LT3759 wide input voltage range boost/Negative output/SEPIC controller can operate with input voltages as low as 1.6V

Introduction
Many of today's electronic devices require a negative output or positive output converter, and sometimes both are required. In addition, they must operate with a variety of power supplies, including USB, wall adapters, alkaline batteries, and lithium batteries.

In order to produce different polarity outputs from variable input voltages, power designers often use a variety of voltage regulator ICS, resulting in an increase in the variety of inventory components.

The lt®3759 can operate within the input voltage range of 1.6V to 42V and use the same feedback pin to control positive or negative output, reducing inventory and simplifying design.

The device also integrates many popular features (e.g. soft start, adjustable frequency, and synchronization) into a compact footprint. The LT3759 is available in a 5mm x 4mm 12-pin MSE package and can be used in a variety of configurations.

For example: Boost, SEPIC, flyback, and cuk topologies.

Wide input voltage range and internal LDO

The wide input range of the LT3759 simplifies the design of power supplies that must be compatible with many input sources.

Because the LT3759 contains two internal low dropout (LDO) voltage regulators that are powered by VIN and drive pins, there is no need for an external regulator or a slow charge hysteresis starter for simple start-up and biasing.

The LT3759 's internal INTVCC current limiting function circuitry prevents the IC from generating excessive on-chip power dissipation.

Detection of the output voltage becomes easy

The LT3759 incorporates a novel FBX pin architecture that simplifies the design of negative output and positive output converters. It contains two internal error amplifiers (one detects positive outputs and the other detects negative outputs),

and allows the FBX pin to be connected directly to the voltage divider from a positive or negative output, eliminating any confusion associated with positive or negative output detection and simplifying the board layout.

You only need to determine the output polarity and topology, and the rest of the work can be done to LT3759.

Adjustable/Synchronous Switching frequency

Converters typically need to operate at a specific frequency, especially in RF communication applications, which are sensitive to spectral noise in certain frequency bands.

Furthermore, if the area of the available converter is limited, working at a higher frequency can also allow smaller components to be used, thereby reducing the required board-level space and output ripple.

If the power loss is an indicator of concern, performing a switching operation at a lower frequency can reduce switching losses and thus improve efficiency.

The switching frequency range is 100kHz to 1MHz and can be set using a single resistor connected between the RT pin and the ground.

In addition, the device can be synchronized to an external clock via the sync pin.

Precision UVLO and soft-start

The input supply undervoltage lockout (UVLO) for sequencing or initiating overcurrent protection can be easily implemented by using a resistor divider from VIN power supply to drive the Uvlo.

When VIN is at the desired Uvlo rising threshold voltage, the divider output generates a 1.22V voltage on the Uvlo pin.

The UVLO pin has an adjustable input hysteresis, allowing the IC to ignore a settable input supply voltage drop before deactivating the converter.

During the UVLO process, the IC is deactivated while VIN quiescent current drops to 1µa or less.

The SS pin enables the use of the soft start function, which reduces peak input current when starting or recovering from a failure condition, and avoids output voltage overshoot.

The SS pin suppresses the inrush current by reducing the switching peak current. The soft start function allows the output capacitor to gradually charge to its final value in this way.

A 2.5v~15v to 12V SEPIC Converter

Figure 1 shows a 2.5v~15v input with LT3759, 12v/2.5a output SEPIC power supply. The typical efficiency of this converter is shown in Figure 2. Figure 3 shows the switching waveform during the output short circuit.

The graph shows that once the output voltage is shorted to ground, the switching frequency will immediately turn back to One-third of the normal frequency. This feature enhances the short-circuit performance of the CUK and Sepic converters.

A 1.8v~ 4.5V to 5v/2a step-up Converter Figure 4 shows a converter with a 4.5V to low to 1.8V input to 5v/2a output.

For applications where the converter output voltage is higher than the input voltage, the LT3759 is configured as a boost converter. The switching frequency of the 500kHz allows the use of small inductors and output capacitors.

Conclusion

The LT3759 is a general-purpose IC that integrates a rich set of unique features within a slim 5mm x4mm 12-pin MSE package.

The device accepts a wide input voltage range of 1.6V to 42V and features low shutdown current and frequency foldback under light load conditions.

The LT3759 is ideal for wide input voltage applications, from single-cell lithium-ion battery-powered systems to automotive, industrial, and telecom power supplies.

Its high level of integration creates a solution for the number of simple and low components for boost, SEPIC and negative output converters.

LT3759 wide input voltage range boost/Negative output/SEPIC controller can operate with input voltages as low as 1.6V