MAX1940(2002) Ver la hoja de datos (PDF) - Maxim Integrated

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componentes Descripción

Fabricante

MAX1940
(Rev.:2002)

Triple USB Switch with Autoreset and Fault Blanking

Maxim Integrated 

Triple USB Switch with Autoreset and

Fault Blanking

INPUT

4V TO 5.5V

O.1µF

OFF

ON

MAX1940

IN1

FAULTA

IN2

FAULTB

IN3

FAULTC

IN4

IN5

OUTA

ONA

ONB

OUTB

ONC

SEL

OUTC

GND

100kΩ

100kΩ

100kΩ

USB

PORT A

1µF*

USB

PORT B

1µF*

USB

PORT C

1µF*

*USB APPLICATIONS MAY REQUIRE

ADDITIONAL BULK CAPACITANCE

Figure 2. Typical Application Circuit

power bus with short traces. Wide power bus planes at

IN_ and OUT provide superior heat dissipation as well.

An active switch dissipates little power with minimal

change in package temperature. Calculate the power

dissipation for this condition as follows:

P = (IOUT_)2 x RON

At the normal operating current (IOUT_ = 0.5A) and the

maximum on-resistance of the switch (135mΩ), the

power dissipation is:

P = (0.5A)2 x 0.135Ω = 34mW per switch.

The worst-case power dissipation occurs when the output

current is just below the current-limit threshold (1.2A max)

with an output voltage greater than 1V. In this case, the

power dissipated in each switch is the voltage drop

across the switch multiplied by the current limit:

P = ILIM x (VIN - VOUT)

For a 5V input and 1V output, the maximum power dis-

sipation per switch is:

P = 1.2A x (5V - 1V) = 4.8W

Because the package power dissipation is 667mW, the

MAX1940 die temperature exceeds the +160°C thermal

shutdown threshold, and the switch output shuts down

until the junction temperature cools by +15°C. The duty

cycle and period are strong functions of the ambient

temperature and the PC board layout (see the Thermal

Shutdown section).

If the output current exceeds the current-limit threshold,

or the output voltage is pulled below the short-circuit

detect threshold, the MAX1940 enters a fault state after

20ms, at which point autoreset mode is enabled and

25mA is sourced by the output. For a 5V input, OUT_

short-circuited to GND, and autoreset mode active, the

power dissipation is as follows:

P = 0.025A x 5V = 0.125W

Chip Information

TRANSISTOR COUNT: 4259

PROCESS: BiCMOS

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