Top Stories Industry’s First 100V Current-Mode Buck Controller LM5116 Synchronous Buck Controller Features Patented Emulated Current-Mode Control for High Step-Down Ratios National Semiconductor Corporation has released the new LM5116, the industry’s first 6V to 100V current-mode buck controller for use in telecommunications, automotive and industrial control applications. The LM5116 features a unique combination of high performance, flexibility and ease-of-use for DC-DC power supply designs. The device joins National’s portfolio of synchronous buck controllers, offering extended input voltage range and load current capability. The LM5116 is well-suited for step-down regulator applications from a high voltage or widely varying input supply. The current mode control utilizing National’s patented emulated current-mode (ECM) technology reduces noise sensitivity of the pulse-width modulation (PWM) circuit. It enables reliable control of very small duty cycles necessary in high input voltage applications. Additional features include thermal shutdown, programmable soft-start, frequency synchronization, cycle-by-cycle current limit and adjustable line under voltage lockout (UVLO). About Emulated Current-Mode Technology Emulated current-mode control overcomes the noise susceptibility and duty cycle limitations of traditional peak current-mode control by emulating the buck switch current signal, which is used for pulse-width modulation. The emulated current signal is developed by charging a capacitor with controlled currents that produce a capacitor voltage waveform directly proportional to the current in the buck switch. Developing the current signal for the PWM without directly measuring the buck switch current minimizes the effect of switching noise, while maintaining the benefits of the current-mode control. Technical Features of the LM5116 Buck Controller The LM5116 has an ultra-wide input range up to 100V, with a programmable output range from 1.215V to 80V. The reduced noise sensitivity of the PWM control circuit allows reliable operation with very small duty cycles necessary in high input voltage applications. The emulated current ramp enables the LM5116 to exceed a 20:1 Vin:Vout step-down ratio when operating at 500 kHz. The operating frequency is user-programmable up to 1 MHz with the capability to synchronize switching to an external clock signal. A low quiescent-current sleep mode disables the controller and consumes only 10 microamps of total input current for minimal off-state drain in battery-powered applications. A user-selectable diode emulation mode enables discontinuous inductor current operation at light load conditions for improved efficiency. Controlled start up into a pre-biased load is achieved by gradually disabling the diode emulation of the synchronous MOSFET. The programmable soft-start, input UVLO and voltage tracking features further enhance the system designer’s control of the turn-on transition. The company's Web site address is http://www.national.com/. [Reprinted with kind permission from National Semiconductor]

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