Multi-Output Switchmode Regulator and Controller ICs

Multiple output controller ICs consist of two or more of switchmode dc-dc converters in a single package. They can be controllers that employs external power switches or regulators with an internal power switch. One possibility is a 5V output and a 3.3V output for processor and logic applications.

These devices are used in ac powerline and battery-powered applications. Some of the more sophisticated ICs include supervisory and power sequencing capability.

Among the features found in multiple output controller ICs are:

  • Fixed or adjustable outputs
  • Soft-start
  • Fixed or variable switching frequency
  • Undervoltage lockout (UVLO)
  • Thermal protection
  • Power Good output
  • Current limit
  • Overvoltage protection
  • Enable/disable
  • Independently regulated outputs
  • Power sequencing control

Following are typical examples of multiple-output switchmode regulator and controller ICs.

1. A dual current mode PWM step-down dc-dc converter with internal 2A power switches, this IC operates from a 3.6V to 25V input, enabling it to regulate a wide variety of power sources such as four-cell batteries, 5V logic rails, unregulated wall transformers, lead acid batteries and distributed-power supplies. The two regulators share common circuitry including input source, voltage reference and oscillator, but are otherwise independent.

The two switchers are current mode step-down regulators, so the feedback loop controls the peak current in the switch during each cycle. This current mode control improves loop dynamics and provides cycle-by-cycle current limit.

Current mode PWM architecture provides fast transient response with simple compensation components and cycle-by-cycle current limiting. Frequency foldback and thermal shutdown provide additional protection. Each regulator generates a Power-Good signal when its output is in regulation, easing power supply sequencing and interfacing with microcontrollers and DSPs.

Both converters are synchronized to a single 1.1MHz oscillator and run with opposite phases, reducing input ripple current. The 1.1MHz constant frequency minimizes both switching noise and the size of the external components making it ideal for noise-sensitive applications. Constant frequency and ceramic capacitors also combine to produce low, predictable output ripple voltage.

Each regulator has independent shutdown and soft-start circuits. If the RUN/SS1 and RUN/SS2 (run/soft-start) pins are both tied to ground, the IC is shut down and draws 30µA from the input source tied to VIN. Internal 2µA current sources charge external soft-start capacitors, generating voltage ramps at these pins. If either RUN/SS pin exceeds 0.5V, the internal bias circuits turn on, including the internal regulator, 1.25V reference and 1.1MHz master oscillator. In this state, the IC draws 3.5mA from VIN, whether one or both RUN/SS pins are high. Neither switching regulator will begin to operate until its RUN/SS pin reaches ~0.8V.

2. A dual constant frequency, synchronous step down dc-dc converter, this IC uses a current mode architecture with an operating frequency set at 1.5MHz that can be synchronized to an external oscillator. The high switching frequency allows the use of tiny, low cost capacitors and inductors 2mm or less in height. Its two channels share the same clock and run in-phase. The selectable Mode pin, allows the user to tradeoff noise for efficiency.

The IC is intended for low power applications, it operates from 2.5V to 5.5V input range. Each output voltage is adjustable from 0.6V to 5V. Its internal synchronous 0.35W on-resistance, 1A power switches provide high efficiency without the need for an external Schottky diodes.

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