LT8302MPS8E 查看數據表（PDF） - Linear Technology

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LT8302MPS8E

42VIN Micropower No-Opto Isolated Flyback Converter with 65V/3.6A Switch

Linear Technology 

LT8302

Operation

Boundary conduction mode returns the secondary current

to zero every cycle, so parasitic resistive voltage drops

do not cause load regulation errors. Boundary conduc-

tion mode also allows the use of smaller transformers

compared to continuous conduction mode and does not

exhibit subharmonic oscillation.

Discontinuous Conduction Mode Operation

As the load gets lighter, boundary conduction mode in-

creases the switching frequency and decreases the switch

peak current at the same ratio. Running at a higher switching

frequency up to several MHz increases switching and gate

charge losses. To avoid this scenario, the LT8302 has an

additional internal oscillator, which clamps the maximum

switching frequency to be less than 380kHz. Once the

switching frequency hits the internal frequency clamp,

the part starts to delay the switch turn-on and operates

in discontinuous conduction mode.

Low Ripple Burst Mode Operation

Unlike traditional flyback converters, the LT8302 has to

turn on and off at least for a minimum amount of time

and with a minimum frequency to allow accurate sampling

of the output voltage. The inherent minimum switch cur-

rent limit and minimum switch-off time are necessary to

guarantee the correct operation of specific applications.

As the load gets very light, the LT8302 starts to fold back

the switching frequency while keeping the minimum switch

current limit. So the load current is able to decrease while

still allowing minimum switch-off time for the sample-and-

hold error amplifier. Meanwhile, the part switches between

sleep mode and active mode, thereby reducing the effec-

tive quiescent current to improve light load efficiency. In

this condition, the LT8302 runs in low ripple Burst Mode

operation. The typical 12kHz minimum switching frequency

determines how often the output voltage is sampled and

also the minimum load requirement.

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For more information www.linear.com/LT8302

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