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MAX15090A Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX15090A Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 15 page 11 Maxim Integrated 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 VIN to fully enhance the internal power MOSFET and guarantee low RON 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 (CGATE) from GATE to GND to reduce the output slew rate during startup. CGATE can be calculated according to the following formula: CGATE = (IGATE x Dt)/DVGATE where IGATE is 5.7FA (typ), Dt is the desired slew-rate time, and DVGATE 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 IGATE/CGATE under light-load driving conditions, or by the limited inrush current and the exter- nal capacitive load, whichever is less. (DVOUT/Dt) = ILIM/CLOAD 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: ICB = RCB/3333.3 where ICB is in amps and RCB (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 internal MOSFET, disconnecting the output from the input. The MAX15090A enters autoretry mode and restarts after a tRESTART time delay has elapsed. The MAX15090 latches off and remains off until the enable logic is cycled off and on after a tRESTART 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 tPG delay, indicating that the OUT voltage has reached (0.9 x VIN) voltage and (VGATE - VOUT) > 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 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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