National Semi Introduces Emulated Current-Mode-Controlled Buck-Boost DC-DC Regulator Controller
National Semiconductor Corp. introduced what it describes as the industry’s first emulated current-mode-controlled buck-boost dc-dc regulator controller with a "best-in- class" operating voltage range of 3 to 75V for automotive, telecommunications and battery-powered systems. The LM5118 features programmable switching frequency up to 500 kHz, ultra-low shutdown current and smooth transition between buck and buck-boost modes. The LM5118 switching regulator features peak efficiency of 95%, positioning it among National’s PowerWise® family of energy-efficient products.
The simple two-switch configuration is said to enable design engineers to easily assemble a complete power converter with ultra-wide input voltage range. Operation below 3 to 75V makes the LM5118 well-suited for automotive applications such as powering the dashboard display, electronic controls such as anti-lock braking or fuel injection control, and the multitude of microcontrollers used in today’s cars. These systems operate from a 12.6V battery, but with a weak battery during cold crank conditions, the battery voltage could fall momentarily down to 4V. To ensure seamless control from electronic modules, the system must still operate at 4V or below. It is claimed that the unique buck-boost control of the LM5118 makes this seamless control possible.
The control method of the LM5118 is based upon current-mode control utilizing an emulated current ramp. The patented emulated current-mode control technology provides superior line and load transient response and low duty cycle operation that is not achievable with traditional current-mode control.
National’s LM5118 switching regulator features all of the functions necessary to implement an efficient buck-boost regulator, using a minimum of external components. The buck-boost topology maintains output voltage regulation when the input voltage is either less than or greater than the output voltage, making the product especially suitable for automotive applications.
The LM5118 operates as a buck regulator when the input voltage is sufficiently greater than the regulated output voltage and gradually transitions to the buck-boost mode as the input voltage approaches the output. This dual-mode approach maintains regulation over a wide range of input voltages with optimal conversion efficiency in the buck mode and a glitch-free output during mode transitions. The LM5118 includes drivers for the high-side buck MOSFET and the low-side boost MOSFET. The emulated current-mode control reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable control of very small duty cycles necessary in high-input voltage applications. Additional protection features include current limit, thermal shutdown and an enable input.
The LM5118 is offered in a 20-pin thermally enhanced TSSOP package. Available now, the LM5118 is priced at $2.92 each in 1,000-unit quantities.
