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PMIC - Voltage Regulators - DC DC Switching Regulators

The LTC3428EDD#PBF (hereafter referred to as the 3428EDD) belongs to the DC-DC switching regulators family of integrated circuits. This product is the latest addition to Linear Technology\'s SwitchReg family of DC/DC controller ICs. A DC/DC switching regulator is a voltage regulator which employs switching technology to transform an input voltage into a regulated output voltage with higher efficiency than a linear regulator. The 3428EV is an adjustable version of the 3428EDD, which may be configured as either a synchronous or non-synchronous buck regulator or a switching boost regulator.

Device Overview

The 3428EDD is a monolithic integrated circuit (IC) which utilizes two P-Channel power MOSFETs and two N-Channel power MOSFETs to operate as a synchronous or non-synchronous buck regulator or a switching boost regulator. When configured as either a buck or boost regulator, the 3428EDD is capable of regulating an output voltage from 0.60 V to 6.25 V with a light load efficiency above 95%.

The 3428EDD features a current mode architecture which provides fast response to load step transients, high efficiency, and a low drop-out voltage. Regulated output voltages can be adjusted using the reference input voltage. Additionally, built-in soft start and current limit provide protection against output voltage overshoot and short circuit events.

Application Fields

The 3428EDD is ideal for portable systems which require tight regulation of output voltage over varying load conditions. It is highly suited for battery powered applications which require tiny size, efficiency, and high accuracy regulation of the battery voltage.

The 3428EDD is also a good solution for portable medical equipment, smartphones, cellular base stations, digital cameras, notebooks, and other personal electronic devices which require efficient and accurate DC/DC converter solutions.

It can also be used in DC/DC architectures which require abundant performance and tight load and line regulation over varying input voltages.

Utilization

The 3428EDD has several external components which must be provided to complete the regulator circuit. The external MOSFETs and gate drivers provide the high-side and low-side drive signals. Additionally, an external capacitor is required for the switching frequency and loop compensation. Depending on the operating mode, either an external coulomb counter or an external resistor is required.

To illustrate the utilization and operation of the 3428EDD, a buck converter application circuit is presented in Figure 1. The application circuit consists of an inductor, two MOSFETs, two diodes, and two capacitors. The output voltage is regulated by the Loop Compensation and PWM ON circuitry of the device, which is controlled by the Output Regulation Pin (REG). The external components of this application circuit are as follows:

• A coupling capacitor is used to couple the current through the primary side (Low Side) MOSFET.
• An output capacitor is used to filter the output voltage to reduce ripple.
• An external resistor is used to set the current limit, which is controlled by the PWM ON pin (PON).
• An external coulomb counter is used to monitor the battery voltage, which is controlled by the Output Regulation Pin (REG).

Working Principle

When the input voltage is applied to the 3428EDD, the main regulator blocks pulls up and down alternately the gate voltage of the power MOS switch, synchronizing with the frequency defined by the voltage of the external compensator capacitor. When the MOS switch is pulled up, the energy stored on the primary inductor is transferred to the output, causing an increase in the output voltage. When the MOS switch is pulled down, the current still continues to flow and the energy stored on the output capacitor decreases, thereby decreasing the output voltage. The output voltage is then regulated by the Loop Compensation and PWM ON pin, which is adjusted according to the input voltage, load, and output voltage.

The device provides current limit protection by controlling the PWM between the high and the low level using an external current-sense resistor. If the current levels exceed the programmed current limit, the device will enter the redefined PWM state, which will keep the maximum current at the previously set level. Additionally, the device also provides soft-start for a smoother power up. During soft start, the output voltage rises in a gradual ramp, which prevents inrush current from damaging the external components.

Conclusion

The Linear Technology LTC3428EDD#PBF is an adjustable, highly integrated DC/DC switching regulator. Its adjustable output current, low drop-out voltage, and current-mode control greatly reduce switching losses and improve system efficiency by eliminating additional external components. Due to its features and small size, the 3428EDD is ideally suited for portable systems, medical equipment, smartphones, and other personal devices which require efficient and accurate DC/DC converter solutions.

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