Rainbow-electronics MAX5943 Manual do Utilizador descarregar pdf (Página 12)

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

12 ______________________________________________________________________________________

MAX5943B–MAX5943E Circuit Breaker

The MAX5943B–MAX5943E provide a circuit-breaker

function that protects against excessive load currents

and short-circuit conditions. The load current is monitored

by sensing the voltage across an external sense resistor

SENSE

) and disconnects the load from the power

source when the voltage across R

SENSE

, exceeds

the programmed circuit-breaker thresholds (V

) for

longer than the circuit-breaker timeout period, t

Unlike the MAX5943A, when an output short circuit or

overcurrent occurs, the MAX5943B–MAX5943E keep

GATE2 fully enhanced. The short-circuit current is limit-

ed only by the input source impedance, R

SENSE

, Q1’s

DS(ON),

Q2’s R

DS(ON)

, and any parasitic impedance in

the power path. If the excessive current condition per-

sists (as indicated by V

> V

) for longer than t

GATE2 turns off with a strong pulldown (I

G2 OFF

) to

quickly disconnect the power source from the load and

FAULT asserts low (Figure 3).

Exercise caution when using the MAX5943B–MAX5943E.

Unlike the MAX5943A, the MAX5943B–MAX5943E do not

limit the load current during t

. High current during t

may cause damage to external devices connected in the

power path.

Current-Limit/Circuit-Breaker Thresholds

The MAX5943 allows three selectable current-limit/cir-

cuit-breaker thresholds (V

). Choose the voltage

threshold by connecting ILIM to the appropriate level;

see Table 1.

Current-Limit/Circuit-Breaker

Timeout Period (t

ILIM

)

The MAX5943’s current-limit/circuit-breaker timeout

function disconnects power from the load if the current-

limit or circuit-breaker threshold voltage exceeds its

maximum limit for a programmable amount of time.

Connect TIM to IN for the MAX5943 default timeout

periods (see Table 2).

Adjust the fault timeout period (t

ILIM/

) by connect-

ing a resistor (R

TIM

) from TIM to GND (see the Typical

Operating Characteristics). Calculate the fault-limit

timeout period using the following equation:

where R

TIM

is in kΩ, t

ILIM

is in ms, and K = 1 for

MAX5943A, K = 32 for MAX5943B, K = 16 for

MAX5943C, K = 8 for MAX5943D, and K = 4 for the

MAX5943E.

tmstms

ILIM CB

TIM

() () .

()

==×025

Ω

OUT

LIMIT

OUT

GATE1

GATE2

FAULT

Figure 3. MAX5943B–MAX5943E Circuit-Breaker Timing Diagram

Table 1. Current-Limit/Circuit-Breaker

Trip Threshold Level

ILIM CONNECTION V

(mV)

Open 40

GND 50

IN 60

PART

DEFAULT

TIMEOUT,

TIM = IN

(ms)

PROGRAMMABLE

TIMEOUT RANGE

(4kΩ < R

TIM

< 50kΩ)

MAXIMUM

TIMEOUT,

TIM =

FLOATING

(ms)

MAX5943A 2 1.04ms to 11.05ms 12.5

MAX5943B 0.5 32.5µs to 345µs 4.8

MAX5943C 1 65µs to 690µs 9.6

MAX5943D 2 130µs to 1.38ms 19.2

MAX5943E 4 260µs to 2.76ms 38.4

Table 2. MAX5943_ Timeout Periods

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 18 19 20

ORing Switch Controller 1

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