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LTC4213

4213f

APPLICATIO S I FOR ATIO

Figure 2. Short Circuit Fault Timing Diagram

CB TRIPS

∆VSENSE

VGATE

VCB

>VCB

VREADY

CIRCUIT BREAKER TRIPS

GATE AND READY PINS PULL LOW

SHORT CIRCUIT

tFAULT

4213 F02

The maximum load limit current is given by:

LIMIT MAX

CB MAX

DSON MIN

()

Most MOSFET data sheets have an RDSON specification

with typical and maximum values but no minimum value.

Assuming a normal distribution with typical as mean, the

minimum value can be estimated as

DSON MIN

DSON NOM

DSON MAX

()

(

)

(

)

()

=•

−

The LTC4213 gives higher gate drive than the manufac-

turer specified gate drive for RDSON. This gives a slightly

lower RDSON than specified. Operating temperature also

modulates the RDSON value.

Example Current Limit Calculation

An Si4410DY is used for current detection in a 5V supply

system with the LTC4213 VCB at 25mV (ISEL pin grounded).

The RDSON distribution for the Si4410DY is

Typical RDSON = 0.015Ω = 100%

Maximum RDSON = 0.02Ω = 133.3%

Estimated MIN RDSON = 2 • 15 – 20 = 0.010Ω = 66.7%

The RDSON variation due to gate drive is

RDSON @ 4.5VGS = 0.015Ω = 100% (spec. TYP)

RDSON @ 4.8VGS = 0.014Ω = 93% (MIN ∆VGSMAX)

RDSON @ 7VGS = 0.0123Ω = 82% (NOM ∆VGSMAX)

RDSON @ 8VGS = 0.012Ω = 80% (MAX ∆VGSMAX)

LTC4213IDDB Datasheet(PDF) 12 Page - Linear Technology

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