MAX5909EEE+【PDF 11/24 页】IC HOT-SWAP CTRLR DUAL 16QSOP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录43

7页 8页 9页 10页 [11页]12页 13页 14页 15页

Slow-Comparator Startup Period

The slow comparator is disabled during the startup

period while the external MOSFETs are turning on.

Disabling the slow comparator allows the device to

ignore the higher-than-normal inrush current charging

the board capacitors when a card is first plugged into a

live backplane.

Slow-Comparator Normal Operation

After the startup period is complete the slow compara-

tor is enabled and the device enters normal operation.

The comparator threshold voltage (V

SC,TH)

is fixed at

25mV for the MAX5904/MAX5905 and is adjustable

from 25mV to 100mV for the MAX5906MAX5909. The

slow-comparator response time decreases to a mini-

mum of 110祍 with a large overdrive voltage (Figure 9).

Response time is 3ms for a 1mV overdrive. The variable

speed response time allows the MAX5904MAX5909 to

ignore low-amplitude momentary glitches, thus increas-

ing system noise immunity. After an extended overcur-

rent condition, a fault is generated, PGOOD is pulled

low, and the MOSFET gates are discharged with a

strong 3mA pulldown current.

Fast-Comparator Startup Period

During the startup period the fast comparator regulates

the gate voltage to ensure that the voltage across the

sense resistor does not exceed V

SU,TH

. The startup

fast-comparator threshold voltage (V

SU,TH

) is scaled to

two times the slow-comparator threshold (V

SC,TH

Fast-Comparator Normal Operation

In normal operation, if the load current reaches the fast-

comparator threshold, a fault is generated, PGOOD is

pulled low, and the MOSFET gates are discharged with

a strong 3mA pulldown current. This happens in the

event of a serious current overload or a dead short. The

fast-comparator threshold voltage (V

FC,TH

) is scaled to

four times the slow-comparator threshold (V

SC,TH

). This

comparator has a fast response time of 260ns (Figure 9).

Undervoltage Lockout (UVLO)

The undervoltage lockout prevents the MAX5904

MAX5909 from turning on the external MOSFETs until

one input voltage exceeds the UVLO threshold (2.4V)

for t

D,UVLO

. The MAX5904MAX5909 use power from

the higher input voltage rail for the charge pumps. This

allows for more efficient charge-pump operation. The

UVLO protects the external MOSFETs from an insuffi-

cient gate drive voltage. t

D,UVLO

ensures that the board

is fully inserted into the backplane and that the input

voltages are stable. Any input voltage transient on both

supplies below the UVLO threshold will reinitiate the

D,UVLO

and the startup period.

Latched and Autoretry Fault Management

The MAX5905/MAX5907/MAX5909 latch the external

MOSFETs off when a fault is detected. Toggling ON

below 0.4V or one of the supply voltages below the

UVLO threshold for at least 100祍 clears the fault latch

and reinitiates the startup period. Similarly, the

MAX5904/MAX5906/MAX5908 turn the external

MOSFETs off when a fault is detected then automatical-

ly restart after the autoretry delay that is internally set to

64 times t

START

. During the autoretry delay, toggling

ON below 0.4V does not clear the fault. The autoretry

can be overridden causing the startup period to begin

immediately by toggling one of the supply voltages

below the UVLO threshold.

Low-Voltage, Dual Hot-Swap Controllers/Power

Sequencers

______________________________________________________________________________________ 11

4.8V TO 5.8V

GATE

PGOOD

OUT

LOAD

START

+ t

PGDLY

BOARD

= LARGE

BOARD

= 0

SU,TH

SENSE

Figure 2. Startup Waveforms

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式