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CXSD62678: Industrial grade solution for 600V voltage resistant synchronous rectification and voltage reduction chip with 20A high current outputJzS嘉泰姆
 JzS嘉泰姆

          In harsh scenarios such as high-power LED screens, industrial control systems, and Ethernet PoE,High voltage inputandHigh current outputThe DC-DC converter is the core power engine.CXSD62678As a revolutionary synchronous rectification and voltage reduction chip600V ultra-high voltage withstandThe20A continuous outputand0-300kHz adjustable frequencyThree major characteristics redefine the standard for high-performance power supplies. This article will delve into its technological breakthroughs and design practices.JzS嘉泰姆

1、 Disruptive technological highlights

1. Synchronous rectification architecture: IntegrationHigh end+low-end MOS driver(HO/LO pin), replacing traditional Schottky diodes, conversion efficiencyIncrease by 8% -12%Especially optimized for 5V/12V/24V output scenarios.JzS嘉泰姆

2.600V ultra-high voltage withstandVB pin support4-600V wide inputDirectly adapted to 380V industrial bus, electric bicycle battery pack, and three-phase power system, eliminating the need for a front-end voltage reduction circuit.JzS嘉泰姆

3. Flexible frequency adjustmentExternal single capacitor can be used for setting67-300kHz operating frequency(Formula:f=18× 10⁶/Cp， Cp unit pF), balancing EMI and efficiency requirements.JzS嘉泰姆

4. Intelligent protection mechanism:Cycle by cycle current limiting(180mV threshold)+ Short circuit hiccup protection， VCC capacitor adaptively adjusts the turn off time to avoid overheating and damage to the power transistor.JzS嘉泰姆

2、 Core application scenarios

1. Industrial control systemProvide 24V/20A stable power supply for PLC and servo drives, and withstand 600V surge impact.JzS嘉泰姆

2. Ethernet PoE++Supports 802.3bt 90W standard, with a single chip capable of converting 48V to 12V/7.5A.JzS嘉泰姆

3. LED display screen5V/20A output drives high-density LED chips, with adjustable frequency to suppress flicker.JzS嘉泰姆

4. Electric bicycle converterThe 72V battery pack can be directly reduced to 12V with an efficiency greater than 92%.JzS嘉泰姆

3、 Key Design Guidelines

4、 Electrical characteristics and packaging

1. Limit parametersVB withstand voltage 600V, VCC withstand voltage 20V, operating temperature-45℃~125℃.JzS嘉泰姆

SOP16 encapsulation：10× 6.3mm compact size, supporting high power density layout.JzS嘉泰姆

3. Key Performance：JzS嘉泰姆

5、 Analysis of program advantages

1. Energy Efficiency Revolution:Compared to asynchronous solutions, synchronous rectification reduces costs60% freewheeling loss， 20A output efficiency reaches95%(Tested on a 5V system).JzS嘉泰姆

2. Security upgradeJzS嘉泰姆

a. VCC capacitor intelligent management short circuit turn off time (the larger the C, the longer the turn off time), protecting the power transistor;JzS嘉泰姆

b. 180mV high-precision current detection, response speed<250ns.JzS嘉泰姆

3. Design simplification:Integrated 3.3V/50mA reference source, eliminating LDO; Single capacitor frequency modulation reduces external oscillation circuit.JzS嘉泰姆

6、 Application design considerations and component parametersJzS嘉泰姆

1   REF3.3V input capacitorJzS嘉泰姆
        Placing a high-frequency small capacitance bypass capacitor to ground at the REF3.3V pin will reduce high-frequency noise at the REF3.3V terminal. The high-frequency bypass capacitor is optionalJzS嘉泰姆
Use 1uF ceramic capacitors and arrange the board as close as possible to the chip pins; REF3.3V input terminal.JzS嘉泰姆
2   VCC energy storage capacitorJzS嘉泰姆
      CXSD62678   Requirement  Place a VCC pin terminal to ground; 10uF capacitor, mainly used for startup to; VCC pin for energy storage charging and normal operationJzS嘉泰姆
Stable working time; The working voltage of the VCC pin, and the capacitor has a certain effect on output short-circuit protection. When the output is short circuited, the VCC pin will dropJzS嘉泰姆
Electricity, chips enter  In UVLO mode, the size of the capacitor will affect the time it takes for the chip gap to turn on the power transistor when the output is short circuited. The larger the capacitor, the longer the gapJzS嘉泰姆
The longer the time, the smaller the heat generated by the power tube, and conversely, the heat generated by the power tube will increase.JzS嘉泰姆
3   startup processJzS嘉泰姆
        When the R21 resistor is suspended, the input power is supplied externally; R2 resistor pair; The external capacitor of VCC pin starts charging, at this time; CXSD62678   The chip will beJzS嘉泰姆
Low static current working mode consumes approximately; 50uA working current, internal only; UVLO circuit is working, other oscillators and; PWM modules are all locatedJzS嘉泰姆
In the closed state, the output voltage is zero, and when the capacitor voltage on the VDD pin is charged to; When the voltage is above 4.6V, the chip starts working normally and starts oscillatingJzS嘉泰姆
Device, PWM module and feedback processing circuit, output voltage stabilization output, and output voltage through external diodes to; VCC pin provides  VCC workerJzS嘉泰姆
As a power source, the startup process ends.JzS嘉泰姆
        2-pin external resistor can adjust the startup voltage and shutdown voltageJzS嘉泰姆
Starting voltage calculation formula: 1.2V x (R20+R21)/R21+18uA * R20JzS嘉泰姆
Calculation formula for closing voltage: 1.2V x (R20+R21)/R21JzS嘉泰姆
Turn off the voltage design to the normal output voltage; 70%-90%JzS嘉泰姆
4   Calculation of switching frequency of oscillator Cr capacitorJzS嘉泰姆
      CXSD62678 only requires an external capacitor to set the PWM operating frequency, and uses a constant current source internally to charge and discharge the Cp capacitor as shown in Figure 8.4a,JzS嘉泰姆
The constant current source that injects current provides approximately 36uA of current internally to charge the Cp capacitor, while the constant current source that pulls current provides approximately 720uA of current internally to discharge the CT capacitorJzS嘉泰姆
The relationship between electricity, approximate operating frequency, and capacitance is expressed by the formula f=(18 x10^six）/Cp determination (the capacitance unit of this formula is ); pF)， A capacitor with Cp=270pF corresponds to PWMJzS嘉泰姆
The working frequency is approximately 67KHz.JzS嘉泰姆

