max5938 Maxim Integrated Products, Inc., max5938 Datasheet - Page 23

• Manufacturer Part Number: max5938
• Description: Max5938 -48v Hot-swap Controller With Vin Step Immunity, No Rsense, And Overvoltage Protection
• Manufacturer: Maxim Integrated Products, Inc.

∆V
excursion required to trip the respective fault.
R
gives a ∆V
0.13V, and a worst-case high of 0.37V. In finding τ
in the equation below, use ∆V
ensure sufficient margin with worst-case I
To set τ
ramp rate, find the ratio of ∆V
choose τ
and since R
After the first-pass component selection, if sufficient
timing margin exists, it is possible (but not necessary)
to lower R
STEP_MON to V
It is prudent to verify conclusively that all circuit-breaker
and short-circuit faults will be blocked for all ramp
rates. To do this, some form of graphical analysis is
recommended but first, find the value of τ
load by a series of ramp tests as indicated earlier.
These tests include evaluating the load with a series of
V
rate of rise of V
should have a constant slope. The V
must be taken only during the positive ramp. Data
taken after V
must not be used.
Figure 21 shows the load in parallel with the load
capacitor, C
with the power MOSFET, which is fully enhanced with
V
the V
Figure 22 shows the general response of V
ramp over time t. Equation 1 gives the response of V
to a ramp of dV/dt. The product (dV/dt) x τ
∆V
the V
ter of interest is ∆V
necessary to subtract the DC shift in V
load resistance. For some loads, which are relatively
independent of supply voltage, this may be insignificant.
where I
be determined separately with DC tests.
-48V Hot-Swap Controller with V
IN
GS
STEP_MON
C
CB
OUT
ramps of increasing ramp rates and monitoring the
STEP_MON
= 10V. The objective is to determine τ
OUT
IN
and ∆V
(max) or the maximum V
LOAD
ramp were to continue indefinitely. The parame-
τ
STEP
STEP
STEP
V
response.
STEP
OUT
STEP_MON
STEP_MON
LOAD
will typically be set to 100kΩ ±1%. This
IN
SC
is a function of the V
to block all V
so:
= 1.2 x τ
= τ
(t) = V
below 100kΩ to reduce the sensitivity of
has leveled off at the new higher value
IN
OUT
and they represent the minimum V
, and the parallel connection in series
STEP
______________________________________________________________________________________
noise.
OUT
OUT
during the ramp. Each V
= 100kΩ:
C
/ R
of 0.25V, a worst-case low of
due to the ramp dV/dt, thus it is
No R
(t) – R
x ∆V
Verification of the Step
STEP_MON
CB
STEP_MON
OUT
DS(ON)
STEP_MON
and V
STEP_MON
OUT
voltage differential if
SENSE
Monitor Timing
OUT
= τ
SC
x I
level that should
STEP
OUT
/ ∆V
LOAD
STEP_OS
response data
faults for any
to ∆V
OUT
L,eqv
= 0.37V to
CB
due to the
/ 100kΩ
L,eqv
IN
to a V
CB
.
of the
, and Overvoltage Protection
ramp
STEP
from
OUT
OUT
C
and
IN
=
Figure 21. V
Figure 23. V
Figure 22. General Response of V
V
V
IN
IN
V
= GND = V
RAMP
OUT
i
EE
0
IN
OUT
2.7
2.4
2.1
1.8
1.5
1.2
0.9
0.6
0.3
0
V
Ramp Test Of Load
OUT
0
dv
A = V
B = ∆V
C = ∆V
dt
t1
Response to V
IN
V
V
t
CB
IN
IN
τ
C
RESPONSE TO V
RAMP
IN
1
t2
t
STEP_MON
OUT
STEP
(GND - V
Step Immunity,
2
LOAD CAPACITOR
WITH PARASITICS
dv
dt
t3
EE
R
t
3
)
t4
SC
DS,ON
10V
TIME (µs)
D
IN
4
IN
Ramp of 300V/ms
OUT
RAMP OF 300V/ms
E
5
D = ∆V
E = ∆V
F = ∆V
C
to a V
LOAD
F
d
R
VIN
dt
6
EQV
CB
SC
L
STEP,TH
EQU
C
IN
7
A
B
Ramp
8
V
V
IN
OUT
LOAD
.F
23