SLYT844 September 2023 LMG3522R030 , TMS320F280049C
A loss of power in data center server power-supply units can interrupt everything from entertainment to financial transactions to home security systems. Specifications such as the V2 Power Shelf Specification from the Open Compute Project (OCP) [1] emphasize the need to reduce server downtime with robust AC dropout control algorithms. In addition, the need for cost-effective solutions in data centers to improve power factor correction (PFC) light load and peak efficiency while shrinking passive components is becoming difficult with conventional continuous conduction mode control [2-8].
To address this problem, TI developed a gallium nitride (GaN)-based high-density design using two-phase integrated triangular current mode (iTCM) PFC (Figure 1) [9]. Low-value inductors operating at a high frequency have enabled the high efficiency (>99%) and power density (120 W/in3) of this design. These small inductors present a unique problem to AC dropout recovery in that only a few microseconds of switch on-time can result in over 70 A of switch current. In addition, any delays in timing can also result in significant reverse current, further exacerbating PFC recovery. Keeping the current levels at a safe magnitude and preventing reverse current required the development of a new solution to the AC dropout and recovery problem. This article discusses this solution with lab verification data based on the Variable-Frequency, ZVS, 5-kW, GaN-Based, Two-Phase Totem-Pole PFC Reference Design [10], for which Table 1 lists the primary components and system specifications.
Parameters | Value |
---|---|
AC input | 90 V-264 V |
Line frequency | 50-60 Hz |
DC output | 400 V |
Maximum power | 5 kW |
Holdup time at full load | 20 ms |
Lg, low-frequency inductor | 140 µH |
Lb, high-frequency inductor | 14 µH |
Cb, high-frequency blocking capacitor | 1.5 µF |
Total harmonic distortion (THD) | OCP v3 |
Electromagnetic interference (EMI) | European standard (EN) 55022 Class A |
Operating frequency | Variable, 75 kHz-1.2 MHz |
Microcontroller | TMS320F280049C [11] |
High-frequency GaN field-effect transistors (FETs) (S11, S12, S22, S21) | LMG3526R030 [12] |
Low-frequency silicon FETs (S3, S4) | IPT60R022S7XTMA1 |
Dimensions | 38 mm ´ 65 mm ´ 263 mm |
Power density | 120 W/in3 |