Datasheet

MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
16 ______________________________________________________________________________________
configured in automatic retry mode (see MOSFET
Thermal Considerations).
Using the MAX4271/MAX4273 in latched mode allows
the consideration of MOSFETs with higher R
DS(ON)
and
lower power ratings. A MOSFET can typically withstand
single-shot pulses with higher dissipation than the
specified package rating. Low MOSFET gate capaci-
tance is not necessary since the inrush current limiting
is achieved by limiting the gate dv/dt. Table 3 lists
some recommended manufacturers and components.
Sense Resistor
The slow comparator threshold voltage is set at 50mV.
Select a sense resistor that causes a 50mV voltage
drop at a current level above the maximum normal
operating current; typically, set the overload current at
1.2 to 1.5 times the nominal load current. The fast com-
parator threshold is typically set at 200mV. This will set
the fault current limit at four times the overload current
limit. The MAX4273 fast comparator threshold can be
set between 50mV and 750mV; see Table 4 for a
detailed listing.
Choose the sense resistor power rating according to
the device configuration. If no retry mode is selected,
P
RSENSE
= (I
OVERLOAD
)
2
x R
SENSE
; if retry is selected,
then P
RSENSE
= (I
FAULT
)
2
x R
SENSE
x (t
ON
/t
RETRY
).
Fast Comparator Threshold (RTH) (MAX4273)
The fast comparator threshold is determined by the
external resistor connected at RTH. To select threshold
voltages between 50mV and 750mV, use resistor val-
ues between 5kΩ and 75kΩ according to Figure 7.
Resistor values between 200Ω and 5kΩ are not recom-
mended. Setting the threshold voltage of the fast com-
parator below 50mV will effectively override the slow
comparator operation. The MAX4273 fast comparator
can be disabled by shorting the RTH pin to V
IN
(V
IN
-
25mV or less). Ground RTH to set the threshold to
200mV internally.
Startup and Retry Timers (CTIM, CTON)
The startup (t
START
) and retry (t
RETRY
) timers are deter-
mined by the capacitors connected at CTIM and
CTON. The capacitor connected to CTIM has two func-
tions for the three devices as follows:
Table 4. Current Levels vs. R
SENSE
R
SENSE
(mΩ) PART NUMBER
OVERLOAD THRESHOLD
SET BY SLOW COMPARATOR (A)
FAULT CURRENT THRESHOLD
SET BY FAST COMPARATOR (A)
MAX4271/MAX4272 5 20
10
MAX4273 5 5 to 75
MAX4271/MAX4272 1 4
50
MAX4273 1 1 to 15
MAX4271/MAX4272 0.5 2
100
MAX4273 0.5 0.5 to 7.5
Table 3. Component Manufacturers
COMPONENT MANUFACTURER PHONE WEB
Dale-Vishay 402-564-3131 www.vishay.com
Sense Resistors
IRC 704-264-8861 www.irctt.com
Fairchild 888-522-5372 www.fairchildsemi.com
International Rectifier 310-322-3331 www.irf.com
MOSFETS
Motorola 602-244-3576 www.mot-sps.com/ppd/
DEVICE CTIM FUNCTION
MAX4271 Startup time
MAX4272 Startup time and sets retry timer
MAX4273 Sets retry timer