Buck Converter Uses Emulated-Current Mode
Feb 28, 2007 11:24 AM
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National Semiconductor’s LM5116 is a 6-V to 100-V current-mode buck controller utilizing emulated current-mode (ECM) technology to reduce noise sensitivity of the PWM circuit. The IC is well suited for stepdown regulator applications from a high-voltage or widely varying input supply.
The device has a programmable output range from 1.215 V to 80 V. 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 VIN-to-VOUT stepdown ratio of 20:1 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 µA of total input current. 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 LM5116 is available in a power-enhanced TSSOP-20 package featuring an exposed die-attach pad to aid thermal dissipation. Pricing is $3.25 in 1000-unit quantities. Evaluation boards and samples are also available.
