max5939eesat Maxim Integrated Products, Inc., max5939eesat Datasheet - Page 15

• Manufacturer Part Number: max5939eesat
• Description: -48v Hot-swap Controllers With External Rsense And High Gate Pulldown Current
• Manufacturer: Maxim Integrated Products, Inc.

Figure 14. MAX5921A Overcurrent Fault Example
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
ciency ≥ 98.6% at 80°C. P
ature rise above case temperature would be 5°C due to
the package θ
course, using the SUD40N10-25 will yield an efficiency
greater than 99.8% to compensate for the increased cost.
If I
bles to ≤ 1.25V. If C
voltage is ∆36V, the 5A charging-current pulse is:
LOAD
DS(ON)
2
CB
PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS
V
V
SENSE
GATE
V
OL
is set to twice I
DS(ON)
= 2.5A, efficiency = 98%, then V
≤ 180mΩ and I
t
1
t
2L
≤ 25mΩ and I
t
t
3H
4L
JC
DS(ON)
t
-48V Hot-Swap Controllers with External
CB
5H
______________________________________________________________________________________
R
= 3.1°C/W thermal resistance. Of
LOAD
OUT
current during voltage transients
SENSE
DS
DS(ON)
500µs x 128
≤ 384mΩ at operating temper-
D
≤ 0.625V even at +80°C so effi-
= 4000µF, transient-line input
, or 5A, V
D(ON)
≤ 1.56W and junction temper-
D(ON)
, within budget constraints
= 10A is available in
= 40A is available in
DS
and High Gate Pulldown Current
momentarily dou-
DS
= 0.96V is
Entering the data sheet transient-thermal-resistance
curves at 1ms provides a θ
so ∆t
Example 2:
I
but R
R
Power dissipation is 9.6W at +25°C or 14.4W at +80°C.
Junction-to-case thermal resistance is 1.9°C/W, so the
junction temperature rise would be approximately 5°C
above the +25°C case temperature. For higher efficien-
cy, consider IRL540NS with R
allows η = 99%, P
(θ
Thermal calculations for the transient condition yield
I
0.12°C/W, P
Good thermal contact between the MAX5921/MAX5939
and the external MOSFET is essential for the thermal-
shutdown feature to operate effectively. Place the
MAX5921/MAX5939 as close as possible to the drain of
the external MOSFET and use wide circuit-board traces
for good heat transfer. See Figure 15 for an example of
recommended layout for Kelvin-sensing current
through a sense resistor on a PC board.
Figure 15. Recommended Layout for Kelvin-Sensing Current
Through Sense Resistor
LOAD
CB
DS(ON)
JC
= 20A, V
= 1.1°C/W) at +25°C.
JC
DS(ON)
= 10A, efficiency = 98%, allowing V
= 5.6°C. Clearly, this is not a problem.
≤ 90mΩ at +25°C and ≤ 135mΩ at +80°C.
D
≤ 96mΩ. An IRF530 in a D
t
= 36W and ∆t
DS
=
MAX5921
MAX5939
= 1.8V, t = 0.5ms, transient θ
HIGH-CURRENT PATH
4000
SENSE V
D
µ
F x
5
≤ 4.4W, and T
EE
A
JC
JC
1 25
.
= 4.3°C.
= 0.9°C/W. P
Layout Guidelines
DS(ON)
V
=
SENSE RESISTOR
1
ms
≤ 44mΩ. This
2
PAK exhibits
JC
DS
D
= 6.25W,
= +4°C
= 0.96V
JC
15
=