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LT8390

8390fa

For more information www.linear.com/LT8390

OPERATION

The LT8390 is a current mode DC/DC controller that can

regulate output voltage, input or output current from in-

put voltage above, below, or equal to the output voltage.

The LTC proprietary peak-buck peak-boost current mode

control scheme uses a single inductor current sense resis-

tor and provides smooth transition between buck region,

buck-boost region, and boost region. Its operation is best

understood by referring to the Block Diagram.

Power Switch Control

Figure 1 shows a simplified diagram of how the four power

switches A, B, C, and D are connected to the inductor L,

the current sense resistor RSENSE, power input VIN, power

outputVOUT,andground.ThecurrentsenseresistorRSENSE

connected to the LSP and LSN pins provides inductor

current information for both peak current mode control

and reverse current detection in buck region, buck-boost

region,andboostregion.Figure2showsthecurrentmode

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

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

powerswitchesareproperlycontrolledtosmoothlytransi-

tion between modes and regions. Hysteresis is added to

prevent chattering between modes and regions.

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.

Figure 1. Simplified Diagram of the Power Switches

Figure 2. Current Mode vs VIN/VOUT Ratio

Figure 3. Operation Region vs VIN/VOUT Ratio

VOUT

SW1

SW2

TG2

BG2

8390 F01

TG1

BG1

VIN

RSENSE

PEAK-BUCK

PEAK-BOOST

VIN/VOUT

0.98 1.00 1.02

8390 F02

BUCK

(1)

(2)

(3)

BOOST

BUCK-BOOST

VIN/VOUT

0.85

0.75

1.00

1.18

1.33

8390 F03

(4)

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