Alongside the 42V LM25149-Q1 with the AEF active filter, the company has also integrated passive filters into another DC-DC converter, the LM25149. TI is also working on pin-to-pin compatible 80V versions of both devices.
The two also use a dual-random spread-spectrum (DRSS) technology, and the combination allows designers to reduce the area of the external EMI filter in half, lower the conducted EMI of the power design by as much as 55 dBµV across multiple frequency bands, or achieve a combination of reduced filter size and low EMI.
“This is the first buck controller with an integrated active EMI filter,” said Ganesh Srinivasan, product line manager for wide Vin buck switching regulators. “This is a breakthrough technology. The active EMI filter senses the noise at the input and feeds a signal out of phase to fully cancel it. With the active filter and DRSS it is also possible to get the same performance and reduce the size of the bulky EMI filters by 50 percent in area and 75 percent in volume,” he said.
“The AEF amplifier is configured to respond very quickly, to get attenuation up to a frequency of about 5 MHz,” said Srinivasan.
The active EMI filter with voltage sense and current cancellation (VSCC) uses an operational-amplifier (op-amp) circuit as a capacitive multiplier to replace the filter capacitor (CF) in the passive design. The active filter sensing, injection and compensation impedances use relatively low capacitance values with small component footprints to design a gain (G op). The effective active capacitance is set by the op-amp circuit gain and an injection capacitor (CINJ).
The AEF senses the noise voltage, amplifies it and injects a cancellation current into the system. Having a large gain creates a low-impedance path to shunt noise and the measured noise voltage across the load, making it possible to reduce the voltage noise
Depending on the gain and bandwidth of the active