Datasheet LT8620 (Analog Devices) - 10

LT8620
OPERATION
The LT8620 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 to clock cycle. Current in the inductor then increases until an external clock frequency and operate in pulse-skipping the top switch current comparator trips and turns off the mode. While in pulse-skipping mode the oscillator operates top power switch. The peak inductor current at which continuously and positive SW transitions are aligned to the top switch turns off is controlled by the voltage on the clock. During light loads, switch pulses are skipped the internal VC node. The error amplifier servos the VC to regulate the output and the quiescent current will be node by comparing the voltage on the VFB pin with an several hundred µA. internal 0.97V reference. When the load current increases To improve efficiency across all loads, supply current to it causes a reduction in the feedback voltage relative to internal circuitry can be sourced from the BIAS pin when the reference leading the error amplifier to raise the VC biased at 3.3V or above. Else, the internal circuitry will draw voltage until the average inductor current matches the new 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 LT8620 output is programmed at 3.3V or above. cycle begins or inductor current falls to zero. If overload Comparators monitoring the FB pin voltage will pull the conditions result in more than 3.9A flowing through the PG pin low if the output voltage varies more than ±9% bottom switch, the next clock cycle will be delayed until (typical) from the set point, or if a fault condition is present. switch current returns to a safe level. The oscillator reduces the LT8620’s operating frequency If the EN/UV pin is low, the LT8620 is shut down and when the voltage at the FB pin is low. This frequency draws 1µA from the input. When the EN/UV pin is above foldback helps to control the inductor current when the 1V, the switching regulator will become active. output voltage is lower than the programmed value which occurs during start-up or overcurrent conditions. When To optimize efficiency at light loads, the LT8620 operates a clock is applied to the SYNC pin or the SYNC pin is in Burst Mode operation in light load situations. Between held DC high, the frequency foldback is disabled and the bursts, all circuitry associated with controlling the output switching frequency will slow down only during overcur- switch is shut down, reducing the input supply current to rent conditions. 1.7μA. In a typical application, 2.5μA will be consumed 8620fa 10 For more information www.linear.com/LT8620 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts