LT3757 datasheet(13/28 Pages) AD

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LT8392

Rev. 0

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

When VIN is slightly lower than VOUT, the LT8392 uses

peak-boost current mode control in buck-boost region

(Figure 6). Switch A is always turned on for the begin-

ning 85% cycle and switch B is always turned on for the

remaining 15% cycle. At the beginning of every cycle,

switches A and C are turned on and the inductor 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 85% cycle, switch A is turned off and switch

B is turned on for the rest of the cycle.

OPERATION

Figure 6. Peak-Boost in Buck-Boost Region (VIN <~ VOUT)

Figure 7. Peak-Boost in Boost Region (VIN << VOUT)

15%

85%

15%

A+D

A+C

B+D

A+D

A+C

B+D

8392 F06

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

When VIN is much lower than VOUT, the LT8392 uses peak-

boost current mode control in boost region (Figure 7).

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 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. 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

8392 F07

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