Datasheet

Unlike other circuit breaker ICs, the MAX4271/
MAX4272/MAX4273 regulate the current to a preset
level instead of completely turning off the external
N-FET if an overcurrent condition occurs during startup.
In startup mode, the gate drive current is limited to
100µA and decreases with the increase of the gate
voltage (see Gate Charge Current vs. Gate Voltage in
the Typical Operating Characteristics). This allows the
controller to slowly enhance the MOSFET. If the fast
comparator detects an overcurrent, the gate voltage is
momentarily discharged with a fixed 70µA current until
the load current through the sense resistor (R
SENSE
)
decreases below its threshold point. This effectively
regulates the inrush current during startup. Figure 3
shows the startup waveforms. STAT goes high at the
end of the startup period if no fault condition is present.
Normal Operation (DualSpeed/BiLevel)
In normal operation (after the startup timer has
expired), protection is provided by turning off the exter-
nal MOSFET when a fault condition is encountered.
DualSpeed/BiLevel fault protection incorporates two
comparators with different thresholds and response
times to monitor the current:
1)Slow comparator. This comparator has an externally
set response time (from 20µs to seconds) and a fixed
50mV threshold voltage. The slow comparator
ignores low-amplitude momentary current glitches.
After an extended overcurrent condition, a fault is
generated and the MOSFET gate is slowly dis-
charged.
2)Fast comparator. This comparator has a fixed 350ns
response time and a 200mV threshold voltage
(adjustable from 50mV to 750mV in MAX4273). The
fast comparator turns off the MOSFET immediately
after it detects a large amplitude event such as a
short circuit.
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 11
Figure 1. MAX4271/MAX4272 Functional Diagram
MAX4271
MAX4272
6
μ
A
SLOW COMPARATOR
FAST COMPARATOR
6
μ
A
2.45V
C
SPD
CSPD
INPUT
UVLO
LOGIC
CONTROL
DISCHARGE
ENABLE
V
IN
STAT
GND
CTIM
C
TIM
4
μ
A
0.1V
0.6V
ON
R
SENSE
N
M1
GATE
SENSE
IN
GATE
OVLO
ON COMPARATOR
GATE
DRIVE
V
SC,TH
50mV
V
SC,TH
200mV
150ms
DELAY
ON
V
IN
RISING
V
OUT
V
IN
CHARGE
PUMP
(1MHz)