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5   Output peak current limitJzS嘉泰姆
      CXSD62678   The peak current limit of the high-end output of the chip is determined by the internal resistance or series resistance of the high-end MOS transistor; R7 determines the peak currentJzS嘉泰姆
The formula is  IPK=180mV/(high-end ); Internal resistance of MOS transistor or; R7）；     The peak current limit of the low-end output of the chip is determined by the low-end; The internal resistance of MOS transistor determines,JzS嘉泰姆
The relationship between peak current is; IPK=180mV/(low-end); MOS tube internal resistance).JzS嘉泰姆
6   Output short circuit protectionJzS嘉泰姆
          When the output is short circuited and the R21 resistor is suspended, CXSD62678   Operate at maximum peak current limit output, while; The voltage of VCC will lose power due toJzS嘉泰姆
The output voltage can no longer pass through the diode; The VCC pin provides power, CXSD62678   The static working current of the chip quickly leaks out; VCC pin powered onJzS嘉泰姆
Voltage of capacitance, when; The voltage of VCC pin is lower than; At 3.8 V, CXSD62678   The chip will be completely shut down; PWM output, while the input power is turned on externallyJzS嘉泰姆
Re adjust the dynamic resistor; The capacitor on the VCC pin begins to charge when; The voltage of VCC pin is higher than; 4.6V， Chip restart  PWM， If the output persistsJzS嘉泰姆
In a short circuit state, the chip will open the gap to turn on the power transistor. At this point; The CXSD62678 chip will be in current limiting and short-circuit protection mode.JzS嘉泰姆
7   Output inductanceJzS嘉泰姆
      CXSD62678   Working in continuous mode;   The selection of inductance can be based on the following formula:JzS嘉泰姆
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In the formula,  Vin   Is the input voltage, Vout is the output voltage, Fs is  PWM operating frequency, Iripple is the peak to peak value of current ripple in the inductor, usuallyJzS嘉泰姆
Choose Iripple to not exceed 30% of the maximum output current.JzS嘉泰姆
8   Synchronous rectification MOS transistorJzS嘉泰姆
        Adopting synchronous rectification; MOSFET   Replacing traditional asynchronous converters with freewheeling diodes greatly improves power conversion efficiency; synchronous rectificationJzS嘉泰姆
MOSFET selection with low internal resistance and low junction capacitance can provide; CXSD62678   The voltage regulator provides good performance.JzS嘉泰姆
9   output capacitorJzS嘉泰姆
      The output capacitor Co is used to filter the output voltage, so that; The DC-DC converter provides a relatively stable output of DC power to the load. Choose this optionJzS嘉泰姆
Choose as low a capacitance as possible; The capacitance of ESR is mainly determined by the ripple requirements of the output voltage, and can be determined by the following formula:JzS嘉泰姆
 In the formula, Delta; Vo is the output voltage ripple,Δ IL is inductor current ripple, Fs is; PWM operating frequency, ESRJzS嘉泰姆
It is the equivalent series resistance of the output capacitor.JzS嘉泰姆
10   Output voltage regulation settingJzS嘉泰姆
      The output voltage of CXSD62678 is set by two voltage divider resistors on the FB pin, and the reference voltage of the internal error amplifier is 1.2V, as shown in the figure;   Figure    8.10aJzS嘉泰姆
As shown, the output voltage;   Vout=（1+R1/R2）*1.2V， To set the output voltage to; 12.12V， Can be set; R1 is; 9.1K, R2 is; 1K， loseJzS嘉泰姆
Output voltage; Vout=（1+9.1/1）*1.2V=12.12V。JzS嘉泰姆

JzS嘉泰姆

ConclusionJzS嘉泰姆
        CXSD62678“ High voltage direct drive+synchronous rectification;  Architecture solves the problem of efficient conversion of industrial power supplies. Its flexible frequency adjustment and intelligent protection features provide a milestone solution for LED drivers, PoE power supply, and electric transportation systems. By optimizing MOS selection and inductor design, the potential of 20A output can be fully utilized to meet the requirements of the next generation of highly reliable power supplies.JzS嘉泰姆

Innovative ApplicationsIn solar micro inverters, it supports conversion from 600V photovoltaic input to 24V/20A; Paired with gallium nitride MOS transistors, a 200W+PD fast charging module can be achieved, with an efficiency exceeding 96%.JzS嘉泰姆

      For detailed PDF specifications, please contact us. You can also receive free samples and technical support！   JzS嘉泰姆

Product packaging diagram;JzS嘉泰姆

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Circuit schematic diagram;JzS嘉泰姆

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   Selection Guide for Related Chips;                  More related products .....JzS嘉泰姆

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