LT8686SJVPBF datasheet(16/26 Pages) AD

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LT8686S

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

COMBINING CHANNELS

The LT8686S provides the ability to combine multiple

regulators to create a single regulator capable of greater

output current using a single inductor.

The allowed channel combinations are given in Table 2.

Table 2. Allowed Channel Combinations

CONFIGURATION

NUMBER OF

INDEPENDENT REGULATORS

1, 2, 3, 4

1, 2, 3 + 4

1 + 2, 3, 4

1 + 2, 3 + 4

When combining, the lowest numbered channel assumes

control of the combined regulators. For example, with

channel 1 and channel 2 combined, channel 1 assumes

control (master) and channel 2 becomes depen-

dent (slave). A feedback network is connected only to

the master channel to program the combined regulator

output voltage. The slave channel’s feedback pin must be

connected to INTVCC.

Combined channels must have a low impedance connec-

tion between their respective VIN pins, SW pins, and BST

pins. Only a single inductor is connected to the com-

bined SW pins. Though combined channels’ BST pins

are connected together, each channel should retain their

individual boost capacitors.

A simplified application schematic showing sharing

between channels 1 and 2 as well as channels 3 and 4 is

given in Figure 3.

REVERSE INPUT PROTECTION

In some applications, such as battery charging or bat-

tery backup applications, an LT8686S channel output

may be held high when its input is made to either float

or is grounded.

VIN

BIAS

FB1

FB2

FB3

FB4

PG1

PG2

PG3

PG4

SYNC/MODE

VIN1

VIN2

EN/UVLO

EN2

BST1

BST2

BST3

TRK/SS1

TRK/SS2

TRK/SS3

TRK/SS4

SW1

SW2

SW3

LT8686S

3V TO

42V

VIN

VIN3

VIN4

EN3

EN4

3V TO

8686S F03

BST4

SW4

OUT1,2

OUT3,4

INTVCC

Figure 3. Simplified Schematic of Channel Sharing

If the input to the channel is floated, and the LT8686S is

enabled, then the LT8686S’s internal circuitry will pull

its quiescent current through the SW pin. If the input is

floated, and the LT8686S is disabled, then the SW pin

current will drop to less than 1µA. If the input is grounded,

an input protection diode is required to prevent reverse

current from the output, through the top power MOSFET

body diode (shown in the Block Diagram), out of the VINx

pin to the grounded input.

BUCK REGULATOR COMPONENT SELECTION

Setting the Output Voltages

The output voltages of the buck channels are set with a

resistor divider from the output to the related FBx pin as

shown in Figure 4.

FBx

SWx

LT8686S

CFF

(OPT)

COUT

8686S F04

OUT

Figure 4. Feedback Resistor Divider

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