Datasheet

10 Maxim Integrated
Adjustable Overvoltage and Overcurrent
Protectors with High Accuracy
MAX14571/MAX14572/MAX14573
Detailed Description
The MAX14571/MAX14572/MAX14573 are adjust-
able overvoltage- and overcurrent-protection devices
designed to protect systems against positive and nega-
tive input voltage faults up to Q40V, and feature low
100mI (typ) on-resistance FETs. If the input voltage
exceeds the OVLO threshold or falls below the UVLO,
the internal FETs are turned off to prevent damage to the
protected components. If the OVLO or the UVLO pin is
set below the external OVLO or UVLO select thresholds
(V
OVLOSEL
and V
UVLOSEL
), the device automatically
selects the internal Q3% (typ) accurate trip thresholds.
The internal OVLO threshold is preset to 33V (typ), and
the internal UVLO threshold is preset to 19.2V (typ).
The ICs feature programmable current-limit protection
up to 4.2A. Once current reaches the threshold, the
MAX14571 turns off after 20.7ms (typ) blanking time and
stays off during the retry period. The MAX14572 latches
off after the blanking time, and the MAX14573 limits the
current continuously.
Programmable Current Limit/Threshold
A resistor from SETI to GND sets the current limit/thresh-
old for the switch (see the Setting the Current Limit/
Threshold section). If the output current is limited at the
current threshold value for a time equal to or longer than
t
BLANK
, the output FLAG asserts and the MAX14571
enters the autoretry mode, the MAX14572 latches off
the switch, and the MAX14573 enters the continuous
current-limit mode.
Autoretry (MAX14571)
When the current threshold is reached, the t
BLANK
timer
begins counting. The FLAG asserts if the overcurrent
condition is present for t
BLANK
. The timer resets if the
overcurrent condition disappears before t
BLANK
has
elapsed. A retry time delay, t
RETRY
, is started immediately
after t
BLANK
has elapsed and during t
RETRY
time, the
FETs are off. At the end of t
RETRY
, the FETs are turned
on again. If the fault still exists, the cycle is repeated and
the FLAG stays low. When the fault is removed, the FETs
stay on. If the die temperature exceeds +150NC (typ)
due to self-heating, the MAX14571 enables thermal shut-
down until the die temperature drops by approximately
30NC (Figure 1).
The autoretry feature reduces the system power in case
of overcurrent or short-circuit conditions. During t
BLANK
time, when the switch is on, the supply current is held
at the current limit. During t
RETRY
time, when the switch
is off, there is no current through the switch. Thus, the
output current is much less than the programmed cur-
rent limit. Calculate the average output current using the
following equation:
BLANK
LOAD LIM
BLANK RETRY
t
II
tt

=

+

With a 20.7ms (typ) t
BLANK
and 600ms (typ) t
RETRY
, the
duty cycle is 3.3%, resulting in a 96.7% power savings.
Latch-Off (MAX14572)
When the current threshold is reached, the t
BLANK
timer
begins counting. The FLAG asserts if the overcurrent
condition is present for t
BLANK
. The timer resets when
the overcurrent condition disappears before t
BLANK
has elapsed. The switch turns off and stays off if the
overcurrent condition continues beyond the blanking
time. To reset the switch, either toggle the control logic
EN or HVEN or cycle the input voltage. If the die tem-
perature exceeds +150NC (typ) due to self-heating, the
MAX14572 latches off (Figure 2.)
Continuous Current Limit (MAX14573)
When the current threshold is reached, the MAX14573
limits the output current to the programmed current limit.
The FLAG asserts if the overcurrent condition is present
for t
BLANK
and deasserts when the overload condition is
removed. If the die temperature exceeds +150NC (typ) due
to self-heating, the MAX14573 enables thermal shutdown
until the die temperature drops by approximately 30NC
(Figure 3).
Reverse-Current Enable (RIEN)
This feature disables the reverse-current protection
and enables reverse-current flow from OUT to IN. The
reverse-current enable feature is useful in applications
with inductive loads.
Fault Flag Output
FLAG is an open-drain fault indicator output and requires
an external pullup resistor to a DC supply. FLAG goes
low when any of the following conditions occur:
• The blanking time has elapsed.
• The reverse-current protection has tripped.
• The die temperature exceeds +150NC.
• SETI is connected to ground.
• OVLO threshold is reached.