MAX15091 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – Solution with Current Report Output

MAX15091/MAX15091A
2.7V to 18V, 9A, Integrated 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 5.7µA 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 ∆t)/∆V_GATE
where I_GATE is 5.7µA (typ), Dt is the desired slew-rate
time, and ∆V_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.
(∆V_OUT/∆t) = 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 threshold
according to the following formula:
I_CB = R_CB/2777.8
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 25kΩ, which corresponds to a 9A CB
threshold setting. Programming the CB threshold to a
value higher than 9A could cause unsafe operating condi-
tions, resulting in damage to the devices.
The devices also feature catastrophic short-circuit protec­
tion. 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 disconnect the
output from the input.
Autoretry and Latch-Off Fault Management
During a fault condition, the devices turn off the inter­nal
MOSFET, disconnecting the output from the input. The
MAX15091A enters autoretry mode and restarts after
a t_RESTART time delay has elapsed. The MAX15091
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 volt-
age 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 1µF 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 170µA/A.
This produces a scaled voltage by connecting a resistor
between ISENSE _and ground. This voltage signal then
goes to an ADC and provides digitized information of the
current supplied to the powered system.
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