Many power-supply ICs are designed to work with a wide range of applications. However, some applications require precisely controlled voltages at high currents, calling for a more tailor-made power-supply solution.

Optical transceivers in data centers, for instance, require a unique power supply. Load transients must be regulated quickly to ensure that the supply voltage deviates only slightly from its nominal value. This is also the case for DRAM and other memory chips, which are evolving to use lower supply voltages. All in all, meeting these requirements is a challenging task for a power supply. Figure 1 shows the application of an optical transceiver in a wireless communication system or data center.

These applications tend to have special requirements for supply-voltage accuracy. The switch-mode power supply (SMPS) in Figure 1 generates the voltage for the optical transceiver. The buck converter features a DC accuracy of ±0.25% over the entire permissible temperature range of –40 to +150°C when the output voltage is set between 0.6 and 1.375 V.

The wide temperature range is necessary because power electronics in data centers are often packed as tightly as possible. While these power converters have high efficiency, they still dissipate some power as heat, which can raise the temperature of the circuit to very high levels.

For accurate control, it’s important to ensure high accuracy for load transients in addition to DC accuracy. These can be achieved with a fast control loop of the voltage converter and with many high-quality output capacitors. But since these capacitors can be costly and take up valuable space, engineers often attempt to speed up the regulation of the power supply.

On-Time Valley Current-Mode Control

In the LT7176, fast control is achieved by an on-time valley current-mode control (Fig. 2). Compared to other solutions, an approximate 30% reduction in the overshoot and undershoot of the output voltage can be attained thanks to load transients.

To limit electromagnetic interference (EMI) without limiting efficiency, the device leverages Analog Devices' Silent Switcher technology to enable fast switching transients with very low radiated emissions. The fast switching transitions lead to low switching losses of the power supply. As a result, it can operate a high switching frequency of up to 3 MHz without experiencing excessive losses.

To further reduce output-voltage ripple, a variant of the LT7176 can be used: The LT7176-1 is almost identical, featuring a pair of phase-shifted channels with the same maximum output current of 24 A. However, two inductors are required for this solution. The advantage is that these inductors only need to handle half the total power; therefore, engineers can specify devices with a lower overall height. The vertical space savings can be helpful for applications that are limited in height.

In addition to accurate voltage regulation, high reliability of voltage conversion is important. Using a digital connection of the LT7176, the state of the input and output voltage, input current, device temperature, and other fault states and operating conditions can be queried.

It’s also possible to execute various settings of the device through the existing PMBus connection. This includes setting the output voltage, a current limit, switching on and off, soft start and soft stop, and many other parameters such as control-loop compensation.

Figure 3 shows the graphical user interface LTpowerPlay, which allows the circuit to be evaluated and configured with different settings.

Despite the many different SMPS ICs on the market, there are always applications where only a specialized solution can fully meet the requirements. The LT7176 and LT7176-1 present a new solution offering high output currents and control accuracy with low converter losses and low radiated emissions, as well as advanced control through digital interfaces.