LT8210 datasheet(29/59 Pages) AD

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Data Sheet

LT8210-1

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Rev. A

29 of 59

Figure 51. Buck-Boost Region Switching Waveforms

Power Switch Control (Pass-Thru Mode)

In pass-thru mode, the buck and boost regulation loops function independently after start-up. Separate error amps

are used to create a pass-thru window by setting the output voltage for the buck regulation, VOUT(BUCK), higher than

the programmed output voltage for boost regulation, VOUT(BOOST). Figure 52 shows the switching regions in pass-thru

mode versus input voltage.

When VINP >> VOUT(BUCK), the LT8210-1 operates in the buck region. In this region, switch D is always on while switch C

is always off, switches A and B will toggle on and off, acting as a synchronous buck regulator with the output at

VOUT(BUCK). When VIN is between 93% to 119% of VOUT(BUCK), switch D will also begin switching to avoid the need for pulse

skipping. Switch C will alternate with D in this region. When VINP << VOUT(BOOST) switch A is always on while switch B is

always off, switches C and D toggle on and off, acting as a synchronous boost regulator to maintain the output at

VOUT(BOOST). When VIN is between 84% to 107% of VOUT(BOOST), switch A will also begin switching, alternating with switch

B. When VINP is between VOUT(BOOST)and VOUT(BUCK), the output voltage will track the input. Once VOUT has settled close to

VINP, the LT8210-1 will enter a low power state where switches A and D are turned on continuously and switches B

and C are off. In pass-thru mode, reverse current is handled in a similar manner to DCM while switching. In the non-

switching state, reverse-current is detected through direct comparison of the VINP and VOUTvoltages. If the voltage on

VOUT exceeds that on VINP by a set percentage, switches A, C, and D are turned off and the output is only reconnected

after it has discharged to be nearly equal to VINP. If a positive line transient occurs while in the non-switching pass-

thru window causing VINP to exceed VOUT by a set percentage, switching will recommence to prevent large amplitude

ringing in the inductor current. The output will be driven to the input voltage in a manner similar to soft-start and

switches A and D will turn on continuously again after VOUT settles close to VINP.

VINP – VOUT

–VOUT

VINP

A + D

A + C

B + D

A + D

LT8210 Datasheet(PDF) 29 Page - Analog Devices