MAX5920AESA Maxim Integrated Products, MAX5920AESA Datasheet - Page 15

• Manufacturer Part Number: MAX5920AESA
• Description: Hot Swap & Power Distribution
• Manufacturer: Maxim Integrated Products

Specifications of MAX5920AESA

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The circuit-breaker current-limit threshold is set to 50mV
(typically). Select a sense resistor that causes a drop
equal to or above the current-limit threshold at a current
level above the maximum normal operating current.
Typically, set the overload current to 1.5 to 2.0 times the
nominal load current plus the load-capacitance charging
current during startup. Choose the sense resistor power
rating to be greater than (V
•
•
•
•
•
•
•
•
• Set R2 = 10Ω.
• If an optocoupler is utilized as in Figure 14, deter-
mine the LED series resistor:
Determine load capacitance:
Determine load current, I
Select circuit-breaker current, for example:
Calculate R
Realize that I
tolerance.
Set allowable inrush current:
Determine value of C2:
Calculate value of C1:
Determine value of R3:
C
L
C
1
= C2 + C3 + module input capacitance
I
=
INRUSH
I
(
Component Selection Procedure
INRUSH
C
R
SENSE
R
2
Applications Information
7
3
+
CB
______________________________________________________________________________________
≤
=
C
C
I
≤
CB
R
2
150
gd
:
varies ±20% due to trip-voltage
3
+
V
0 8
SENSE
C
=
mA
)
.
IN NOMINAL
= 2 x I
I
2
µ
LOAD
x
(
45
s
x
CL



I
≤
µ
INRUSH
R
V
(
LOAD
)
=
A x C
typically k
I
2
40
IN MAX
SENSE
LED
LOAD
50
/ R
≤
(
I
mV
CB
mV
0 8
SENSE
V
.
.
≤
)
GS TH
L
)
Sense Resistor
−
5
−
−
x I
(
mA
1
2
V
I
CB MIN
V
.
LOAD
)
Ω
GS TH
)
(
(
)
or



)
-48V Hot-Swap Controller
Although the suggested optocoupler is not specified for
operation below 5mA, its performance is adequate for
36V temporary low-line voltage where LED current
would then be ≈2.2mA to 3.7mA. If R7 is set as high as
51kΩ, optocoupler operation should be verified over
the expected temperature and input voltage range to
ensure suitable operation when LED current ≈0.9mA for
48V input and ≈0.7mA for 36V input.
If input transients are expected to momentarily raise the
input voltage to >100V, select an input transient-volt-
age-suppression diode (TVS) to limit maximum voltage
on the MAX5920 to less than 100V. A suitable device is
the Diodes Inc. SMAT70A telecom-specific TVS.
Select Q1 to meet supply voltage, load current, efficien-
cy, and Q1 package power-dissipation requirements:
The lowest practical R
and with values from 14mΩ to 540mΩ, are available at
100V breakdown.
Ensure that the temperature rise of Q1 junction is not
excessive at normal load current for the package select-
ed. Ensure that I
does not exceed allowable transient-safe operating-area
limitations. This is determined from the SOA and tran-
sient-thermal-resistance curves in the Q1 manufacturer’s
data sheet.
Example 1:
I
acceptable, or R
ature is acceptable. An IRL520NS 100V NMOS with
R
D
with R
DPAK, but may be more costly because of a larger die
size).
Using the IRL520NS, V
efficiency ≥ 98.6% at 80°C. P
temperature rise above case temperature would be 5°C
due to the package θ
Of course, using the SUD40N10-25 would yield an effi-
ciency greater than 99.8% to compensate for the
increased cost.
LOAD
DS(ON)
2
PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS
with External R
DS(ON)
= 2.5A, efficiency = 98%, then V
≤ 180mΩ and I
DPAK, D
≤ 25mΩ and I
DS(ON)
CB
I
D(ON)
BV
current during voltage transients
JC
DS(ON)
2
PAK, or TO-220AB
DSS
DS
≤ 384mΩ at operating temper-
= 3.1°C/W thermal resistance.
≥ 3 x I
D(ON)
≤ 0.625V even at +80°C so
≥ 100V
D(ON)
, within budget constraints
D
LOAD
= 10A is available in
≤ 1.56W and junction
= 40A is available in
SENSE
DS
= 0.96V is
15