MAX5904(2003) データシートの表示（PDF） - Maxim Integrated

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MAX5904
(Rev.:2003)

Low-Voltage, Dual Hot-Swap Controllers/Power Sequencers

Maxim Integrated 

Low-Voltage, Dual Hot-Swap Controllers/Power

Sequencers

PIN

MAX5904/

MAX5905

MAX5906–

MAX5909

—

10

5

11

6

12

7

13

8

14

—

15

—

16

Pin Description (continued)

NAME

FUNCTION

LIM2

ON

GATE2

SENSE2

IN2

INC+

OUTC

Channel 2 Current-Limit Setting. Connect a resistor from LIM2 to GND to set

current-trip level. Connect to GND for the default 25mV threshold.

On Comparator Input

Channel 2 Gate-Drive Output. Connect to gate of external N-channel MOSFET.

Channel 2 Current-Sense Input. Connect RSENSE2 from IN2 to SENSE2.

Channel 2 Supply Input. Connect to a supply voltage from 1V to 13.2V. Connect a

0.1µF ceramic bypass capacitor from IN2 to GND to filter high-frequency noise.

Uncommitted Comparator Noninverting Input

Uncommitted Comparator Open-Drain Output. Actively held low when VINC+ is less

than 1.236V.

Detailed Description

The MAX5904–MAX5909 are circuit breaker ICs for hot-

swap applications where a line card is inserted into a

live backplane. These devices hot swap supplies rang-

ing from +1V to +13.3V, provided one supply is at or

above 2.7V. Normally, when a line card is plugged into

a live backplane, the card’s discharged filter capacitors

provide low impedance that can momentarily cause the

main power supply to collapse. The MAX5904–

MAX5909 reside either on the backplane or on the

removable card to provide inrush current limiting and

short-circuit protection. This is achieved by using exter-

nal N-channel MOSFETs, external current-sense resis-

tors, and two on-chip comparators. Figure 1 shows the

MAX5906–MAX5909 functional diagram.

The MAX5904/MAX5905 have a fixed startup period

and current-limit threshold. The startup period and cur-

rent-limit threshold of the MAX5906–MAX5909 can be

adjusted with external resistors.

Startup Period

RTIM sets the duration of the startup period for the

MAX5906–MAX5909 from 0.4ms to 50ms (see the

Setting the Startup Period section). The duration of the

startup period is fixed at 9ms for the MAX5904/

MAX5905. The startup period begins after the following

three conditions are met:

1) VIN1 or VIN2 exceeds the UVLO threshold (2.4V) for

the UVLO to startup delay (37.5ms).

2) VON exceeds the channel 1 ON threshold (0.825V).

3) The device is not latched or in its auto-retry delay.

(See Latched and Auto-Retry Fault Management.)

The MAX5904–MAX5909 limit the load current if an

overcurrent fault occurs during startup. The slow com-

parator is disabled during the startup period and the

load current can be limited in two ways:

1) Slowly enhancing the MOSFETs by limiting the

MOSFET gate charging current

2) Limiting the voltage across the external current-

sense resistor.

During the startup period the gate drive current is typi-

cally 100µA and decreases with the increase of the

gate voltage (see Typical Operating Characteristics).

This allows the controller to slowly enhance the

MOSFETs. If the fast comparator detects an overcur-

rent, the MAX5904–MAX5909 regulate the gate voltage

to ensure that the voltage across the sense resistor

does not exceed VSU,TH. This effectively regulates the

inrush current during startup. Figure 2 shows the start-

up waveforms. PGOOD goes high impedance 0.75ms

after the startup period if no fault condition is present.

VariableSpeed/BiLevel Fault Protection

VariableSpeed/BiLevel fault protection incorporates two

comparators with different thresholds and response

times to monitor the load current (Figure 9). During the

startup period, protection is provided by limiting the

load current. Protection is provided in normal operation

(after the startup period has expired) by discharging

both MOSFET gates with a strong 3mA pulldown cur-

rent in response to a fault condition. After a fault,

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