max5956 Maxim Integrated Products, Inc., max5956 Datasheet - Page 11

• Manufacturer Part Number: max5956
• Description: Low-voltage, Dual Hot-swap Controllers With Independent On/off Control
• Manufacturer: Maxim Integrated Products, Inc.

The startup period (t
50ms. The adjustable startup period feature allows sys-
tems to be customized for MOSFET gate capacitance
and board capacitance (C
adjusted with the resistance connected from TIM to GND
(R
startup 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
determined by the longer of the two timings, case A and
case B. Set the startup timer t
to 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:
• If the board capacitance (C
• If the gate capacitance is high, the MOSFETs turn
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:
Table 3. Component Manufacturers
Sense Resistors
MOSFETs
TIM
inrush current is low.
on slowly.
). R
Low-Voltage, Dual Hot-Swap Controllers with
Case A: Slow Turn-On (Without Current Limit)
START
COMPONENT
TIM
t
is the desired startup period.
must be between 4kΩ and 500kΩ. The
=
C
GATE
R
______________________________________________________________________________________
TIM
TIM
START
Setting the Startup Period, R
with the following equation:
× ∆
=
128 800
) is adjustable from 0.45ms to
BOARD
I
V
GATE
GATE
t
START
START
×
Dale-Vishay
IRC
Fairchild
International Rectifier
Motorola
). The startup period is
Startup Sequence
BOARD
+
pF
to be longer than t
Q
MANUFACTURER
GATE
) is small, the
ON
Independent On/Off Control
TIM
) is
ON
where:
C
(Figure 4).
∆V
Q
I
In this case, the inrush current depends on the MOSFET
gate-to-drain capacitance (C
capacitance from GATE to GND (C
load current (I
Example: Charging and Discharging Times Using
the Fairchild FDB7030L MOSFET
If V
V
data sheet specifies that the FDB7030L has approxi-
mately 60nC of gate charge and C
MAX5955/MAX5956 have a 100µA gate-charging cur-
rent and a 3mA strong discharging current.
Figure 4. Operating with an External Gate Capacitor
GATE
DRIVE
GATE
GATE
GATE
IN1
R
V
*
PULLUP
I
402-564-3131
704-264-8861
888-522-5372
310-233-3331
602-244-3576
is the gate-charging/discharging current.
INRUSH
IN
); therefore ∆V
= 5V then GATE1 charges up to 10.4V (V
is the MOSFET total gate charge.
is the external gate to ground capacitance
is the change in gate voltage.
PHONE
* REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION.
LOAD
=
PGOOD_
ON_
C
rss
IN_
) present during the startup period.
C
BOARD
+
GATE
R
C
SENSE
0.1µF
GATE
MAX5955
MAX5956
= 10.4V. The manufacturer’s
GND
www.vishay.com
www.irctt.com
www.fairchildsemi.com
www.irf.com
www.mot-sps.com/ppd
SENSE
rss
×
) plus any additional
I
GATE
GATE
WEBSITE
GATE
rss
+
= 600pF. The
), and on any
I
LOAD
V
OUT
C
C
GATE
BOARD
IN1
11
+