One-step conversion to core voltage

Abstracts

This paper describes the possibility of converting high voltages (e.g. 48 V or 54 V) directly to core voltages (typically below 1 V) in one step. This conversion not only saves space and improves efficiency, but also reduces the costs associated with designing the input power rails. Deploying a high-voltage bus consumes less copper to carry the same power than using a 12 V intermediate bus.

What do data centre digital processors, high-end FPGAs, larger artificial intelligence (AI) processors and supercomputers have in common? The answer is that they all require a power supply to provide the core voltage. Kernel voltages are typically below 1 V and current levels range from under 100 A to 1 kA and above.

Building high-current, low-voltage power supplies is difficult. High conversion efficiencies are essential to minimise heat dissipation requirements. In addition, voltage converters must be compactly designed to minimise parasitic alignment effects between the power supply circuitry and the load (processor), which facilitates fast response to load transients and better voltage regulation.

Figure 1 shows a common voltage converter architecture that first converts a 48 V supply voltage to a 12 V DC link voltage and then regulates it to a core voltage of less than 1 V in a second step.

Figure 1.Voltage conversion architecture for converting from 48 V to 0.8 V core voltage in two steps

Despite the high efficiency of each step, the overall efficiency of the two-step conversion is low. Due to cumulative losses, even if the efficiency of each conversion step reaches 93 per cent, the total efficiency is only about 87 per cent (0.93 × 0.93 = 0.8649).

Figure 2. one-step voltage conversion architecture for converting 48 V to 0.8 V core voltage

Figure 2 shows another conversion architecture that uses the μModule LTP8800-4A, which is capable of directly converting a 48 V voltage to a 0.8 V core voltage in a single step. The efficiency of this solution can reach more than 90 per cent when the load current is 100 A. The module can also be used as a power supply for the core. Moreover, the module can provide output currents of up to 200 A. Multiple such devices can operate in parallel to generate currents of 1,000 A or more - critical for some high-end processors.

Dedicated core voltage converters, such as the LTP8800-4A, can generate core voltages from 0.5 V to 1.1 V in one step at currents up to 200 A. The LTP8800-4A can also be used as a step-down converter, which can be used in a variety of applications. Conventional buck converter circuits struggle to cope with very low duty cycles. When converting from 48 V to 0.5 V, the duty cycle is typically only about 1%, which poses a significant circuit design challenge. Due to the inherent constraints of switching regulators (e.g., minimum on-time), it is difficult to achieve such low pulse width ratios (duty cycles) at higher switching frequencies, making it difficult to achieve the desired level of efficiency.

Eliminating the DC link voltage simplifies the system configuration, with the circuit requiring only one power converter stage to complete the conversion. This approach not only saves space, but also reduces copper requirements as the high supply voltage of 48 V or 54 V is fed directly into the core voltage converter, thus optimising costs.

Figure 3. Compact size with LTP8800-4A module

Figure 3 illustrates a small footprint solution using the LTP8800-4A module. The use of μModule devices allows for excellent power supplies and avoids the complexity of traditional circuit design. The resulting circuit is compact and easy to integrate on boards adjacent to digital loads.

Modern core voltage converters, such as the previously mentioned μModule devices, provide advanced digital control via PMbus connections for real-time monitoring of voltage, current, temperature and faults. An internal EEPROM stores various settings and error logs. In addition, the digital connection supports fine-tuning of the power converter's control loop.

Reach a verdict

The new module converts 48 V directly to the core voltage, providing a compact and efficient power architecture option.