MAX5924 MAXIM [Maxim Integrated Products], MAX5924 Datasheet - Page 13

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

Determining a circuit’s inrush current is necessary to
choose a proper MOSFET. The MAX5924/MAX5925/
MAX5926 regulate the inrush current by controlling the
output-voltage slew rate, but inrush current is also a
function of load capacitance. Determine an anticipated
inrush current using the following equation:
where C
the selected MAX5924/MAX5925/MAX5926 output slew
rate in V/ms. For example, assuming a load capaci-
tance of 100µF and using the value of SR = 10V/ms, the
anticipated inrush current is 1A. If a 16V/ms output slew
rate is used, the inrush current increases to 1.6A.
Choose SR so the maximum anticipated inrush current
does not trip the fast circuit-breaker comparator during
startup.
The MAX5924/MAX5925/MAX5926 limit the slew rate of
V
SLEW and GND to adjust the slew-rate limit. Floating
SLEW sets the maximum slew rate to the default value.
Calculate C
where SR is the desired slew rate in V/ms.
A 2µA (typ) pullup current clamped to 1.4V causes an
initial jump in the gate voltage, V
Figure 8b. PGOOD Behavior with Large Negative Input-Voltage
Step when V
OUT
I
INRUSH
. Connect an external capacitor, C
PGOOD
1V to 13.2V, n-Channel Hot-Swap Controllers
GATE
L
V
CC
is the load capacitance in Farads, and SR is
S
SLEW
( ) =
is Near V
A
C
using the following equation:
SLEW
______________________________________________________________________________________
C
Determining Inrush Current
S(MIN)
L
dV
= 330 10
200µs/div
dt
OUT
=
GATE
C
-9
L
/ SR
×
, if C
SR
SLEW
GATE
Slew Rate
× 1000
2V/div
1V/div
1V/div
, between
is small
Require No Sense Resistor
and the slew rate is slow (Figure 3). Figure 9 illustrates
how the addition of gate capacitance eliminates this ini-
tial jump. C
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
on voltage to a voltage greater than V
Figure 9. Impact of C
Figure 10. Adjustable Turn-On Voltage
V
S
R
R
2
1
( ) ARE FOR MAX5926 ONLY.
GATE
S
V
C
C
, and GND sets the programmable turn-
S
SLEW
L
= V
= 10µF
EN (EN1)
(EN2)
R
should not exceed 25nF.
GATE
CB
CC
MOSFET ONLY
= 1µF
CB
= 13.2V
on the V
EN (MAX5924/MAX5925),
MAX5924_
MAX5925_
MAX5926
10ms/div
GND
V
CC
GATE
EN1/ EN2 (MAX5926)
GATE
V
Waveform
S,TURN-ON
MOSFET AND
C
SC_DET
GATE
SENSE
OUT
UVLO
= 20nF
=
(R
2
+ R
(Figure 10).
1
5V/div
0V
0V
) V
R
2
EN/UVLO
R
SC
13