Datasheet LT8604 (Analog Devices) - 10

link to page 9 LT8604
OPERATION
The LT8604 is a monolithic constant-frequency current associated with controlling the output switch is shut down mode step-down DC/DC converter. Operation is best reducing the input supply current to 1.7µA. In a typical understood by referring to the Block Diagram. An internal application with a 24V input, 2.5µA will be consumed from oscillator turns on the integrated top power switch at the the input supply when regulating with no load. beginning of each clock cycle. Current in the inductor then To improve efficiency across all loads, supply current to increases until the top switch current comparator trips internal circuitry can be sourced from the BIAS pin when and turns off the top power switch. The peak inductor cur- biased at 3.2V or above. Else, the internal circuitry will rent at which the top switch turns off is controlled by the draw current from V voltage on the internal V IN. The BIAS pin should be connected C node. The error amplifier servos to V the V OUT if the LT8604 output is programmed to a voltage C node by comparing the voltage on the FB pin with between 3.3V and 25V. an internal reference. When the load current increases, it causes a reduction in the feedback voltage relative to the Comparators monitoring the FB pin voltage wil pul the PG reference leading the error amplifier to raise the V pin low if the output voltage varies more than ±7.5% (typi- C volt- age until the average inductor current matches the new cal) from the set point, or if a fault condition is present. load current. When the top power switch turns off, the In the LT8604, the oscillator reduces its operating fre- synchronous power switch turns on until the next clock quency when the voltage at the FB pin is low. This fre- cycle begins or inductor current falls to zero. If overload quency foldback helps to control the inductor current conditions result in excess current flowing through the when the output voltage is lower than the programmed bottom switch, the next clock cycle will be delayed until value which occurs during start-up. switch current returns to a safe level. If the EN/UV pin is low, the LT8604 is shut down and To optimize efficiency, the LT8604 enters Burst Mode draws 1µA from the input. When the EN/UV pin is above operation at light loads. Between bursts, all circuitry 1.05V, the switching regulator becomes active. Rev. 0 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts