
CXAC85217B, as a high-performance and low-power PWM current mode switching power supply controller, provides an ideal solution for low-power switching power supply applications with its excellent technical characteristics and comprehensive protection functions. Whether it's a mobile phone charger, power adapter, or other consumer electronics power supply, this chip can provide stable and efficient performance, helping products meet energy efficiency standards around the world.
With the increasingly strict energy regulations and the continuous improvement of energy efficiency requirements by consumers, CXAC85217B will continue to play an important role in the field of power management, providing core technical support for green and energy-saving electronic products.
If you need to obtain CXAC85217B samples, technical information or apply for technical support, please visitJTM-IC official websiteWe have a professional technical team that can provide you with comprehensive product selection guidance and design support, helping your product win a competitive advantage in the global market.
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