Datasheet LT8614 (Analog Devices) - 11

LT8614
OPERATION
The LT8614 is a monolithic, constant frequency, current from the input supply when regulating with no load. The mode step-down DC/DC converter. An oscillator, with SYNC pin is tied low to use Burst Mode operation and can frequency set using a resistor on the RT pin, turns on be tied to a logic high to use pulse-skipping mode. If a the internal top power switch at the beginning of each clock is applied to the SYNC pin the part will synchronize clock cycle. Current in the inductor then increases until to an external clock frequency and operate in pulse-skip- the top switch current comparator trips and turns off the ping mode. While in pulse-skipping mode the oscillator top power switch. The peak inductor current at which the operates continuously and positive SW transitions are top switch turns off is controlled by the voltage on the aligned to the clock. During light loads, switch pulses are internal VC node. The error amplifier servos the VC node skipped to regulate the output and the quiescent current by comparing the voltage on the VFB pin with an inter- will be several hundred µA. nal 0.97V reference. When the load current increases it To improve efficiency across all loads, supply current to causes a reduction in the feedback voltage relative to the internal circuitry can be sourced from the BIAS pin when reference leading the error amplifier to raise the VC volt- biased at 3.3V or above. Else, the internal circuitry will age until the average inductor current matches the new draw current from V load current. When the top power switch turns off, the IN. The BIAS pin should be connected to V synchronous power switch turns on until the next clock OUT if the LT8614 output is programmed at 3.3V or above. cycle begins or inductor current falls to zero. If overload conditions result in more than 6.9A flowing through the Comparators monitoring the FB pin voltage wil pul the PG bottom switch, the next clock cycle will be delayed until pin low if the output voltage varies more than ±9% (typi- switch current returns to a safe level. cal) from the set point, or if a fault condition is present. If the EN/UV pin is low, the LT8614 is shut down and The oscillator reduces the LT8614’s operating frequency draws 1µA from the input. When the EN/UV pin is above when the voltage at the FB pin is low. This frequency 1V, the switching regulator will become active. foldback helps to control the inductor current when the output voltage is lower than the programmed value which To optimize efficiency at light loads, the LT8614 operates occurs during start-up or overcurrent conditions. When in Burst Mode operation in light load situations. Between a clock is applied to the SYNC pin or the SYNC pin is bursts, all circuitry associated with controlling the output held DC high, the frequency foldback is disabled and the switch is shut down, reducing the input supply current to switching frequency will slow down only during overcur- 1.7μA. In a typical application, 2.5μA will be consumed rent conditions. Rev. E For more information www.analog.com 11 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Applications Related Parts