5V to 80V, 20A synchronous step-down converter with integrated GaN FETs for ultra-high efficiency

The LMG708B0 is a

GaN synchronous buck DC/DC converter offered from a family of devices that provide

ultra-high current density and excellent power conversion efficiency. The integrated low

RDS(on) GaN FETs with near-zero deadtime switching performance enable up to 20A

of output current across a wide input voltage range of 5V to 80V.

Phase stackable with synchronized

interleaving, the peak current-mode architecture of

the LMG708B0 supports accurate current sharing with paralleled

phases for even higher output current. Along with constant-voltage (CV) operation, a

dual-loop architecture with shared compensation provides constant-current (CC) regulation

for battery charging and other current-source type loads. This cohesive approach enables a

seamless transition between CV and CC modes, and high accuracy for voltage (±1%) and current

(±4.5%) regulation, effectively reducing the bill-of-materials (BOM) cost for applications

that require average output current control. VSET and ISET inputs facilitate dynamic

adjustment of the respective CV and CC loop setpoints, and an IMON output provides average

output current monitoring.

The LMG708B0 has a

thermally enhanced package (TEP) with optional top-side cooling (TSC) through exposed

package connections and low package parasitic

inductance for quiet switching performance.

A high-side

switch minimum on-time of 25ns facilitates large step-down ratios, enabling the direct

conversion from 24V or 48V inputs to

low-voltage rails for reduced system design cost and complexity. The LMG708B0 continues to operate during input voltage dips as low as 5V, at close to

100% duty cycle if needed. The 20µA sleep quiescent current with the output voltage in

regulation extends operating run-time in battery-powered systems.

The LMG708B0 includes several features to simplify compliance with CISPR 11 and CISPR 32 conducted emissions requirements.

Predictably timed GaN FET gate drivers along with integrated bootstrap switch and capacitor

minimize deadtime during switching transitions, reducing switching losses and improving EMI

performance at high input voltage and high switching frequency. To reduce input capacitor

ripple current and EMI filter size, interleaved operation using a SYNCOUT signal with

programmable phase shift works well for cascaded, multichannel or multiphase designs.

Resistor-adjustable switching frequency as high as 2.2MHz can be synchronized to an external

clock source up to 2.64MHz to eliminate beat frequencies in noise-sensitive applications.

Finally, the LMG708B0 has dual-random spread spectrum (DRSS), a

unique EMI-reduction feature that combines low-frequency triangular and high-frequency

random modulations to mitigate EMI disturbances across lower and higher frequency bands,

respectively.

Additional

features of the LMG708B0 include 125°C maximum junction temperature

operation, user-selectable PFM mode for lower current consumption during light-load

conditions, integrated bootstrap capacitor with synchronous charging for robust level

shifting, open-drain power-good (PG) indicator for fault reporting and output monitoring,

precision enable input for input UVLO, monotonic start-up into prebiased loads, dual-input

VCC bias subregulator, 30mV full-scale current sensing, hiccup-mode overload protection, and

thermal shutdown protection with automatic recovery for the controller.

The LMG708B0

comes in a 4.5mm × 6mm, thermally enhanced, 22-pin eQFN package using a flip-chip routable leadframe (FCRLF) packaging

technique. Leveraging high-performance GaN power FETs

(based on TI’s proprietary GaN IC technology), thermal management and EMI mitigation

features, CC/CV operation, and small design size, the LMG708B0

represents an excellent point-of-load regulator choice for applications requiring the most

efficient GaN design with useable current, lifetime reliability, and cost advantages.