LT8331 datasheet(11/34 Pages) AD

11 / 34 page

LT8357

Rev. 0

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OPERATION

When VOUT is very low during start-up or a short-circuit

fault on the output, the switching regulator must operate

at low duty cycle to maintain the power switch current

within the current limit range, since the inductor current

decay rate is very low during switch off time. The mini-

mum on-time limitation may prevent the switcher from

attaining a sufficiently low duty cycle at the programmed

switching frequency. Therefore, the switch current will

keep increasing through each switch cycle, exceed-

ing the programmed current limit. To prevent the peak

switch current from exceeding the programmed limit,

the LT8357 implements a frequency foldback function,

which starts to fold back the switching frequency as the

FB voltage drops below 75% of its regulation voltage

(see the Normalized Oscillator Frequency vs FB Voltage

in the Typical Performance Characteristics section). The

frequency foldback function prevents the inductor cur-

rent from exceeding the programmed limit because of

the minimum on-time. Once the frequency is folded back,

external clock synchronization, Burst Mode operation and

spread spectrum frequency modulation are all disabled to

prevent interference to the frequency foldback operation.

LT8331 Datasheet(PDF) 11 Page - Analog Devices