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 8A (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 0.01A. 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.
MAX4772/MAX4773
200mA/500mA Selectable
Current-Limit Switches
_______________________________________________________________________________________
7
ON
FAULT
SWITCH ON/OFF
SUPPLY CURRENT MODE
Low
X
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
A (MAX)
VIH
200mA
500mA
Figure 3. MAX4772 Power-Up Sequence (VSEL and VIN Rise
Simultaneously)
VIN
VIN = 2V
VSEL
ISEL
500mA