Single 1.2A USB Switch in

3mm x 3mm TDFN

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9

Thermal Shutdown

When the MAX8586 die temperature exceeds +160°C,

the switch turns off and FAULT goes low. Thermal shut-

down does not utilize the 20ms fault-blanking timeout

period. When the junction temperature cools by 15°C,

the switch turns on again and FAULT returns high.

When an overload condition persists, the switch cycles

on and off, resulting in a pulsed output that reduces the

average system load.

Applications Information

Setting the Current Limit

A resistor from ISET to ground programs the current-

limit value. Use a resistor between 26k

Ω and 60kΩ to

set the current limit according to the formula:

Ω because the maxi-

mum current rating of the device may be exceeded.

Ω are not recommended

and do not provide a lower limit current than 500mA. If

the output drops below 1V (typ), the MAX8586 shifts to a

short-circuit current-limit threshold that is 30% above the

Input Power Supply and Capacitance

To limit the input voltage drop during momentary output

load transients, connect a capacitor from IN to ground.

A 1µF ceramic capacitor is required for local decou-

pling; however, higher capacitor values further reduce

the voltage drop at the input. When driving inductive

loads, a larger capacitance may be needed to prevent

voltage spikes from exceeding the MAX8586’s absolute

maximum ratings.

Output Capacitance

A capacitor as large as 500µF is allowed on the output

to smooth out transients and/or increase rise/fall times.

Larger output capacitance may be used, but the result-

ing output charge time during startup may exceed the

fault-blanking period resulting in a FAULT flag.

Driving Inductive Loads

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

and printers) typically connect to the USB port with

cables, adding an inductive component to the load. This

inductance causes the output voltage at the USB port to

oscillate during a load step. The MAX8586 drives induc-

tive loads; however, care must be taken to avoid

exceeding the device’s absolute maximum ratings.

Usually, the load inductance is relatively small, and the

MAX8586’s input includes a substantial bulk capaci-

tance from an upstream regulator as well as local

bypass capacitors, limiting overshoot. If severe ringing

occurs because of large load inductance, clamp the

MAX8586 output below +6V and above -0.3V.

Turn-On and Turn-Off Behavior

The MAX8586 features a slow turn-on and turn-off, mini-

mizing loading transients on the upstream power

source. SEL sets the active polarity of the logic inputs of

the MAX8586. Drive ON to the same logic state as SEL

to enable the output. Drive ON to the opposite logic

state as SEL to disable the output (see Table 1). The

output enters a high-impedance state when disabled.

Layout and Thermal Dissipation

Keep all input/output traces as short as possible to

reduce the effect of undesirable parasitic inductance

and optimize the switch response time to output short-

circuit conditions. Place input and output capacitors no

more than 5mm from device leads. Connect IN and OUT

to the 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 mini-

mal change in package temperature. Calculate the

power dissipation for this condition as follows:

maximum on-resistance of the switch (95m

Ω), the

power dissipation is:

Ω = 24mW

The worst-case power dissipation occurs when the out-

put current is just below the current-limit threshold with

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

power dissipated in the switch is the voltage drop

across the switch multiplied by the current limit:

For a 5.5V input and 1V output, the maximum power

dissipation is:

P = 1.6A x (5.5V - 1V) = 7.2W

SEL

ON

OUT STATE

High

High

Enabled

High

Low

Disabled

Low

High

Disabled

Low

Low

Enabled

Table 1. SEL/ON Inputs