AC-DC and DC-DC Peak-Current-Mode Converters for Flyback/Boost Applications

Description

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The MAX17498A/MAX17498B/MAX17498C devices are current-mode fixed-frequency flyback/boost converters with a minimum number of external components. They contain all the control circuitry required to design wide input voltage isolated and nonisolated power supplies. The MAX17498A has its rising/falling undervoltage lockout (UVLO) thresholds optimized for universal offline (85V AC to 265V AC) applications, while the MAX17498B/MAX17498C support UVLO thresholds suitable to low-voltage DC-DC applications.

The switching frequency of the MAX17498A/MAX17498C is 250kHz, while that of the MAX17498B is 500kHz. These frequencies allow the use of tiny magnetic and filter components, resulting in compact, cost-effective power supplies. An EN/UVLO input allows the user to start the power supply precisely at the desired input voltage, while also functioning as an on/off pin. The OVI pin enables implementation of an input overvoltage-protection scheme that ensures that the converter shuts down when the DC input voltage exceeds the desired maximum value.

The devices incorporate a flexible error amplifier and an accurate reference voltage (REF) to enable the end user to regulate both positive and negative outputs. Programmable current limit allows proper sizing and protection of the primary switching FET. The devices support a maximum duty cycle greater than 92% and provide programmable slope compensation to allow optimization of control loop performance. The devices provide an open-drain PGOOD pin that serves as a power-good indicator and enters the high-impedance state to indicate that the flyback/boost converter is in regulation. An SS pin allows programmable soft-start time for the flyback/boost converter. Hiccup-mode overcurrent protection and thermal shutdown are provided to minimize dissipation under overcurrent and overtemperature fault conditions. The devices are available in a space-saving, 16-pin (3mm x 3mm) TQFN package with 0.5mm lead spacing.

Key Features

• Peak Current-Mode Converter
• Current-Mode Control Provides Excellent Transient Response
• Fixed Switching Frequency
  • 250kHz: MAX17498A/MAX17498C
  • 500kHz: MAX17498B
• Flexible Error Amplifier to Regulate Both Positive and Negative Outputs
• Programmable Soft-Start to Reduce Input Inrush Current
• Programmable Voltage or Current Soft-Start
• Power-Good Signal (PGOOD)
• Reduced Power Dissipation Under Fault
  • Overcurrent Protection
  • Thermal Shutdown with Hysteresis
• Robust Protection Features
  • Programmable Current Limit
  • Input Overvoltage Protection
• Optimized Loop Performance
  • Programmable Slope Compensation
• High Efficiency
  • Low R_DSON, 175mΩ, 65V Rated Internal n-Channel MOSFET
  • No Current-Sense Resistor
• Optional Spread Spectrum
• Space-Saving, 16-Pin (3mm x 3mm) TQFN Package

Applications/Uses

• Front-End AC/DC Power Supplies for Industrial Applications (Isolated and Nonisolated)
• Telecom Power Supplies
• Wide Input Range DC Input Flyback/Boost Industrial Power Supplies