14 POWER CAPACITORS www.analog.com Issue 2 2025 Power Electronics Europe www.power-mag.com An Accurate Active Voltage Positioning Control Reduces up to 50% Output Capacitance for Module Regulators Sin Keng Lee, Staff Engineer, and Zhijun (George) Qian, Senior Manager, Analog Devices Abstract This article introduces an accurate series active voltage positioning (AVP) implementation method applied on a Module® regulator. This method achieves a fast load transient response, minimal board space, and an all ceramic capacitor solution. Compared with a shunt AVP design, this series AVP provides a significantly accurate load line accuracy, which greatly improves the output voltage accuracy. The measured results for the load transient response are presented. Introduction Active voltage positioning (AVP), or active droop technology, regulates the power supply output at higher voltage at light load and lower voltage at heavy load. One major benefit of implementing AVP control is to improve the load transient response and reduce output capacitance since AVP allows more room for the power supply to respond to the load transients. A Module regulator is a complete, tested, and qualified power supply in a package solution. Fast load transient response, minimal board space, and an all ceramic capacitor solution are preferred by Module regulator telecom and data centre applications. However, it is challenging to meet all these requirements with traditional non-AVP control. This article introduces an accurate series AVP implementation method by adding two resistors to the feedback control loop. The advantage of this series AVP method is that load line accuracy is almost independent of the gm amplifier gain variations, while other AVP implementation methods like the shunt AVP 1 would suffer from poor load line accuracy if the gm amplifier gain has large variations. After implementing this series AVP, up to 50% output capacitance could be reduced while peak-to-peak output voltage transient is also slightly improved. Only ceramic capacitors would be needed due to 50% less capacitance, which greatly improves system reliability and cost since the aluminum electrolytic capacitor is much less reliable and higher cost than the ceramic capacitor. Another benefit to implementing AVP control is to lower the output voltage when the load current is large and thereby reduce load power consumption. The LTM4650-2 example shows that the net power savings is 1.4W or 5.6%, which greatly saves power consumption and extends battery life. Series AVP Implementation AVP refers to the regulator output voltage regulated at a point that is dependent on the load current, while with the conventional approach (non-AVP) that voltage is fixed at nominal VOUT for all loads as shown in Figure 1. With the AVP approach, the output voltage drops gradually when the output current is increased. At light load, the output voltage is set to regulate to slightly higher than the nominal value, while at heavy load, the output voltage is set to regulate to slightly lower than the nominal value.1 When load current suddenly increases, the output voltage starts from a level higher than nominal so the output voltage can droop more and stay within the specified voltage range. When load current suddenly decreases, the output voltage starts at a level lower than nominal so the output voltage can have more overshoot and stay within the specified voltage range. The output voltage should be constrained within the specified voltage limits (between VMAX and VMIN) for all load current ranges. Figure 2 shows the AVP series compensation circuit. The internal LEFT: Figure 1. VOUT with AVP vs. the fixed nominal VOUT of a conventional approach (non-AVP). LEFT: Figure 2. AVP series compensation circuit.
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