MAX5924 MAXIM [Maxim Integrated Products], MAX5924 Datasheet - Page 14

• Manufacturer Part Number: MAX5924
• Description: 1V to 13.2V, n-Channel Hot-Swap Controllers Require No Sense Resistor
• Manufacturer: MAXIM [Maxim Integrated Products]

1V to 13.2V, n-Channel Hot-Swap Controllers
Require No Sense Resistor
Figure 11. Maximum Circuit-Breaker Programming Resistor vs. Temperature
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
or R
After V
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
can be set between 10mV and 500mV. The value of the
circuit-breaker voltage must be carefully selected
based on V
When operating without R
breaker threshold using the MOSFET’s R
worst possible operating condition, and add a 20%
overcurrent margin to the maximum circuit current. For
example, if a MOSFET has an R
+25°C, and a normalized on-resistance factor of 1.75 at
T
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-
breaker threshold is then a product of these two num-
bers, 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.
14
A
= +105°C, the R
SENSE
______________________________________________________________________________________
Selecting a Circuit-Breaker Threshold
GS
exceeds V
S
15,000
12,000
(Figure 13), a voltage drop is generated.
9000
6000
3000
(Figure 11).
0
-40
TC = 0ppm/°C
V
V
V
V
V
V
S
S
S
S
S
S
= 1.5V
= 1.4V
= 1.3V
= 1.2V
= 1.1V
= 1.0V
DS(ON)
-15
CB,EN
TEMPERATURE (°C)
SENSE
10
, the MAX5924/MAX5925/
used for calculation is the
DS(ON)
, calculate the circuit-
35
DS(ON)
No R
60
of 0.06Ω at T
DS(ON)
SENSE
(Figure 12)
85
Mode
at the
A
CB
=
To determine the proper circuit-breaker resistor value
use the following equation, which refers to Figure 12:
where I
current.
Figure 12. Circuit Breaker Using R
R
V
S
CB
MAX5925
MAX5926
TRIPSLOW
SELECT
TC
=
15,000
12,000
9000
6000
3000
R
(
I
CB
TRIPSLOW
0
-40
TC = 3300ppm/°C
V
V
V
V
V
V
CB
is the desired slow-comparator trip
S
S
S
S
S
S
R
= 1.5V
= 1.4V
= 1.3V
= 1.2V
= 1.1V
= 1.0V
CBF
I
CB
R
-15
I
LOAD
DS(ON)
GATE
TEMPERATURE (°C)
x R
10
DS ON T
I
DS(ON)
SENSE
V
CB
V
CBF,TH
CB,TH
(
35
) ( )
OUT
V
V
CB,OS
CB,OS
)
60
+
V
SLOW
COMPARATOR
FAST
COMPARATOR
V
OUT
CB OS
85
,