1A Current-Limited Switch for 2 USB Ports

outputs. Input voltage glitches less than 150mV do not

cause a spurious

OC output. Load-transient faults less

than 10ms (typ) will not cause an

OC output assertion.

Only current-limit faults are blanked. Die overtempera-

ture faults and input voltage droops below the UVLO

threshold will cause an immediate

OC 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 (Figure 2).

Output Capacitor

Connect a 0.1µF capacitor from OUT to GND. This

capacitor helps to prevent inductive parasitics from

pulling OUT negative during turn-off.

Layout and Thermal Dissipation

Important: Optimize the switch response time to output

short-circuit conditions by keeping all traces as short

as possible to reduce the effect of undesirable parasitic

inductance. Place input and output capacitors as close

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

IN and OUT pins must be connected with short traces

to the power bus. Wide power-bus planes provide

superior heat dissipation through the MAX1922’s IN

and OUT pins. Under normal operating conditions, the

package can dissipate and channel heat away.

Calculate the maximum power dissipation as follows:

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

iting activates and the voltage drop across the switch

equals the input supply voltage. The power dissipated

across the switch increases, as does the die tempera-

ture. If the fault condition is not removed, the thermal-

overload protection circuitry activates (see

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.

Driving Inductive Loads

A wide variety of devices (mice, keyboards, cameras,

and printers) can load the USB port. These devices

commonly connect to the port with cables, which can

add an inductive component to the load. This induc-

tance causes the output voltage at the USB port to ring

during a load step. The MAX1922 is capable of driving

inductive loads, but avoid exceeding the device’s

absolute maximum ratings. Usually the load inductance

is relatively small, and the MAX1922 input includes a

substantial bulk capacitance from an upstream regula-

tor as well as local bypass capacitors, limiting over-

shoot. If severe ringing occurs due to large load

inductance, clamp the MAX1922 output below 6V and

above -0.3V.

Figure 2. Typical Application Circuit

MAX1922

IN

OUTPUT

OUT

INPUT

1

μF

0.1

μF*

*USB SPECIFICATIONS REQUIRE

A HIGHER VALUE CAPACITOR.

OVERCURRENT

OUTPUT

ON

100k

Ω

OFF

GND

OC

EN

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