LT8253EUFDM datasheet(9/20 Pages) AD

9 / 20 page

LT8253/LT8253A

Rev. 0

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(3) Peak-Boost in Buck-Boost Region (VIN <~ VOUT)

When VIN is slightly lower than VOUT, the LT8253/

LT8253A use peak-boost current mode control in buck-

boost region (Figure 4). Switch A is always turned on

for the beginning preset cycle and switch B is always

turned on for the remaining cycle. At the beginning of

every cycle, switches A and C are turned on and the induc-

tor current ramps up. When the inductor current hits the

peak boost current threshold commanded by VC voltage at

boost current comparator A4 during (A+C) phase, switch

C is turned off and switch D is turned on for the rest of the

cycle. After preset cycle, 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 F04

Figure 4. Peak-Boost in Buck-Boost Region (VIN <~ VOUT)

OPERATION

(4) Peak-Boost in Boost Region (VIN << VOUT)

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

use peak-boost current mode control in boost region

(Figure 5). Switch A is always on and switch B is always

off. At the beginning of every cycle, switch C is turned

on and the inductor current ramps up. When the induc-

tor current hits the peak boost current threshold com-

manded by VC voltage at boost current comparator A4

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

is turned on for the rest of the cycle. Switches C and D

will alternate, behaving like a typical synchronous boost

regulator.

100% ON

100% OFF

A+D

A+C

A+D

A+C

8253A F05

Figure 5. Peak-Boost in Boost Region (VIN << VOUT)

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