How a 16 V, 8 A Silent Switcher µModule Regulator is Ideal for Low Noise Applications

摘要

Low noise performance is a crucial aspect of many power applications. Analog Devices’ pioneering Silent Switcher® technology has enabled the development of μModule® regulators with innovative circuit design and packaging techniques, offering high efficiency while reducing electromagnetic interference. The unique approach makes these regulators less susceptible to PCB layout variations, resulting in simplified designs and enhanced performance. ADI’s step-down DC-to-DC μModule regulator, capable of delivering 8 A maximum output current from a 3 V to 16 V input, is an ideal compact solution for high current and noise-sensitive applications.

Introduction

Low noise is an increasingly common requirement for many power supply applications, such as high precision data converters, medical devices, and RF systems. Traditionally, switch-mode DC-to-DC converters were known for their inherent noise, making them unsuitable for noise-sensitive applications. ADI’s pioneering Silent Switcher technology has enabled the development of μModule regulators that offer exceptional performance for low noise applications.

The LTM4702 is a step-down DC-to-DC μModule regulator capable of delivering 8 A maximum output current from a 3 V to 16 V input. It employs Silent Switcher architecture with internal hot loop bypass capacitors to achieve both low electromagnetic interference (EMI) and high efficiency. The module contains a current-mode controller, power switching elements, a power inductor, and a modest amount of input and output capacitance.

The output voltage can be regulated from 0.3 V to 5.7 V. This IC is available in a tiny 6.25 mm × 6.25 mm × 5.07 mm BGA package with a –40°C to +125°C operating junction temperature range.

Typical Application Example

Figure 1 shows a typical application schematic. It operates at about 800 kHz switching frequency. The switching frequency can be easily adjusted by a resistor (RT pin resistor to AGND). The SET pin sources a precision 100 µA current that flows through an external resistor connected between the SET pin and GND. The regulator output voltage will strictly follow the SET pin voltage, which is determined by I_SET × R_SET. Using a SET pin bypass capacitor reduces sensitivity to any parasitic coupling of voltage spikes onto the SET pin. A SET pin bypass capacitor also soft starts the output and limits inrush current. The efficiency vs. load current curves are shown in Figure 2.

In the example circuit, the SYNC pin is tied to GND for pulse-skipping mode, improving efficiency at light loads. This device can also operate in forced continuous mode (FCM) for fast transient response and full frequency operation over a wide load range. To enable FCM, tie the SYNC pin to INTV_CC or > 3 V, or float the SYNC pin.

Driving the SYNC pin with a clock source can synchronize the regulator to an external clock. The device may be synchronized over a 300 kHz to 3 MHz range. The regulator will run in FCM while synchronized to an external clock.

The LTM4702 features a programmable power good by using a single resistor across the V_OUT pin and the PGSET pin. The power good output (PG) will be low when the output voltage is outside of the ±7.5% regulation window. The IC also has other user-friendly features, including enable/shutdown control, a selection of internal loop compensation or external loop compensation, and an internal temperature monitor.

Ultralow Noise Silent Switcher

The Silent Switcher family is engineered with innovative design and packaging techniques to offer high efficiency while reducing EMI. This unique approach makes these regulators less susceptible to PCB layout variations, resulting in simplified designs and enhanced performance.

The LTM4702 has an ultralow noise architecture to obtain exceptional low frequency (<100 kHz) output noise. A single resistor sets the output voltage, providing unity gain operation over the output range, resulting in virtually constant output noise independent of the output voltage.

Figure 3 shows the radiated EMI performance.

Multiphase Parallel Operation for Higher Output Current

Two or more devices may be paralleled to supply a higher current. Figure 4 shows an example: two μModule regulators are in parallel to produce up to 16 A load current. In the example, the CLKOUT signal is connected to the SYNC pin of the following IC to line up both the frequency and the phase of the paralleled system. The two paralleled regulators are running at 180° out of phase, with the PHMODE pin tied to the ground. Excellent current sharing is achieved with the current-mode control architecture by connecting the compensation pins together. The SET pins of the paralleled devices are tied together with only one SET resistor.

Conclusion

The LTM4702 is a complete 8 A step-down Silent Switcher µModule regulator. It can provide a precisely regulated output voltage programmable via one external resistor from 0.3 V to 5.7 V. Low EMI and low noise features make it ideal for high current and noise-sensitive applications, such as telecom/datacom systems, RF power supplies, and high speed/high precision data converter applications. With the compact size, high efficiency, and low external component count of this µModule regulator, users will save significant board space and design time.

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