Datasheet

MAX5924/MAX5925/MAX5926
1V to 13.2V, n-Channel Hot-Swap Controllers
Require No Sense Resistor
______________________________________________________________________________________ 15
EN (MAX5924/MAX5925),
EN1/
EN2 (MAX5926)
The enable comparators control the on/off function of
the MAX5924/MAX5925/MAX5926. Enable is also used
to reset the fault latch in latch mode. Pull EN or EN1 low
for 100µs to reset the latch. A resistive divider between
EN or EN1, V
S
, and GND sets the programmable turn-
on voltage to a voltage greater than V
UVLO
(Figure 10).
Selecting a Circuit-Breaker Threshold
The MAX5924/MAX5925/MAX5926 offer a circuit-break-
er function to protect the external MOSFET and the load
from the potentially damaging effects of excessive cur-
rent. As load current flows through R
DS(ON)
(Figure 12)
or R
SENSE
(Figure 13), a voltage drop is generated.
After V
GS
exceeds V
CB,EN
, the MAX5924/MAX5925/
MAX5926 monitor this voltage to detect overcurrent
conditions. If this voltage exceeds the circuit-breaker
threshold, the external MOSFET turns off and the
power-good output(s) deassert(s). To accommodate
different MOSFETs, sense resistors, and load currents,
the MAX5924/MAX5925/MAX5926 voltage across R
CB
can be set between 10mV and 500mV. The value of the
circuit-breaker voltage must be carefully selected
based on V
S
(Figure 11).
No R
SENSE
Mode
When operating without R
SENSE
, calculate the circuit-
breaker threshold using the MOSFET’s R
DS(ON)
at the
worst possible operating condition, and add a 20% over-
current margin to the maximum circuit current. For exam-
ple, if a MOSFET has an R
DS(ON)
of 0.06Ω at T
A
=
+25°C, and a normalized on-resistance factor of 1.75 at
T
A
= +105°C, the R
DS(ON)
used for calculation is the
product of these two numbers, or (0.06Ω) x (1.75) =
0.105Ω. Then, if the maximum current is expected to be
2A, using a 20% margin, the current for calculation is
(2A) x (1.2) = 2.4A. The resulting minimum circuit-break-
er threshold is then a product of these two numbers, or
(0.105Ω) x (2.4A) = 0.252V. Using this method to choose
a circuit-breaker threshold allows the circuit to operate
under worst-case conditions without causing a circuit-
breaker fault, but the circuit-breaker function will still
detect a short circuit or a gross overcurrent condition.
Figure 11. Maximum Circuit-Breaker Programming Resistor vs. Temperature
TEMPERATURE (°C)
R
CB(MAX)
(Ω)
603510-15
3000
6000
9000
12,000
15,000
0
-40 85
V
S
= 1.5V
V
S
= 1.4V
V
S
= 1.3V
V
S
= 1.2V
V
S
= 1.1V
V
S
= 1.0V
TC = 0ppm/°C
TEMPERATURE (°C)
R
CB(MAX)
(Ω)
603510-15
3000
6000
9000
12,000
15,000
0
-40 85
V
S
= 1.5V
V
S
= 1.4V
V
S
= 1.3V
V
S
= 1.2V
V
S
= 1.1V
V
S
= 1.0V
TC = 3300ppm/°C
EN (EN1)
CB
SENSE
GATE
V
S
MAX5924_
MAX5925_
MAX5926
R
1
R
2
(R
2
+ R
1
) V
EN/UVLO
R
2
( ) ARE FOR MAX5926 ONLY.
OUT
SC_DET
(EN2)
V
CC
GND
R
CB
V
S,TURN-ON
=
R
SC
Figure 10. Adjustable Turn-On Voltage