LTC4216CMS View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4216CMS' PDF : 24 Pages View PDF
LTC4216
Applications Information
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.
CURRENT FLOW
TO LOAD
CURRENT FLOW
TO LOAD
TRACK WIDTH W:
0.03˝ PER AMPERE W
ON 1OZ COPPER
SENSE RESISTOR
where
RSENSE(MAX)
=
RSENSE(TYP)
• 1+
RTOL
100
The maximum load current that trips the circuit breaker
is given by:
ITRIP(MAX)
=
∆VCB(TH,MAX)
RSENSE(MIN)
=
28.5mV
RSENSE(MIN)
where
(15)
RSENSE(MIN)
=
RSENSE(TYP)
• 1–
RTOL
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.
4216 F12
TO
SENSEP
TO
SENSEN
Figure 12. Making PCB Connections to the Sense Resistor
Circuit Breaker Trip Current Calculation
For a selected RSENSE value, the typical load current that
trips the circuit breaker is given by:
ITRIP(TYP)
=
∆VCB(TH,TYP)
RSENSE(TYP)
=
25mV
RSENSE(TYP)
(13)
The minimum load current that trips the circuit breaker
is given by:
ITRIP(MIN)
=
∆VCB(TH,MIN)
RSENSE(MAX)
=
21.5mV
RSENSE(MAX)
(14)
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
data sheet 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:
4216fa
18
For more information www.linear.com/LTC4216
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