MAX15090 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – 2.7V to 18V, 12A, Hot-Swap Solution with Current Report Output

MAX15090/MAX15090A
2.7V to 18V, 12A, Hot-Swap Solution
with Current Report Output
Charge Pump
An integrated charge pump provides the gate-drive volt-
age for the internal power MOSFET. The charge pump
generates the proper gate drive voltage above V_IN to
fully enhance the internal power MOSFET and guarantee
low R_ON operation during normal state conditions.
During startup, the internal charge pump drives the GATE
of the MOSFET with a fixed 5.7FA current to enhance the
internal MOSFET with 10V/ms slew rate (typ). Connect an
external capacitor (C_GATE) from GATE to GND to reduce
the output slew rate during startup. C_GATE can be
calculated according to the following formula:
C_GATE = (I_GATE x Dt)/DV_GATE
where I_GATE is 5.7FA (typ), Dt is the desired slew-rate
time, and DV_GATE is the voltage at the gate of the internal
MOSFET at turn-on.
The slew rate of the OUT pin during startup can be
controlled by I_GATE/C_GATE under light-load driving
conditions, or by the limited inrush current and the exter-
nal capacitive load, whichever is less.
(DV_OUT/Dt) = I_LIM/C_LOAD
Circuit-Breaker Comparator
and Current Limit
The current that passes through the internal power
MOSFET is com­pared to a circuit-breaker threshold. An
external resistor between CB and GND sets this thresh-
old according to the following formula:
I_CB = R_CB/3333.3
where I_CB is in amps and R_CB (the resistor between CB
and GND) is in ohms.
The circuit-breaker comparator is designed so the load
current can exceed the threshold for some amount of
time before tripping. The time delay varies inversely with
the overdrive above the threshold. The greater the over-
current condition, the faster the response time, allowi­ng
the devices to tolerate load transients and noise near the
circuit-breaker threshold. The maximum allowed external
resistor value is 40.2kω, which corresponds to a 12A
CB threshold setting. Programming the CB threshold to
a value higher than 12A could cause unsafe operating
conditions, resulting in damage to the devices.
The devices also feature catastrophic short-circuit
protec­tion. During normal operation, if OUT is shorted
directly to GND, a fast protection circuit forces the gate
of the internal MOSFET to discharge quickly and discon-
nect the output from the input.
Autoretry and Latch-Off Fault Management
During a fault condition, the devices turn off the intern­ al
MOSFET, disconnecting the output from the input. The
MAX15090A enters autoretry mode and restarts after
a t_RESTART time delay has elapsed. The MAX15090
latches off and remains off until the enable logic is cycled
off and on after a t_RESTART delay. The delay prevents
the latch-off device to restart and operate with an unsafe
power-dissipation duty cycle.
Fault-Status Output (FAULT)
FAULT is an open-drain output that asserts low when
a current-limit or an overtemperature-fault shutdown
occurs. FAULT remains low until the next startup cycle.
FAULT is capable of sinking up to 5mA current when
asserted.
Power-Good (PG) Delay
The devices feature an open-drain, power-good output
that asserts after a t_PG delay, indicating that the OUT
voltage has reached (0.9 x V_IN) voltage and (V_GATE -
V_OUT) > 3V.
Internal Regulator Output (REG)
The devices include a linear regulator that outputs 3.3V
at REG. REG provides power to the internal circuit blocks
of the devices and must not be loaded externally (except
for a resistor > 50kω connected from REG to EN). REG
requires at least a 1FF capacitor to ground for proper
operation.
Current Report Output (ISENSE)
The ISENSE pin is the output of an accurate current-
sense amplifier and provides a source current that is pro-
portional to the load current flowing into the main switch.
The factory-trimmed current ratio is set to 220FA/A. This
produces a scaled voltage by connecting a resistor
between I_{SENSE and} ground. This voltage signal then
goes to an ADC and provides digitized information of the
current supplied to the powered system.
Maxim Integrated
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