Rainbow-electronics MAX5943 Manual de usuario descargar pdf (Pagina 14)

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

14 ______________________________________________________________________________________

Undervoltage Lockout

The MAX5943 operates from 7.5V to 37V and has a

default 6.5V undervoltage lockout threshold. The external

MOSFETs remain off as long as V

> 6.5V and V

ON_REF

. The turn-on threshold is programmable by

connecting a resistor-divider at ON. When V

> 1.24V

and V

> 7.5V, GATE2 is enhanced to 5.5V, with respect

to OUT and the MAX5943 goes into normal operation.

Program the MAX5943’s turn-on voltage using the fol-

lowing formula:

where V

TURN_ON

is the desired turn-on voltage of the

MAX5943. Choose an R2 value in the 1kΩ range to

minimize error due to the ON bias current.

When operating the MAX5943, ON must remain above

its 1.24V threshold. If V

falls below its 1.24V thresh-

old, the power-supply MOSFETs (Q1 and Q2) turn off

immediately (less than 1µs). This allows the power sup-

ply to disconnect in the event of a fault condition

detected by the system, such as shorting of the output

to a different power-supply voltage or a FireWire signal

pin. If possible transient conditions exist at the main

power-supply line (IN), place an RC filter at ON to

reject transient voltage dips and to prevent unneces-

sary power-supply interruptions.

TURN ON

124

12= −













INA

INB

> V

INA

OUT

Figure 6. MAX5943 Power Switch Over ORing Timing Diagram

SENSE GATE1

OR_ADJGNDLATCHILIM

GATE2

PORT1

OUTIN

MAX5943

TIM

ONQ1

FAULT

SENSE GATE1

OR_ADJGNDLATCHILIM

GATE2

PORT2

OUTIN

MAX5943

TIM

ONQ1

FAULT

Figure 7. MAX5943 Operating in Reverse-Current Mode

(Routing Power from Port 1 to Port 2)

MAX5943

GND

Figure 8. Setting the MAX5943 Turn-On Voltage

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

ORing Switch Controller 1

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Rainbow-electronics MAX5943 Manual de usuario Pagina 14

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