“This article discusses the need for distributed power networks and the role of POL power devices. It then introduces a class of POL DC/DC converters from TDK Corporation that use advanced packaging techniques to achieve the required performance characteristics. The article also discusses their salient properties and shows how designers can deploy them to successfully meet their POL power delivery requirements.
Author: Art Pini
Big data servers and applications like machine learning, artificial intelligence (AI), 5G phones, IoT, and enterprise computing often require powerful ASICs, FPGAs, GPUs, and CPUs, which in turn require low voltage, high current, and High power density in a compact package. In order to ensure the power integrity of the entire system, distributed power management systems are currently used to introduce DC/DC power directly into the point-of-load (POL), which is a high-performance processor. So there can be many of these DC/DC power converters ON a board, so the problem facing the designer is how to make these devices as small as possible to save board space. At the same time, they need to meet performance, latency, thermal, efficiency and reliability requirements while simplifying the design process and reducing cost.
Solutions to this problem matrix combine high-performance semiconductors and passive components, using advanced packaging techniques to achieve a higher level of system integration. This has proven to enable a smaller size, lower form factor, while enhancing thermal management, compared to other technologies currently available. At the same time, this comprehensive approach controls design-in costs, including inventory management and development time.
This article discusses the need for distributed power networks and the role of POL power devices. It then introduces a class of POL DC/DC converters from TDK Corporation that use advanced packaging techniques to achieve the required performance characteristics. The article also discusses their salient properties and shows how designers can deploy them to successfully meet their POL power delivery requirements.
Why use a POL DC/DC converter power supply
Computers, servers, and other digital devices increasingly use FPGAs, ASICs, and other advanced IC devices that require multiple supply voltages that system power supplies cannot. Also, they need these voltages to be in the correct order with minimal delay. System power supplies typically provide some fixed voltages, such as 1, 3.3, and 5 volts. A typical FPGA requires a Voltage range of 1.2 to 2.5 volts (Figure 1).
Figure 1: A typical FPGA requires multiple voltages for specific functions within the processor. The processor shown uses eight dedicated power inputs, with three different voltages. (Image credit: Art Pini)
At a minimum, the FPGA needs to be powered separately for its core and I/O sections. The FPGA core in the example runs at 1.2 volts and the I/O functions run at 2.5 volts. In addition, six other power levels are required for its auxiliary circuits. Obviously, placing the seven power supplies in close proximity to the FPGA places a burden on the board layout design. Another issue to consider is heat dissipation, which requires the power supply to be small and efficient.
Patented technology enables unique system integration
To meet the size requirements, TDK has developed a proprietary design for the POL DC/DC converter that foregoes the side-by-side discrete component layout. Instead, it takes a 3D integration approach, based on its semiconductor Embedded Substrate (SESUB) System-in-Package (SiP) technology. A buck converter is formed by embedding a high-performance Semiconductor containing a pulse-width modulation (PWM) controller and mosfets into a 250-micrometer (μm) circuit board substrate. The circuit output inductors and Capacitors are also integrated into the 3D layout, resulting in an ultra-compact thermally enhanced package (Figure 2).
Figure 2: Patented SESUB technology integrates an advanced power controller IC and MOSFETs into a 250 μm substrate, together with the circuit output inductors and capacitors to form a highly integrated DC/DC converter module. (Image source: TDK Corporation)
A Unique POL Power Solution
TDK uses SESUB as the basis for its μPOL (pronounced “micro-POL”) series of miniature DC/DC power modules. The product family, model FS140x-xxxx-xx, has 19 options with output voltage levels of 5, 3.3, 2.5, 1.8, 1.5, 1.2, 1.1, 1.05, 1, 0.9, 0.8, 0.75, 0.7 and 0.6 volts. They support a continuous load current of 3 to 6 amps (A), depending on the model, and come in a package size of 3.3 x 3.3 x 1.5 millimeters (mm) (Figure 3).
Figure 3: The μPOL DC/DC converter measures only 3.3 x 3.3 x 1.5 mm and can handle up to 15 watts of power. (Image source: TDK Corporation)
Due to its unique physical design, this family of DC/DC converters can provide power densities of up to 1 watt per square millimeter, allowing this small package to handle up to 15 watts of power.
