National Semiconductor Corp. has introduced what it says is the industry's first emulated current-mode-controlled buck-boost DC-DC regulator-controller with an operating voltage range of 3 V to 75 V 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.

This LM5118 switching regulator features peak efficiency of 95 percent and its simple two-switch configuration enables design engineers to easily configure a complete power converter with ultra-wide input voltage range. Operation from below 3 V to 75 V 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 12.6 V battery, but with a weak battery during cold crank conditions, the battery voltage could fall down, momentarily, to 4 V. To ensure seamless control from electronic modules, the system must still operate at 4 V, or below.

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. This provides superior line and load transient response and low-duty cycle operation that is not achievable with traditional current-mode control. 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 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 is packaged in a 20-pin thermally enhanced TSSOP package.

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