MAX5927A Datasheet, PDF (18/23 Pages) Maxim Integrated Products – Low-Voltage, Quad, Hot-Swap Controllers/Power Sequencers

Low-Voltage, Quad, Hot-Swap
Controllers/Power Sequencers
Table 6. Recommended n-Channel MOSFETs
PART NUMBER
IRF7413
IRF7401
IRL3502S
MMSF3300
MMSF5N02H
MTB60N05H
FDS6670A
ND8426A
FDB8030L
MANUFACTURER
International Rectifier
On Semiconductor
Fairchild Semiconductor
DESCRIPTION
11mΩ, 8-pin SO, 30V
22mΩ, 8-pin SO, 20V
6mΩ, D²PAK, 20V
20mΩ, 8-pin SO, 30V
30mΩ, 8-pin SO, 20V
14mΩ, D²PAK, 50V
10mΩ, 8-pin SO, 30V
13.5mΩ, 8-pin SO, 20V
4.5mΩ, D²PAK, 30V
Table 7. Component Manufacturers
COMPONENT
Sense Resistors
MOSFETs
MANUFACTURER
Vishay/Dale Resistors
IRC, Inc.
International Rectifier
Fairchild Semiconductor
On Semiconductor
PHONE
402-564-3131
361-992-7900
310-322-3331
888-522-5372
602-244-6600
WEBSITE
www.vishay.com
www.irctt.com
www.irf.com
www.fairchildsemi.com
www.onsemi.com
Sense Resistor
The slow-comparator threshold voltage is adjustable
from 25mV to 100mV. Select a sense resistor that caus-
es a drop equal to the slow-comparator threshold volt-
age at a current level above the maximum normal
operating current. Typically, set the overload current at
1.2 to 1.5 times the full load current. The fast-compara-
tor threshold is two times the slow-comparator thresh-
old in normal operating mode. Choose the sense
resistor power rating to be greater than or equal to 2 x
(I_OVERLOAD) x V_SC,TH. Table 7 lists some recommend-
ed sense resistor manufacturers.
Slow-Comparator Threshold, R_{LIM_} (MAX5927A)
The slow-comparator threshold voltage is adjustable
from 25mV to 100mV, allowing designers to fine-tune the
current-limit threshold for use with standard-value sense
resistors. Low slow-comparator thresholds allow for
increased efficiency by reducing the power dissipated
by the sense resistor. Furthermore, the low 25mV slow-
comparator threshold is beneficial when operating with
supply rails down to 1V because it allows a small per-
centage of the overall output voltage to be used for cur-
rent sensing. The VariableSpeed/BiLevel fault protection
feature offers inherent system immunity against load
transients and noise. This allows the slow-comparator
threshold to be set close to the maximum normal
operating level without experiencing nuisance faults. To
adjust the slow-comparator threshold, calculate R_{LIM_}
as follows:
R_{LIM_} =
V_TH − 25mV
7.5μA
where V_TH is the desired slow-comparator threshold
voltage. Shorting LIM_ to GND sets V_TH to 25mV. Do
not leave LIM_ unconnected.
Setting the Startup Period, R_TIM
The startup period (t_START) is adjustable from 0.4ms to
50ms. The adjustable startup period feature allows sys-
tems to be customized for MOSFET gate capacitance
and board capacitance (C_BOARD). The startup period
is adjusted with a resistor connected from TIM to GND
(R_TIM). R_TIM must be between 4kΩ and 500kΩ. The
startup period has a default value of 9ms when TIM is
left unconnected. Calculate R_TIM with the following
equation:
R_TIM
=
t_START
128 × 800pF
where t_START is the desired startup period.
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