LTC4216IDE datasheet(17/24 Pages) LINER

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LTC4216

4216f

For example, if ILOAD(MAX) = 5A, RSENSE = 4.3mΩ. The

nearest standard value is 4mΩ.

For proper circuit breaker operation, kelvin-sense PCB

connections between the sense resistor and the LTC4216’s

SENSEP and SENSEN pins are strongly recommended.

Figure 12 illustrates the correct way of making connections

between the LTC4216 and the sense resistor. PCB layout

should be balanced and symmetrical to minimize wiring

errors. In addition, the PCB layout for the sense resistor

should include good thermal management techniques for

optimal sense resistor power dissipation.

The power rating of the sense resistor should accom-

modate the fault current level during analog current limit

so that the component is not damaged before the circuit

breaker trips.

Circuit Breaker Trip Current Calculation

For a selected RSENSE value, the typical load current that

trips the circuit breaker is given by:

TRIP TYP

CB TH TYP

SENSE TYP

()

)

()

∆

(13)

The minimum load current that trips the circuit breaker

is given by:

TRIP MIN

CB TH MIN

SENSE MAX

()

)

()

∆

21 5

(14)

Figure 12. Making PCB Connections to the Sense Resistor

SENSEP

SENSEN

TRACK WIDTH W:

0.03˝ PER AMPERE

ON 1OZ COPPER

CURRENT FLOW

TO LOAD

SENSE RESISTOR

CURRENT FLOW

TO LOAD

4216 F12

where

SENSE MAX

SENSE TYP

TOL

()

(

) •

⎛

⎝⎜

⎞

⎠⎟

100

The maximum load current that trips the circuit breaker

is given by:

TRIP MAX

CB TH MAX

SENSE MIN

()

)

()

∆

28 5

where

(15)

SENSE MIN

SENSE TYP

TOL

()

(

) •–

⎛

⎝⎜

⎞

⎠⎟

100

For example, if a sense resistor of 4mΩ ± 1% RTOL is used

for current sensing, the typical trip current, ITRIP(TYP) =

6.25A. From Equations (14) and (15), ITRIP(MIN) = 5.3A

and ITRIP(MAX) = 7.2A respectively.

For proper operation and to avoid tripping the circuit breaker

unnecessarily, the minimum trip current, ITRIP(MIN), must

exceed the maximum operating load current of the circuit

connected to the output of the MOSFET.

MOSFET Selection

The external MOSFET switch must have adequate safe

operating area (SOA) to handle short-circuit conditions

before the circuit breaker trips. These considerations

take precedence over continuous drain current ratings. A

MOSFET with adequate SOA for a given application can

always handle the required drain current, but the opposite

may not be true. Consult the manufacturer’s MOSFET

datasheet for safe operating area and effective transient

thermal impedance curves.

MOSFET selection is a 3-step process by assuming the

absence of a soft-start capacitor. First, RSENSE is chosen

and then the time required to charge the load capacitance

is determined. This timing, along with the maximum short-

circuit current and maximum load supply voltage, deﬁnes

an operating point that is checked against the MOSFET’s

SOA curve.

In addition, consider three other key parameters:

APPLICATIO S I FOR ATIO

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