Simplified Block Diagram
Click any title below to view the detail page where available.
- Peak Current-Mode Control, Forward/Flyback PWM Controllers
- Internal 1% Error Amplifier
- 100kHz to 600kHz Programmable ±8% Switching Frequency
- Switching Frequency Synchronization Up to 1.2MHz
- Programmable Frequency Dithering for Low-EMI Spread-Spectrum Operation
- PWM Soft-Start, Current Slope Compensation
- Programmable Feed-Forward Maximum Duty-Cycle Clamp, 80% Maximum Limit
- Frequency Foldback for High-Efficiency Light-Load Operation
- Internal Bootstrap UVLO with Large Hysteresis
- 100µA (typ) Startup Supply Current
- Fast Cycle-by-Cycle Peak Current-Limit, 35ns Typical Propagation Delay
- 115ns Current-Sense Internal Leading-Edge Blanking
- Output Short-Circuit Protection with Hiccup Mode
- 3mm x 3mm, Lead-Free, 16-Pin TQFN
- Flyback/Forward DC-DC Converters
- IP Phones
- PoE IEEE 802.3af/at Powered Devices
- Power Devices in PoE/Power-over-MDI
- Security Cameras
- Wireless Access Nodes
The devices are suitable for both isolated and nonisolated designs. Because the devices have an internal error amplifier with a 1% accurate reference, they can be used in nonisolated power supplies without the need for an external shunt regulator.
An enable input (EN) is used to shut down the devices. Programmable soft-start eliminates output voltage overshoot. The MAX5975A has an internal bootstrap UVLO with large hysteresis that requires 20V for startup, while the MAX5975B requires 10V for startup.
The switching frequency for the ICs is programmable from 100kHz to 600kHz with an external resistor. For EMI-sensitive design, use the programmable frequency dithering feature for low-EMI spread-spectrum operation. The duty cycle is also programmable up to the 80% maximum duty-cycle limit. These devices are available in 16-lead TQFN packages and are rated for operation over the -40°C to +85°C temperature range.