feature

50% duty cycle variable frequency control half-bridge resonant converter topology High efficiency through zero voltage switching (ZVS) Internal Unifet 8482 with fast recovery type; S body diode Fixed dead time (350ns) up to 300kHz optimized for mosfet Automatic restart operation of all protections at operating frequency External LVCC protection functions: over voltage protection (ovp), over current protection (ocp), abnormal over current protection (AOCP), internal thermal shutdown (TSD)

application

PDP and LCD TV station-style computer and server adapters Telecom power supply

describe

The fsfr-us series is a highly integrated power switching resonant converter designed for high efficiency half bridges. Providing everything necessary to build a reliable and robust resonant converter, the fsfrus series simplifies design and increases productivity while enhancing performance. FSFR-US series power mosfet with fast recovery type body combined diode, high side gate drive circuit, precise current controllable oscillator, frequency limit circuit, soft start and built-in protection function. The high-end gate drive circuit has common-mode noise cancellation capability to ensure stable operation, and the fast-recovery body diode of the noise-immune mosfet improves reliability conditions for abnormal operation while minimizing the impact of reverse recovery. Using Zero Voltage Switching (ZVS) technology greatly reduces switching losses and improves efficiency significantly. ZVS also significantly reduces switching noise, enabling small electromagnetic interference (EMI) filters. The fsfr-us series can be applied to various resonant converter topologies such as series resonant, parallel resonant converters and llc resonant converters.

Function description

1. Basic operation: The FSFR-US series is designed to complementarily drive high-side and low-side mosfet with 50% duty cycle. Fixed dead time of 350ns introduced between successive conversions

2. Internal Oscillator: The FSFR-US series uses a current controlled oscillator, internally, the voltage of the RT pin is regulated to 2V, and the charge/discharge current of the oscillator capacitor, CT, is copied from the RT pin using the current mirror ( ICTC). Therefore, the switching frequency increases with ictc.

3. Frequency setting: Figure 17 shows the voltage gain curve of a typical resonant converter, where the gain is inversely proportional to the switching frequency in the ZVS region. The output voltage is adjustable by adjusting the switching frequency. Typical circuit configuration for the RT pin, where an optocoupler transistor is connected to the RT pin to modulate the switching frequency.

To prevent excessive inrush current and overshoot of the output voltage at startup, increase the voltage gain of the resonant converter. Since the voltage gain of the resonant converter is inversely proportional to the switching frequency, soft start is achieved by reducing the switching frequency from the initial high frequency (Fiss) until the output settles the voltage. The soft-start circuit consists of connecting the RC series network on the RT pin, the fsfr-us series also has an internal soft-start of 3ms to reduce the initial period of current overshoot during the initial period, and an external soft-start circuit with an initial frequency of 40kHz 4. Automatic restart: FSFR- The US series can restart even if any built-in protection is triggered by an external supply voltage. It can be seen from this that once any protection is triggered, the M1 switch opens and the VI converter. css starts to discharge until vcss drops to vcsl through css. Then, all protections are reset, m1 is turned off, and the VI converter is restored at the same time. fsfr-us restarts the switch with a soft start. If the protection level occurs when VCSS is under VCSSL and VCSSH, the switch is terminated immediately and VCSS continues to increase until vcsh is reached, then css is emitted by M1.

5. Protection circuit: The fsfr-us series has several self-protection functions, such as overcurrent protection (OCP), abnormal overcurrent protection (AOCP), overvoltage protection (ovp) and thermal shutdown (TSD). These protections are auto-restart mode protections once a fault condition is detected, the switch will terminate while the mosfet remains off. When the lvcc falls into the lvcc 10V or the AR signal stops the voltage is high, the protection resets. When the lvcc reaches the startup voltage of 12.5v. 5.1 Over-current protection Sensing loose voltage drops -0.58V, OCP IS trigger and Mossfelt still exist protection with 1.5µs delay to prevent initial shutdown at start 5.2 AOCP-Current Protection secondary rectifier diode short , a wide and extremely high DT current can be passed through the flip-flop as early as before the OCP. trigger. When the loose voltage is induced, it keeps delaying the downstream drop -0.9v5.3 overvoltage protection (ovp): when the lvcc reaches 23V, the ovp is triggered. Use this protection to use up to fps when the transformer auxiliary winding is supplying VCC. 5.4 Thermal Shutdown (TSD): The mosfets and a packaged control chip enable the control IC to detect the mosfets. Thermal shutdown is triggered if the temperature exceeds about 130°C. 6. Resistive Current Sensing: The FSFR-US series senses the leakage current as a negative voltage, as shown in Half-wave sensing allows the power consumption of the sensing resistor at low full-wave with less switching noise in the sensing signal. Control ICs 7. Printed Circuit Board Layout Guidelines: Load imbalance issues can be due to radiated noise from the main pipeline, unequal main transformer inductance, leakage on the secondary side of the transformer, etc. Between them, this is what controls the components near the RT pins by the primary current flow pattern on the PCB layout. This is caused by the direction of the magnetic field on the component when the high current and low side MOSFETs are turned on in turn. The magnetic field induces current through, into, or out of the RT pins in opposite directions, which makes each mosfet different. It is strongly recommended to separate control components near the RT pins from the main current flow pattern on the PCB layout. An example of a duty cycle balance situation is shown.