MAX4785 Просмотр технического описания (PDF) - Maxim Integrated

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MAX4785

50mA/100mA Current-Limit Switches

Maxim Integrated 

50mA/100mA Current-Limit Switches

REVERSE-CURRENT

DETECTOR

BLANKING TIME

CIRCUITRY

MAX4785/MAX4787

ONLY

FLAG

N

FORWARD CURRENT

DETECTOR

N

IN

OUT

ON

UNDERVOLTAGE

LOCKOUT

LOGIC

AUTO-

RETRY

+2.0V

GND

MAX4785–MAX4788

Figure 1. MAX4785–MAX4788 Functional Diagram

Detailed Description

The MAX4785–MAX4788 are forward/reverse current-

limited switches that operate from a 2.3V to 5.5V input

voltage range and guarantee a 50mA and 100mA mini-

mum current-limit threshold for different options. The

voltage drop across an internal sense resistor is com-

pared to two reference voltages to indicate a forward or

reverse current-limit fault. When the load current

exceeds the preset current limit for greater than the

fault-blanking time, the switch opens.

The MAX4786 and MAX4788 have an autoretry function

that turns on the switch again after an internal retry time

expires. If the faulty load condition is still present after

the blanking time, the switch turns off again and the

cycle is repeated. If the faulty load condition is not pre-

sent, the switch remains on.

The MAX4785 and MAX4787 do not have the autoretry

option and the switch remains in latch-off mode until

the ON pin or the input power is cycled from high to low

and then high again.

The undervoltage lockout (UVLO) circuit prevents erro-

neous switch operation when the input voltage goes too

low during startup conditions.

Reverse-Current Protection

The MAX4785–MAX4788 limit the reverse current (VOUT

to VIN) from exceeding the maximum IREV value. The

switch is shut off and FLAG is asserted (MAX4785/

MAX4787) if the reverse current-limit condition persists

for more than the blanking time. This feature prevents

excessive reverse currents from flowing through the

device.

Switch-On/Off Control

Toggle ON high to enable the current-limited switches.

The switches are continuously on, only if VIN exceeds

the UVLO threshold (typically 2V) and there is no fault.

When a forward/reverse current fault is preset or the die

exceeds the thermal-shutdown temperature of +150°C,

OUT is internally disconnected from IN and the supply

current decreases to 8µA (latch off). The switch is now

operating in one of its off states. The switch off-state

also occurs when driving ON low, thus reducing the

supply current (shutdown) to 0.01µA. Table 1 illustrates

the ON/OFF state of the MAX4785–MAX4788 current-

limit switches.

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