National said the device is suited for step-down regulator applications from a high-voltage or widely varying input supply. Current-mode control based on patented emulated current-mode (ECM) technology is said to reduce the noise sensitivity of the pulse-width modulation (PWM) circuit and enable reliable control of very small duty cycles in high input voltage applications. Additional features include thermal shutdown, programmable soft-start, frequency synchronization, cycle-by-cycle current limit and adjustable line undervoltage lockout (UVLO).
National said its ECM control overcomes the noise susceptibility and duty cycle limitations of traditional peak current-mode control by emulating the buck switch current signal that 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, according to the company.
The LM5116 features an input range up to 100 V and a programmable output range from 1.215 V to 80 V. 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 10 µA 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 LM5116 is available in a power-enhanced TSSOP-20 package featuring an exposed die attach pad to aid thermal dissipation.