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CXAC85257: high performance resonant half-bridge controller core technology analysis9qF嘉泰姆

In the design of high-performance switching power supplies such as LCD TVs, AC-DC adapters, and server power supplies, the resonant half-bridge topology has become the mainstream solution due to its low EMI and high conversion efficiency. As a two-terminal controller optimized for this topology, CXAC85257 provides engineers with high-reliability power management solutions through innovative frequency conversion control and multiple protection mechanisms.9qF嘉泰姆

1. core characteristics and working principle9qF嘉泰姆

1. Accurate frequency conversion control9qF嘉泰姆

A. provides strict 50% complementary duty cycle, and the high/low side MOSFET is alternately turned on with a phase difference of 180 °9qF嘉泰姆

B. Operating frequency up to 500kHz, adjustable frequency range via external capacitor CF and resistor network (RFmin/RFmax)9qF嘉泰姆

c. Fixed dead time (0.3μs typical) ensures soft switching characteristics and reduces high-frequency switching losses9qF嘉泰姆

2. Energy Smart Management9qF嘉泰姆

a. Burst Mode: Automatically enter intermittent working state when light load/no load (Figure 8-6)9qF嘉泰姆

▲ STBY pin voltage <1.25V stop switching action9qF嘉泰姆

▲ The average frequency can be reduced to hundreds of Hz, no-load power consumption is reduced by more than 50%9qF嘉泰姆

B. PFC linkage control: Turn off the PFC pre-regulator through the PFC_STOP pin (open set output), saving an additional 0.5-1W power consumption9qF嘉泰姆

2. multi-layer protection mechanism9qF嘉泰姆

1. Two-level over-current protection (OCP)9qF嘉泰姆

a. primary response (ISEN>0.8V): soft-start capacitor CSS discharges, and the frequency increases instantaneously to limit energy transmission9qF嘉泰姆

B. Secondary lock (ISEN>1.5V): completely shut down the output, need to restart the power to unlock9qF嘉泰姆

2. Programmable fault delay9qF嘉泰姆

A. DELAY pin external capacitor CDELAY (Figure 8-11)9qF嘉泰姆

B. trigger system shutdown when overload duration exceeds the set threshold (about 100ms when CDELAY = 1μF)9qF嘉泰姆

3. Critical protection interface9qF嘉泰姆

a. Latch off (DIS pin):>1.85V immediate latch off for OVP/OTP design9qF嘉泰姆

B. Bus detection (LINE pin)：9qF嘉泰姆

▲ PWM disabled at <1.25V, forced shutdown at> 6V9qF嘉泰姆

▲ 15μA hysteresis current to achieve precise voltage window control9qF嘉泰姆

Key Points of 3. Engineering Design9qF嘉泰姆

1. Oscillator Configuration Formula9qF嘉泰姆

RFmin = 1/(3 × C_F × f_min)
RFmax = RFmin/((f_max/f_min)-1)

2. Soft start optimization(Figure 8-8)9qF嘉泰姆

a.CSS in series with RSS to set the startup frequency (typical f_start = 4 × f_min)9qF嘉泰姆

B. Non-linear frequency attenuation to avoid output voltage overshoot9qF嘉泰姆

3. Current detection scheme9qF嘉泰姆

4. typical application scenarios9qF嘉泰姆

1. Large screen display device：9qF嘉泰姆

a. Support LCD/PDP TV power supply 650V high voltage drive9qF嘉泰姆

B. Burst mode meets EU CoC V5 Tier 2 no-load specification (<75mW)9qF嘉泰姆

2. Data Center Power：9qF嘉泰姆

a.-0.3A/0.8A drive capability directly drives MOSFET9qF嘉泰姆

B. Latched shutdown prevents server power cascading failures9qF嘉泰姆

3. Industrial power module：9qF嘉泰姆

a. Wide temperature range of -40 ℃ ~ 125 ℃9qF嘉泰姆

B. SOP16 package saves PCB space (see Figure 9-1 for dimensions)9qF嘉泰姆

5. packaging and compatibility9qF嘉泰姆

RoHS compliant SOP16L package, key parameters:9qF嘉泰姆

1. High-side suspension drive: 650V withstand voltage (VBOOT pin)9qF嘉泰姆

2.VCC working range: 8.8-17V (typical 15V)9qF嘉泰姆

3. Drive peak current: 0.8A current/0.3A current9qF嘉泰姆

4. Switching speed: rising edge 60ns/falling edge 30ns9qF嘉泰姆

Conclusion9qF嘉泰姆
CXAC85257 efficiency and reliability of the resonant converter in a wide load range are solved by the cooperation of frequency conversion control and multiple protection mechanisms. Its burst mode energy-saving technology and PFC linkage control are particularly in line with the green needs of modern power supplies, providing the core driving force for power supply design in the era of industrial 4.0.9qF嘉泰姆

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   Product packaging diagram9qF嘉泰姆

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   Circuit schematic9qF嘉泰姆

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