max5905 Maxim Integrated Products, Inc., max5905 Datasheet - Page 17

• Manufacturer Part Number: max5905
• Description: Low-voltage, Dual Hot-swap Controllers/power Sequencers
• Manufacturer: Maxim Integrated Products, Inc.

Table 2. Recommended n-Channel
MOSFETs
slow-comparator threshold is beneficial when operating
with supply rails down to 1V because it allows a small
percentage of the overall output voltage to be used for
current sensing. The VariableSpeed/BiLevel fault pro-
tection feature offers inherent system immunity against
load transients and noise. This allows the slow-com-
parator threshold to be set close to the maximum nor-
mal operating level without experiencing nuisance
faults. Typically, set the overload current at 1.2 to 1.5
times the nominal load current. To adjust the slow-com-
parator threshold calculate R
where V
voltage.
The startup period (t
fixed at 9ms, and adjustable from 0.4ms to 50ms for the
MAX5906–MAX5909. The adjustable startup period of
the MAX5906–MAX5909 systems can be customized for
MOSFET gate capacitance and board capacitance
(C
tance connected from TIM to GND (R
Table 3. Component Manufacturers
Sense Resistors
MOSFETs
PART NUMBER
IRF7413
IRF7401
IRL3502S
MMSF3300
MMSF5N02H
MTB60N05H
FDS6670A
NDS8426A
FDB8030L
Low-Voltage, Dual Hot-Swap Controllers/Power
BOARD
COMPONENT
TH
). The startup period is adjusted with the resis-
is the desired slow-comparator threshold
R
LIM
MANUFACTURER
______________________________________________________________________________________
START
International
=
Setting the Startup Period, R
Motorola
Fairchild
Rectifier
V
TH
0 25
.
) of the MAX5904/MAX5905 is
−
25
LIM
µ
Dale-Vishay
IRC
International Rectifier
Fairchild
Motorola
A
mV
as follows:
MANUFACTURER
TIM
11mΩ, 8 SO, 30V
22mΩ, 8 SO, 20V
6mΩ, D2PAK, 20V
20mΩ, 8 SO, 30V
30mΩ, 8 SO, 20V
14mΩ, D2PAK, 50V
10mΩ, 8SO, 30V
13.5mΩ, 8 SO, 20V
4.5mΩ, D2PAK, 30V
DESCRIPTION
). R
TIM
must be
TIM
between 4kΩ and 500kΩ. The MAX5906–MAX5909 start-
up period has a default value of 9ms when TIM is left
floating. Calculate R
where t
There are two ways of completing the startup
sequence. Case A describes a startup sequence that
slowly turns on the MOSFETs by limiting the gate
charge. Case B uses the current-limiting feature and
turns on the MOSFETs as fast as possible while still
preventing a high inrush current. The output voltage
ramp-up time (t
two timings, case A and case B. Set the MAX5906–
MAX5909 startup timer t
guarantee enough time for the output voltage to settle.
There are two ways to turn on the MOSFETs without
reaching the fast-comparator current limit:
In both cases, the turn-on time is determined only by the
charge required to enhance the MOSFET. The small
gate-charging current of 100µA effectively limits the out-
put voltage dV/dt. Connecting an external capacitor
between GATE and GND extends turn-on time. The time
required to charge/discharge a MOSFET is as follows:
where:
C
(Figure 4)
∆V
GATE
GATE
If the board capacitance (C
inrush current is low.
If the gate capacitance is high, the MOSFETs turn
on slowly.
402-564-3131
704-264-8861
310-233-3331
888-522-5372
602-244-3576
Case A: Slow Turn-On (Without Current Limit)
START
is the external gate to ground capacitance
is the change in gate voltage
PHONE
t
=
is the desired startup period.
C
ON
R
GATE
TIM
) is determined by the longer of the
TIM
=
× ∆
with the following equation:
128 800
START
I
V
GATE
t
Sequencers
GATE
START
×
www.vishay.com
www.irctt.com
www.irf.com
www.fairchildsemi.com
www.mot-sps.com/ppd
to be longer than t
+
pF
BOARD
Q
GATE
WEBSITE
) is small, the
ON
17
to