LT8253EUFDM datasheet(8/20 Pages) AD

8 / 20 page

LT8253/LT8253A

Rev. 0

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OPERATION

(1) Peak-Buck in Buck Region (VIN >> VOUT)

When VIN is much higher than VOUT, the LT8253/LT8253A

use peak-buck current mode control in buck region

(Figure 2). Switch C is always off and switch D is always

on. At the beginning of every cycle, switch A is turned on

and the inductor current ramps up. When the inductor

current hits the peak buck current threshold commanded

by VC voltage at buck current comparator A3 during (A+D)

phase, switch A is turned off and switch B is turned on

for the rest of the cycle. Switches A and B will alternate,

behaving like a typical synchronous buck regulator.

100% OFF

100% ON

A+D

B+D

8253A F02

Figure 2. Peak-Buck in Buck Region (VIN >> VOUT)

(2) Peak-Buck in Buck-Boost Region (VIN ~> VOUT)

When VIN is slightly higher than VOUT, the LT8253/

LT8253A use peak-buck current mode control in buck-

boost region (Figure 3). Switch C is always turned on for

the beginning preset cycle and switch D is always turned

on for the remaining cycle. At the beginning of every

cycle, switches A and C are turned on and the inductor

current ramps up. After preset cycle, switch C is turned off

and switch D is turned on, and the inductor keeps ramping

up. When the inductor current hits the peak buck current

threshold commanded by VC voltage at buck current com-

parator A3 during (A+D) phase, switch A is turned off and

switch B is turned on for the rest of the cycle.

A+D

A+C

B+D

A+D

A+C

B+D

8253A F03

Figure 3. Peak-Buck in Buck-Boost Region (VIN ~> VOUT)

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