DC2457A: 12V @ 4A, 4 ~ 60V in, Buck-Boost

Demonstration circuit DC2457A is a 12V, 4A, 4-switch synchronous buck-boost regulator featuring low EMI noise and small footprint. It runs at 400kHz switching frequency. Spread spectrum frequency modulation (SSFM) can be turned on with a simple jumper, reducing EMI. DC2457A also comes with other low EMI features including optimized layout, input and output filters. It passes CISPR 25 class 5 conducted and radiated EMI.

The operating input voltage range of DC2457A is from 4V to 60V. The output voltage and EN/UVLO, are all programmed by resistor dividers. EN/UVLO is set so the circuit will turn off when the input voltage falls below 4V and will turn on when the input voltage rises above 5V.

The CTRL input is pulled up to the VREF pin through a 0Ω resistor to set the output current limit to its maximum, and an external voltage on CTRL can be used to lower the current limit if the resistor is removed. A capacitor at the SS pin programs soft-start.

The PGOOD is status flag indicates when output voltage is within ±10% of final regulation voltage. The LT8390's proprietary peak current mode buck-boost architecture ensures DC2457A runs either in discontinuous conduction mode (DCM) or pulse-skipping mode (PSM) without reversed inductor current. Both of them enhance the light load efficiency.

To improve the EMI performance, the LT8390 has spread spectrum frequency modulation. With the SYNC/SPRD pin tied to INTVCC, LT8390 starts to spread its switching frequency ±15% around the programmed oscillator frequency. There is an EMI filter on the input of DC2457A. There is also a small ferrite bead output filter. These filters, combined with proper board layout and SSFM are effective to help the circuit pass CISPR 25 class 5 conducted and radiated EMI. Please follow the recommended layout and four-layer thickness of DC2457A for low EMI applications.

The LT8390 data sheet must be read in conjunction with this demo manual to properly use or modify demo circuit DC2457A.