LTC7890/LTC7891 DC/DC Switching Regulator Controller

ADI's LTC7890 and LTC7891 are high-performance, dual step-down, DC/DC switching regulator controllers that drive all N-channel synchronous gallium nitride (GaN) field effect transistor (FET) power stages from input voltages up to 100 V. They solve many of the challenges traditionally faced when using GaN FETs. The LTC7890 and LTC7891 simplify the application design, requiring no protection diodes or additional external components compared to a silicon metal oxide semiconductor field effect transistor (MOSFET) solution.

The internal smart bootstrap switches prevent overcharging of the BOOSTx pin to the SWx pin high-side driver supplies during dead times, protecting the gate of the top GaN FET. The LTC7890 and LTC7891 internally optimize the gate driver timing on both switching edges to achieve smart near-zero dead times, significantly improving efficiency and allowing for high-frequency operation, even at high input voltages. Alternatively, the user can adjust the dead times with external resistors for margin or to tailor the application.

The gate drive voltage of the LTC7890 and LTC7891 can be precisely adjusted from 4 V to 5.5 V to optimize performance and to allow the use of different GaN FETs or even logic-level MOSFETs.

Demonstration circuit DC2938A is a dual output non-isolated synchronous step-down converter that drives all N-channel GaN FET power stages. DC2938A features the LTC7890, a low quiescent current high frequency (programmable fixed frequency from 100 kHz up to 3 MHz) dual step-down DC/DC synchronous controller, with dedicated driver feature for GaN FET housed in a small 6 mm × 6 mm QFN package.

Demonstration circuit DC2995A is a buck regulator featuring the LTC7891. The DC2995A operates from a 36 V to 72 V input voltage range, generating a 12 V, 20 A output. The LTC7891 has a precision voltage reference, which can generate an output voltage with 2% tolerance over the full operating conditions. The 500 kHz switching frequency operation results in a small and efficient circuit. The converter achieves over 96% efficiency with 20 A load.