Datasheet MAX4271, MAX4272, MAX4273 (Maxim) - 10

3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection Pin Description (continued) PIN MAX4271 FUNCTION MAX4273 NAME MAX4272
Startup and Retry Timers Input. Controls the startup time and the autoretry time (32x startup time) in the MAX4272, only the autoretry time in the MAX4273, and only the 6 11 CTIM startup time in the MAX4271. Leave floating or connect the timing capacitor from CTIM to GND. Connect to IN for latched mode (this prevents autoretry in MAX4273). See Startup and Retry Timers section. Status Output. High indicates startup completed with no fault (Table 1). STAT is an 7 12 STAT open-drain output. ON Comparator Input. Connect high for normal operation; connect low to force the MOSFET off. Comparator threshold VTH,ON = 0.6V allows for precise control over 8 13 ON shutdown feature. Pulse ON low for 20μs min to unlatch after a fault (MAX4273 in latched mode, or MAX4271). Negative pulses are ignored during autoretry (MAX4273 in autoretry mode, or MAX4272). See ON and Reset Comparators section. — 14 REF 1.2V Reference Output.
Do not bypass with a capacitor to GND.
— 15 INC Uncommitted Comparator Input. Controls OUTC. Uncommitted Comparator Output. OUTC goes high 150ms after INC goes high. OUTC — 16 OUTC goes low immediately after INC goes low. OUTC is an open-drain output.
Detailed Description
• Autoretry timeout period (time the part is shut down
MAX4271/MAX4272/MAX4273
after an overcurrent event) The MAX4271/MAX4272/MAX4273 are circuit breaker ICs designed for hot-swap applications where a line • Fault management (latched/autoretry) card is inserted into a live backplane. Normally, when a • Current overload threshold line card is plugged into a live backplane, the card’s discharged filter capacitors provide a low impedance
Startup Mode
that can momentarily cause the main power supply to CTIM (MAX4271/MAX4272) or CTON (MAX4273) sets collapse. The MAX4271/MAX4272/MAX4273 are the startup period (see Startup and Retry Timers). The designed to reside either in the backplane or in the startup period begins after three conditions are met: removable card to provide inrush current limiting and 1) 150ms after VIN exceeds the UVLO threshold (see short-circuit protection. This is achieved by using an Over/Undervoltage Lockouts) external N-channel MOSFET, an external current-sense
AND
resistor, and two on-chip comparators. Figures 1 and 2 show the functional diagrams. 2) 10µs after VON >0.6V The timing and voltage levels for several critical parame-
AND
ters can be adjusted with external resistors, external 3) The device is no longer in retry mode. capacitors, or by pin strapping. The timing components During startup, the slow comparator is disabled and the are optional; without them, the part is set to its nominal inrush current can be limited in two ways: values, as shown in the Electrical Characteristics. The parameters that can be adjusted are: 1) Slow ramping of the current to the load by control- ling the external MOSFET gate voltage • Current-limit threshold
OR
• Slow comparator response time 2) Limiting the current to the load by regulating the volt- • Startup timer age across the external current-sense resistor • Fast comparator threshold
10 ______________________________________________________________________________________