The nominal output voltage is factory set to within ±0.5%. An I2C interface is included to allow local control of the converter. The output voltage can be adjusted in steps of ±5 millivolts (mV) from the preset nominal voltage.
FS1406 μPOL Converter Internal Structure Overview
The functional block diagram of the FS1406-1800-AL 1.8-volt DC/DC converter shows that despite its small size, the device contains many complex circuit functions (Figure 4).
Figure 4: The functional block diagram of the FS1406-1800-AL DC/DC converter shows the complexity of the circuit, including the internal PWM, I2C port, control logic, and output MOSFETs. (Image source: TDK Corporation)
The FS1406-1800-AL has a nominal output of 1.8 volts, a continuous load capability of 6A, and its output voltage is programmable via I2C from 0.6 to 2.5 volts. It requires an input voltage of 4.5 to 16 volts and has a specified operating temperature range of -40°C to +125°C.
At the heart of this DC/DC converter is a proprietary PWM modulator designed to provide fast transient response. The operating frequency of the PWM modulator is proportional to the output voltage of the converter. It includes internal stability compensation to match various output Capacitor types without the need for an external compensation network, making it “plug and play”. The PWM output of the modulator drives the gates of the mosfet power devices. As previously mentioned, the output filter Inductor is contained within the package, further reducing external components.
Note that the FS1406 includes an internal low dropout (LDO) Regulator that operates at about 5.2 volts to power the internal circuitry and MOSFETs.
Additionally, designers should be aware of built-in protection features including soft-start protection, “power good” status line, overvoltage protection, pre-bias start-up, thermal shutdown with auto-recovery, and thermally compensated overcurrent protection with hiccup mode . If an overcurrent event is detected, hiccup mode shuts down the power supply for a fixed period of time and repeats the sequence until the fault is cleared.
The I2C interface is used to set the output voltage. It also allows setting system optimization parameters, including parameters for startup and protection functions.
The FS1406 family is fully integrated, trimmed at the factory to its specified target voltage, and does not require an output voltage divider. The design does require the addition of a minimal output capacitor to ensure acceptable output ripple and load regulation. It also requires an input capacitor to handle its input current requirements. Figure 5 shows the minimum required addition of circuit components.
Figure 5: In a typical application, the FS1406 μPOL DC/DC converter family requires at least the addition of input and output capacitors. (Image source: TDK Corporation)
The input and output capacitors should have low equivalent series resistance. Multilayer ceramic capacitors are recommended. The FS1406 datasheet provides detailed guidance on the calculation of input and output capacitor values.
Evaluation boards help designers get started quickly
The evaluation board for the 1.8-volt version of the μPOL converter is the EV1406-1800A, which provides a DC/DC converter design with a 1.8-volt output and a 12-volt input source. It has an output current of 0 to 6 A and dimensions of 63 x 84 x 1.5 mm (Figure 6).
Figure 6: The EV1406-1800A evaluation board measures 63 x 84 x 1.5 mm; the μPOL DC/DC converter is highlighted in yellow to draw attention to this tiny device. (Image source: TDK Corporation)
Given the size and power capabilities of a μPOL, we can easily fit multiple of these devices around an FPGA or ASIC. In addition to providing a design example, the evaluation board has open through-hole component locations for the user to experiment with input and output capacitance values. It also has a header for selecting the FS1406-1800’s internal bias supply or external voltage source. Another header provides easy access to the I2C interface.
I2C programming dongle
As a design aid, TDK offers the TDK-MICRO-POL-DONGLE I2C programming board for changing the output voltage in steps of ±5 mV. It also allows programming of system protection parameters. The dongle is used with a free GUI software package provided by TDK, which simplifies the tuning of the converter.
For designers who require high reliability and integrated POL power distribution while minimizing the impact on board space, the 19 DC/DC converters in the TDK mPOL series provide the right solution for a variety of applications plan. The family supports 14 common output voltage levels, each adjustable in ±5 mV steps via the I2C port. μPOL’s patented unique architecture is based on SESUB, enabling high power density and minimal support component requirements.