Texas Instruments Debuts DC/DC Controllers With Active EMI FiltersApril 15, 2021 by Gary Elinoff
The new family of buck controllers also features dual-random spread-spectrum (DRSS) technology for the smallest-sized EMI control.
Texas Instruments’ (TI) LM25149-Q1 and LM25149 enable designers to lower the conducted EMI of the power design by as much as 55 dBµV across multiple frequency bands while cutting in half the board space occupied by the external EMI filter.
The LM25149-Q1 and LM25149. Image courtesy of TI
TI describes the new devices as the industry’s first DC/DC controller that includes an integrated, built-in EMI filter. Through this agency, the devices enable designers to drastically cut down on the space, weight and cost that must be devoted to EMI control.
The LM25149 accepts input power over a range of 3.5 to 42 volts. Output range is adjustable over a 0.8 to 36-volt range, or alternatively, at fixed outputs of 3.3, 5, or 12 volts with 1% accuracy.
The maximum output current is 30 amps. The typical quiescent current is 9.5 µA, and the shutdown mode current is 2.2 µA. The device’s switching frequency range is from 100 kHz to 2.2 MHz.
More specific information on the LM25149-Q1can be found here.
The Importance of Reducing Power Supply EMI
With ever more electronic circuitry packed into ever less space in both EVs and conventionally powered vehicles, EMI specifications are, by necessity, becoming tougher and tougher. Passive, external EMI filters, with necessarily large capacitors and inductors, will inevitably take up critical board space and add to overall power system weight, two extremely undesirable outcomes.
To avoid this pitfall, the LM25149 employs active EMI filter (AEF) and DRSS technology. AEF will detect any noise or ripple voltage on the DC input bus and then inject an out-of-phase cancellation signal to reduce the ripple or noise voltage. DRSS combines a low-frequency triangular and high-frequency random modulation, which serves to optimize EMI reduction in both the high-frequency and low-frequency radio frequency bands.
Image courtesy of Texas Instruments.
The combined effects of active the AEF and DRSS, as per TI, reduces the EMI to the point that the size of the external EMI can be reduced by 50%, saving precious board space and weight. TI provides further information in a technical article and in a white paper.
Meeting CISPR 25
As per TI, CISPR 25 Class 5 is the automotive industry’s toughest standard for automotive EMI. The new buck controllers will enable designers to meet that standard by controlling EMI occurring across the frequency bands that are part of the Class 5 frequency spectrum
The internal AEF detects and combats EMI in the low frequency 150 kHz to 10 MHz bands. At a switching frequency of 440 kHz, the AEF provides as much as 50 dBµV EMI attenuation. When compared to a typical passive filter arrangement, an improvement of 20 dBµV is affected.
DRSS technology adds another 5 dBµV across both the above-mentioned low and high-frequency bands.
The LM25149 operates over a temperature range of -40 to 150℃
It is available in a 3.5 by 5.5 mm VQFN (24) package with wettable flanks for easy optical inspection
Electrostatic discharge rating is ±2000 and ±750 volts as per the Human body model (HBM) and the charged device model (CDM), respectively.
Getting to Market Faster
The LM25149-Q1EVM-2100 evaluation module (EVM) is designed to demonstrate the LM25149-Q1 automotive synchronous DC/DC buck controller.
The LM25149-Q1EVM-2100 EVM. Image courtesy of TI
It operates over a 5.5 to 36-volt input voltage range and delivers a fixed 5-volt output. Setpoint accuracy is to within 1% setpoint accuracy. The output current is as high as 8 amps.