MAX4772 datasheet(7/10 Pages) MAXIM

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Reverse-Current Protection

The MAX4772/MAX4773 limit the reverse current (VOUT to

VIN) from exceeding the maximum IREV value. The switch

is shut off and FLAG is asserted 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.

When a forward/reverse current fault is present 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 MAX4772/MAX4773 current-limit

switches.

FLAG Indicator

The MAX4772/MAX4773 feature a fault output (FLAG).

Whenever an overcurrent condition is encountered, the

MAX4772 latches FLAG low and turns the switch off.

The MAX4773 latches FLAG low and keeps it low until

the overcurrent conditon is removed. During this time,

the switch cycles on and off in the autoretry mode.

When the overcurrent condition is removed, FLAG

deasserts and the switch turns on (Figure 4).

FLAG is an open-drain output transistor and requires an

external pullup resistor from FLAG to IN. During shut-

down (ON is low), the pulldown on FLAG output is

released in order to limit power dissipation. FLAG goes

low when any of the following conditions occur:

• The die temperature exceeds the thermal-shutdown

temperature limit of +150°C.

• The device is in current limit for more than the fault-

blanking period.

• The switch is in autoretry.

Autoretry (MAX4773)

When the forward or reverse current-limit threshold is

exceeded, tBLANK timer begins counting (Figure 4).

The timer resets if the overcurrent condition disappears

before tBLANK has elapsed. A retry time delay (tRETRY)

is started immediately after tBLANK has elapsed and

during that time, the switch is latched off and FLAG

asserts. At the end of tRETRY, the switch is turned on

again. If the fault still exists, the cycle is repeated. If the

fault has been removed, the switch stays on and FLAG

deasserts.

200mA/500mA Selectable

Current-Limit Switches

_______________________________________________________________________________________

FAULT

SWITCH ON/OFF

SUPPLY CURRENT MODE

Low

OFF

Shutdown

High

Thermal

OFF immediately (tBLANK period does not apply)

Latch off

OFF after tBLANK period has elapsed

Latch off

High

Current Limit

ON during tBLANK period, OFF during tRETRY period for the

MAX4773 cycle repeats until fault is removed

See the Autoretry section

Table 1. MAX4772/MAX4773 Switch Truth Table

Figure 2. MAX4772/MAX4773 Power-Up Sequence (VSEL Rises

after Power-Up)

VIN

VIN ≥ 2V

VSEL

ISEL

100

µA (MAX)

VIH

200mA

500mA

Figure 3. MAX4772 Power-Up Sequence (VSEL and VIN Rise

Simultaneously)

VIN

VIN = 2V

VSEL

ISEL

500mA

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