Data Sheet

LT8350S

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Rev. A

21 of 36

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

When VIN is slightly higher than VOUT, the LT8350S uses peak-buck current mode control in the buck-boost region (See

Figure 32). In each switching cycle, switch C is turned on for the beginning 20% of the cycle and switch D is turned on

for the remaining 80% of the cycle. At the beginning of every cycle, switches A and C are turned on and the inductor

current ramps up. After a 20% cycle, switch C is turned off, 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

comparator A1 during the (A + D) phase, switch A is turned off and switch B is turned on for the rest of the cycle.

Figure 32. Peak-Buck in Buck-Boost Region (VIN~>VOUT)

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

When VIN is slightly lower than VOUT, the LT8350S uses peak-boost current mode control in the buck-boost region (See

Figure 33). In each switching cycle, switch A is turned on for the beginning 80% of the cycle and switch B is turned on

for the remaining 20% of the 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 A2 during the (A + C) phase, switch C is turned off, and switch D is turned on for the rest of

the cycle. After the 80% cycle, switch A is turned off and switch B is turned on for the rest of the cycle.

Figure 33. Peak-Boost in Buck-Boost Region (VIN<~VOUT)

A + C

B + D

A

B

C

D

IL

20%

20%

80%

80%

A + D

A + C

B + D

A + D