allowing the voltage on the load, i.e. the drain of the
MOSFET, to fall no faster than 10V/ms (typ). The inrush
current to the load is thus limited to a level proportional
to the load capacitance, and the constant load voltage
slew rate. After the MOSFET is fully enhanced, and the
load voltage is settled to its final value, the MAX5900A/
MAX5901A and MAX5900L/MAX5901L monitor the volt-
age drop from the MOSFET’s drain-to-source (V
DS
). If
the voltage drop exceeds 75% of the circuit-breaker
threshold the MAX5900A/MAX5901A or MAX5900L/
MAX5901L turn off the MOSFET, disconnecting the
load immediately. Because the circuit-breaker function
is not activated until the MOSFET is fully enhanced, it
takes approximately 10ms for the MAX5900A/
MAX5901A or MAX5900L/MAX5901L to react to an out-
put short circuit at startup. If no circuit-breaker fault
exists, the power-good output is asserted. Then, if any
of four conditions exist, the power-good output
deasserts and the MOSFET is turned off . The four con-
ditions are: the voltage across the MOSFET exceeds
the circuit-breaker threshold; the supply voltage magni-
tude falls below the undervoltage lockout level; the die
temperature exceeds +125°C; or ON/OFF is forced low.
After a circuit-breaker fault, the MAX5900L/MAX5901L
keep the MOSFET off until the power is cycled, or the
part is reset by toggling ON/OFF low for at least 20ms
(typ). After a circuit-breaker fault, the MAX5900A/
MAX5901A automatically restart in 300ms (typ). All ver-
sions automatically restart after a thermal fault, or an
undervoltage shutdown, if the fault condition goes away
for at least 300ms (typ).
ON/OFF offers external control of the MAX5900/
MAX5901, facilitating power-supply sequencing, and
may also be used to change the UVLO level. UVLO
keeps the external MOSFET switched off as long as the
magnitude of the input voltage is less than a desired
level.
A power-good output, PGOOD (MAX5900) or PGOOD
(MAX5901), asserts when the external MOSFET is fully
enhanced and the drain-source voltage is at least 25%
below the circuit-breaker threshold. PGOOD and
PGOOD are open-drain outputs referenced to V
EE
, and
can withstand up to 100V above V
EE
.
A thermal shutdown feature protects the external MOS-
FET by turning it off if the die temperature of the
MAX5900/MAX5901 exceeds +125°C. The MAX5900/
MAX5901 must be in good thermal contact with the
external MOSFET. See the Layout Guidelines section in
the Applications Information.
A circuit-breaker function monitors the voltage across
the external MOSFET, V
DS
, and turns off the MOSFET if
V
DS
exceeds the circuit-breaker threshold, V
CB
. The
circuit-breaker function is enabled after the MOSFET is
fully enhanced. Three threshold voltage options are
available—200mV, 300mV, and 400mV. One version is
available with no circuit-breaker function. circuit-break-
er fault management for the MAX5900/MAX5901 is
offered with two different configurations—latched and
automatic retry.
Latched Circuit Breaker
After a circuit-breaker trip event, the latched versions
(MAX5900L/MAX5901L) drive GATE to V
EE
, turning off
the external MOSFET, and PGOOD (PGOOD) is
deasserted. A latched-off condition needs to be reset
by toggling ON/OFF low for at least 20ms, or by cycling
the power supply, V
EE
.
Automatic Retry Circuit Breaker
After a circuit-breaker trip event, the automatic retry
versions (MAX5900A/MAX5901A) drive GATE to V
EE
,
turning off the external MOSFET, and PGOOD
(PGOOD) is deasserted. If the start conditions are met
for a full 300ms (t
RS
) the start sequence is initiated. The
start conditions are: the device is not in UVLO; ON/OFF
is not driven low; and the device is not in thermal shut-
down.
No Circuit Breaker
For the versions without a circuit-breaker MAX5900N
(MAX5901N), PGOOD (PGOOD) is asserted when the
MOSFET is fully enhanced. Once powered up, the
MAX5900N/MAX5901N ignore the MOSFET drain-to-
source voltage (V
DS
) for applications where a circuit-
breaker function is not desired.
Applications Information
ON/
OFF
Control Input
The ON/OFF control input provides three hot-swap
functions: external ON/OFF control; setting of the UVLO
level; and resetting after a circuit-breaker event has
caused the MAX5900L/MAX5901L to turn off the exter-
nal MOSFET. Pulling ON/OFF to V
EE
for at least 20ms
(t
OFF
) forces the MAX5900/MAX5901 to turn off the
external MOSFET (see Figure 2 for a circuit example).
To reset the MAX5900L/MAX5901L after a circuit-
breaker event, toggle ON/OFF to V
EE
for at least 20ms
(t
OFF
).
ON/OFF can be used to sequence power supplies.
Connecting a capacitor from ON/OFF to V
EE
will delay
the rise of ON/OFF proportional to the capacitance and
input impedance of ON/OFF, typically 32kΩ (Figure 3).
MAX5900/MAX5901
-100V, SOT23/TDFN, Simple Swapper
Hot-Swap Controllers
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