LTC3859IFE

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LTC3859IFE Application Field and Working Principle

The LTC3859IFE is a monolithic dual synchronous step-down switching regulator controller and true linear regulator solution. It integrates dual synchronous step-down switching regulators, plus a true linear regulator controller, which synchronize to a single external clock. This allows smooth transitions between the two, eliminating any current spikes, as well as providing excellent transient and steady state performance. This device is suitable for designing dual output non-isolated DC/DC converters.

Application Field

The LTC3859IFE dual synchronous step-down switching regulator controller is particularly suitable for designs requiring wide input voltages and dual outputs. It is well-suited for low voltage microprocessor, digital signal processor (DSP) core supplies as well as that of its I/O interfaces in personal computers, servers, telecommunications and industrial control systems. It is also suitable for any other system requiring dual output power supplies in which multiple output voltage options are desired. The LTC3859IFE is available in a 16-pin narrow body SOIC package.

Working Principle

The LTC3859IFE includes two synchronous, phase-shifted PWM controllers, an analog linear regulator controller, and a compensation network. The two independent PWM controllers feature phase-shift control, allowing for smooth transitions from one controller to the other, and have a switching frequency of up to 1MHz. The linear regulator can be used for output voltages up to 3.2V and has a precision reference for ultra-high accuracy. An onboard reference is used for the linear controller, allowing for very small and low cost designs.

The two independent PWM controllers work together in phase-shift control mode to ensure a smooth transition between them. Each controller features high-current totem pole gate drivers, programmable slew rate control, a space vector modulator, current sensing, adjustable frequency, and programmable soft-start. The dual PWM controllers allow for operation with a wide variety of external MOSFET types, as well as low ESR output capacitors.

The linear regulator operates at a fixed frequency of 400kHz and it integrates 3rd-order PWM modulator, a comparator for 2ms cycle-by-cycle current limit, a final drive stage, a reference comparator and a low-level precision Vref current source. It has a small spread spectrum capability to reduce system EMI and can be disabled by the PWM.

The LTC3859IFE has a wide range of protection features to ensure reliable operation. It includes an over-voltage protection (OVP) which prevents the output from being damaged in the event of an overvoltage condition on the output. It also includes high-side current sensing which gives better accuracy than low-side current monitoring. Other features include an adjustable frequency limit to prevent the converter from going into an overmodulation condition, undervoltage lock-out (UVLO) and over-temperature protection (OTP). A soft-start feature is also included to prevent output current surges when the device is enabled. In addition, the LTC3859IFE has an enable/disable feature which supports auto-flow-through operation, allowing the converter to be enabled and disabled without causing a power transient.

Conclusion

The LTC3859IFE is a dual synchronous step-down switching regulator controller and true linear regulator solution, perfect for low voltage microprocessors and digital signal processor (DSP) core supplies, as well as for other systems requiring dual output power supplies. It includes two synchronous, phase-shifted PWM controllers, an analog linear regulator controller, and a compensation network, with a wide range of protection features to ensure reliable operation. This device is available in a 16-pin narrow body SOIC package.

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