DC1832A: 3.3V @ 3A, 4.3 ~ 60V in, Buck

Demonstration circuit 1832A is a monolithic step-down DC/DC switching regulator featuring the LT3995. The LT3995 is a compact, high efficiency monolithic step-down switching regulator that consumes only 2.7μA of quiescent current. The demo circuit is designed for 3.3V, 3A output from a 4.3V to 60V input. The switching frequency can be programmed either via oscillator resistor or external clock up to 2MHz. To synchronize to an external clock, move JP2 to SYNC and apply the external clock to the SYNC turret. The RT resistor (R5) should be chosen to set the LT3995 internal switching frequency at least 20% below the lowest synchronization input frequency.

Low ripple Burst Mode® operation increases the efficiency at the light load while keeping the output ripple below 15mV. The SYNC pin on the demo board is grounded by default by setting JP2 at RT FREQ for low ripple Burst Mode operation. Figure 1 shows the demo board efficiency at 12V input voltage.

The LT3995 is in shutdown when the EN pin is low and active when the pin is high. The threshold of the EN pin is accurate at 1.02V with 60mV of hysteresis. Users can populate R7 and R8 to provide a programmable under voltage lockout. A low dropout voltage of 500mV is maintained when the input voltage drops below the programmed output voltage. During a short-circuit fault, the LT3995 has current limit foldback to limit the power dissipation.

The demo board has an EMI filter installed. The EMI performance of the demo board at 12V input voltage is shown on Figure 2. The limit in Figure 2 is EN55022 Class B. The figure shows the circuit passes the test with a wide margin. To use the EMI filter, the input should be tied to VEMI not VIN.

The LT3995 data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this demo manual for demo circuit 1832A. The LT3995 is assembled in a 16-lead plastic MSOP package with an exposed pad for low thermal resistance. Proper board layout is essential for both proper operation and maximum thermal performance. See the data sheet sections for details.