LT8350RVPBF datasheet(11/24 Pages) AD

11 / 24 page

LT8350

Rev. 0

For more information www.analog.com

OPERATION

The LT8350 is a current mode DC/DC converter that can

regulate output voltage from input voltage above, below,

or equal to the output voltage. Four internal low resistance

N-channel DMOS switches minimize the size of the

application circuit and reduce power losses to maximize

efficiency. Internal high side gate drivers, further simplify

the design process. The ADI proprietary peak current

mode control scheme directly senses the inductor current

across the internal power switches and provides smooth

transition between buck region, buck-boost region, and

boost region. The LT8350 can be configured to operate

over a wide range of switching frequencies, from 200kHz

to 2MHz, allowing applications to be optimized for broad

area and efficiency. The operation can be best understood

by referring to the Block Diagram.

Power Switch Control

Figure 1 shows the topology of the LT8350 power stage

which is comprised of four N-channel DMOS switches and

their associated gate drivers. Figure 2 shows the current

mode control as a function of VIN/VOUT ratio and Figure 3

shows the operation region as a function of VIN/VOUT ratio.

The power switches are properly controlled to smoothly

transition between modes and regions. Hysteresis is

added to prevent chattering between modes and regions.

Figure 1. Power Stage Schematic

Figure 2. Current Mode vs VIN/VOUT Ratio

Figure 3. Operation Region vs VIN/VOUT Ratio

VIN/VOUT

BUCK

BUCK-BOOST

BOOST

1.25

(1)

(2)

(3)

(4)

0.85

0.75

8350 F03

1.33

VIN/VOUT

PEAK-BUCK

PEAK-BOOST

0.98

8350 F02

1.02

BST1

BST2

CBST1

CBST2

LT8350

INTVCC

VIN

SW1

SW2

INTVCC

8350 F01

GND

VOUT

There are total four states: (1) peak-buck current mode

control in buck region, (2) peak-buck current mode con-

trol in buck-boost region, (3) peak-boost current mode

control in buck-boost region, and (4) peak-boost current

mode control in boost region. The following sections

give detailed description for each state with waveforms,

in which the shoot-through protection dead time between

switches A and B, between switches C and D are ignored

for simplification.

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