Current-Limited Switch for Single USB Port

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7

spurious FAULT output. Load-transient faults less than

10ms (typ) do not cause a FAULT output assertion.

Only current-limit faults are blanked. Die overtempera-

ture faults and input voltage droops below the UVLO

threshold cause an immediate fault output.

Applications Information

Input Capacitor

To limit the input voltage drop during momentary output

short-circuit conditions, connect a capacitor from IN to

GND. A 1µF ceramic capacitor is adequate for most

applications; however, higher capacitor values further

reduce the voltage drop at the input (see Figure 2).

Output Capacitor

Connect a 0.1µF capacitor from OUT to GND. This cap-

acitor helps prevent inductive parasitics from pulling

OUT negative during turn-off.

Layout and Thermal Dissipation

To optimize the switch-response time to output short-

circuit conditions, it is very important to keep all traces

as short as possible to reduce the effect of undesirable

parasitic inductance. Place input and output capacitors

as close to the device as possible (no more than 5mm).

All IN and all OUT pins must be connected with short

traces to the power bus. Wide power bus planes pro-

vide superior heat dissipation through the switch IN and

OUT pins. Figure 3 shows suggested pin connections

for a single-layer board.

Under normal operating conditions, the package can

dissipate and channel heat away. Calculate the maxi-

mum power dissipation as follows:

Ω max).

When the output is short-circuited, foldback-current-lim-

iting activates and the voltage drop across the switch

equals the input supply. The power dissipated across

the switch increases, as does the die temperature. If the

fault condition is not removed, the thermal-overload pro-

tection circuitry activates (see the Thermal Shutdown

section). Wide power-bus planes connected to IN and

OUT and a ground plane in contact with the device

help dissipate additional heat.

1

2

3

4

5

10

9

8

7

6

OUT

IN

OUT

FAULT

OUT

IN

OUT

IN

MAX1931

GND

ON

Figure 3. IN and OUT Cross Connections for a Single-Layer

Board

Figure 2. Typical Application Circuit

Chip Information

TRANSISTOR COUNT: 715

MAX1931

IN

OUTPUT

OUT

INPUT

2.7V TO 5.5V

FAULT

ON

ON

OFF

100k

Ω

1

µF

0.1

µF*

*USB SPECIFICATIONS REQUIRE A LARGER CAPACITOR

GND