LTC4210 Просмотр технического описания (PDF) - Linear Technology

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производитель

LTC4210

Hot Swap Controller in 6-Lead SOT-23 Package

Linear Technology 

LTC4210-1/LTC4210-2

APPLICATIO S I FOR ATIO

Current Limit Circuit Breaker Function

The LTC4210 features a current limiting circuit breaker

instead of a traditional comparator circuit breaker. When

there is a sudden load current surge, such as a low

impedance fault, the bus supply voltage can drop signifi-

cantly to a point where the power to an adjacent card is

affected, causing system malfunctions. The LTC4210 fast

response error amplifier (EA) instantly limits current by

reducing the external MOSFET GATE pin voltage. This

minimizes the bus supply voltage drop and permits power

budgeting and fault isolation without affecting neighbor-

ing cards. A compensation circuit should be connected to

the GATE pin for current limit loop stability.

Sense Resistor Consideration

The nominal fault current limit is determined by a sense

resistor connected between VCC and the SENSE pin as

given by Equation 1.

ILIMIT(NOM)

=

VCB(NOM)

RSENSE(NOM)

=

50mV

RSENSE(NOM)

(1)

The power rating of the sense resistor should be rated at

the fault current level. Table 2 in the Appendix lists some

common sense resistors.

For proper circuit breaker operation, Kelvin-sense PCB

connections between the sense resistor and the LTC4210

VCC and SENSE pins are strongly recommended. The

drawing in Figure 1 illustrates the connections between

the LTC4210 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.

CURRENT FLOW

TO LOAD

TRACK WIDTH W:

0.03" PER AMP

W

ON 1 OZ COPPER

CURRENT FLOW

SENSE RESISTOR

TO LOAD

TO TO

VCC SENSE

4210 F01

Figure 1. Making PCB Connections to the Sense Resistor

Calculating Current Limit

For a selected RSENSE, the nominal load current is given by

Equation 1. The minimum load current is given by

Equation 2:

ILIMIT(MIN)

=

VCB(MIN)

RSENSE(MAX)

=

44mV

RSENSE(MAX)

(2)

where

RSENSE(MAX)

=

RSENSE

•

1+

RTOL

100



The maximum load current is given by Equation 3:

ILIMIT(MAX)

=

VCB(MAX)

RSENSE(MIN)

=

56mV

RSENSE(MIN)

(3)

where

RSENSE(MIN)

=

RSENSE

•

1–

RTOL

100



421012f

9

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