MAX1634EAI+T

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DC-DC switch controllers are widely used in modern electronic devices, such as consumer electronics and industrial equipment, to provide the ability to accurately control the power supply voltage, along with providing the capability to create multiple power supplies in a single-chip solution or package. The MAX1634EAI+T is a popular high-efficiency, programmable step-down (buck) DC-DC controller that meets the demands of today\'s consumer electronics, automotive, health care, networking, and industrial markets. This application note examines its features, operation, and typical application circuit.

Features

The MAX1634EAI+T is a flexible, highly integrated, synchronous buck controller. Its features include the following:

• Wide input voltage range: +4V to +20V
• Output voltage range: 0V to VIN
• Current mode control with adjustable slope compensation
• Wide range adjustable switching frequency: 25kHz to 1MHz
• Selectable voltage feedback reference: 0.5V, 0.625V, 0.75V
• Integrated low-resistance Power MOSFETs
• Programmable soft-start
• Thermal shutdown

Operation

The MAX1634EAI+T is a buck converter that operates by continuously switching between the input supply voltage, VIN, and the output voltage, VOUT. The switching is controlled by an internal current-mode pulse-width modulator (PWM). The charge stored in an inductor connected between input and output pins is used to step down VIN to VOUT. The inductor also acts as a reservoir, supplying charge during times when VIN is not greater than VOUT, i.e., during the "off time" or "slope time" phase.

The MAX1634EAI+T has a built-in full-bridge driver, capable of switching currents up to about 3A. The device features a low-resistance NDMOS transistor, providing high efficiency and a low-profile external solution.

The driver includes a logic input to enable the output voltage. To control the output voltage, the device has an internally regulated 0.5V to 3V reference and two control signal inputs for setting the output voltage. A feedback comparator inside the device compares the load voltage feedback signal with the voltage reference, and the difference sets the on-time of the internal pulse-width modulator (PWM) loop.

The device incorporates a programmable soft-start circuit and a thermal shut-down circuit. The soft-start circuit limits the output inrush current during the startup, while the thermal shut-down circuitry protects the device and the system in case of excessive temperature conditions.

Typical Application Circuit

The typical application circuit for the MAX1634EAI+T is shown in Figure 1. This circuit is designed to power a load with a regulated +5V supply and draw a current of up to 2A. The circuit includes an input capacitor to filter input noise, an EMI filter, a current sensing resistor to sense the output current, and an output capacitor.

The output ripple of this circuit is about 150mV (peak to peak) for a load current of 1A. The typical output voltage ripple is slightly higher for a heavier load, and slightly lower for a lighter load.

Conclusion

The MAX1634EAI+T is an integrated step-down (buck) DC-DC controller IC, designed for use in consumer electronics, automotive, health care, networking, and industrial applications. It provides adjustable current and voltage feedback, adjustable switching frequency, programmable soft-start, and thermal shut-down. Its wide input voltage range and low-resistance internal MOSFETs provide high efficiency and small solution size. Its typical application circuit example in Figure 1 shows a 2A buck converter solution.

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