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LTC1646

1646fa

Table 6. N-Channel Power MOSFET Selection Guide

CURRENT LEVEL (A)

PART NUMBER

DESCRIPTION

MANUFACTURER

0 to 2

MMDF3N02HD

Dual N-Channel SO-8

ON Semiconductor

RDS(ON) = 0.1Ω

2 to 5

MMSF5N02HD

Single N-Channel SO-8

ON Semiconductor

RDS(ON) = 0.025Ω

5 to 10

MTB50N06V

Single N-Channel DD Pak

ON Semiconductor

RDS(ON) = 0.028Ω

5 to 10

IRF7413

Single N-Channel SO-8

International Rectifier

RDS(ON) = 0.01Ω

5 to 10

Si4410DY

Single N-Channel SO-8

Vishay-Siliconix

RDS(ON) = 0.01Ω

Table 7. Sense Resistor Selection Guide

CURRENT LIMIT VALUE

PART NUMBER

DESCRIPTION

MANUFACTURER

LR120601R055F

0.055

Ω, 0.5W, 1% Resistor

IRC-TT

WSL1206R055

Vishay-Dale

LR120601R028F

0.028

Ω, 0.5W, 1% Resistor

IRC-TT

WSL1206R028

Vishay-Dale

LR120601R011F

0.011

Ω, 0.5W, 1% Resistor

IRC-TT

WSL2010R011

Vishay-Dale

7.6A

WSL2512R007

0.007

Ω, 1W, 1% Resistor

Vishay-Dale

10A

WSL2512R005

0.005

Ω, 1W, 1% Resistor

Vishay-Dale

PCB Layout Considerations

For proper operation of the LTC1646’s circuit breaker

function, a 4-wire Kelvin connection to the sense resistors

is highly recommended. A recommended PCB layout for

the sense resistor, the power MOSFET, and the GATE drive

components around the LTC1646 is illustrated in

Figure 15. In Hot Swap applications where load currents

can reach 10A, narrow PCB tracks exhibit more resistance

than wider tracks and operate at more elevated tempera-

tures. Since the sheet resistance of 1 ounce copper foil is

approximately 0.5m

Ω/■

■,trackresistancesaddupquickly

in high current applications. Thus, to keep PCB track

resistance and temperature rise to a minimum, the sug-

gested trace width in these applications for 1 ounce

copper foil is 0.03" for each ampere of DC current.

In the majority of applications, it will be necessary to use

plated-through vias to make circuit connections from

component layers to power and ground layers internal to

the PC board. For 1 ounce copper foil plating, a general rule

is 1A of DC current per via, making sure the via is properly

dimensioned so that solder completely fills any void. For

other plating thicknesses, check with your PCB fabrication

facility.

Power MOSFET and Sense Resistor Selection

Table 6 lists some current MOSFET transistors that are

available and Table 7 lists some current sense resistors

that can be used with the LTC1646’s circuit breakers.

Table 8 lists supplier web site addresses for discrete

component mentioned throughout the LTC1646 data sheet.

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