MAX5929BEEG+【PDF 18/23 页】IC HOT SWAP CTLR QUAD 24QSOP

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Sheet目录43

14页 15页 16页 17页 [18页]19页 20页 21页 22页

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

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:

where V

is the desired slow-comparator threshold

voltage. Shorting LIM_ to GND sets V

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

TIM

). R

TIM

must be between 4k?and 500k? The

startup period has a default value of 9ms when TIM is

left unconnected. Calculate R

TIM

with the following

equation:

where t

START

is the desired startup period.

TIM

START

?/DIV>

128 800

LIM

7 5

Low-Voltage, Quad, Hot-Swap

Controllers/Power Sequencers

18 _______________________________________________________________________ ________________________________________________ __________________________________ ___________________

PART NUMBER

MANUFACTURER

DESCRIPTION

IRF7413

11m? 8-pin SO, 30V

IRF7401

22m? 8-pin SO, 20V

IRL3502S

International Rectifier

6m? D

PAK, 20V

MMSF3300

20m? 8-pin SO, 30V

MMSF5N02H

30m? 8-pin SO, 20V

MTB60N05H

On Semiconductor

14m? D

PAK, 50V

FDS6670A

10m? 8-pin SO, 30V

ND8426A

13.5m? 8-pin SO, 20V

FDB8030L

Fairchild Semiconductor

4.5m? D

PAK, 30V

Table 6. Recommended n-Channel MOSFETs

COMPONENT

MANUFACTURER

PHONE

WEBSITE

Vishay/Dale Resistors

402-564-3131

www.vishay.com

Sense Resistors

IRC, Inc.

361-992-7900

www.irctt.com

International Rectifier

310-322-3331

www.irf.com

Fairchild Semiconductor

888-522-5372

www.fairchildsemi.com

MOSFETs

On Semiconductor

602-244-6600

www.onsemi.com

Table 7. Component Manufacturers

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