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MAX8586

Single 1.2A USB Switch in 3mm x 3mm TDFN

Maxim Integrated 

MAX8586

Single 1.2A USB Switch in

3mm x 3mm TDFN

Detailed Description

Current-Limit Protection

The MAX8586 uses two methods to protect the circuit

from overcurrent conditions. Continuous current limiting

has tighter accuracy but slower response time com-

pared to short-circuit limiting. Combining both methods

provides a high degree of protection for a variety of

faults. When a current-limit fault occurs with VOUT

greater than 1V, the device operates in continuous cur-

rent-limit mode and limits output current to a user-pro-

grammable level. When VOUT is less than 1V, the

device operates in short-circuit current-limit mode and

pulses the output current to levels that are 30% (typ)

higher than the selected continuous current limit.

When either fault condition persists for 20ms (typ), the

fault flag is asserted. With the auto-restart enabled

(ENRESET high) the output also latches off and is test-

ed with a 25mA current to detect when the fault condi-

tion has been removed. 20ms after the fault condition is

removed, the output automatically restarts. With the

auto-restart disabled (ENRESET low), the output contin-

ues to source the current-limit current as long as the

fault is present.

Reverse Current Protection

The USB specification does not allow an output device

to source current back into the USB port. However, the

MAX8586 is designed to safely power noncompliant

devices. During normal operation with the channel

enabled, if the current from the output to the input

exceeds 1A (typ) for more than 20ms (typ), the IC turns

off the switch and the FAULT flag is asserted. When the

IC is disabled, the output is switched to a high-imped-

ance state, blocking reverse current flow from the out-

put back to the input.

On/Off Control and UVLO

The MAX8586 has a selectable active-high/low ON

polarity. Drive SEL high to select an active-high for ON;

drive SEL low to select active-low for ON. The

MAX8586 includes a UVLO circuit to prevent erroneous

switch operation when the input voltage goes low dur-

ing startup and brownout conditions. Input voltages of

less than +2.5V (typ) inhibit operation of the device.

FAULT asserts low during a UVLO condition.

Output Fault Protection and Auto-Restart

The MAX8586 uses an auto-restart function to detect

short-circuit removal by sourcing 25mA from the output

and monitoring the output voltage. When the voltage at

the output exceeds 0.5V for 20ms, the fault flag releases,

the output turns back on, and the 25mA current source

turns off. Active loads are not expected to draw measur-

able current when supplied with less than 0.5V. The auto-

restart function is enabled when ENRESET is high. Drive

ENRESET low to disable the auto-restart function. When

the auto-restart function is disabled, OUT regulates the

current to the programmed current limit.

Fault Indicator and Fault Blanking

The MAX8586 provides an open-drain output (FAULT)

to signal fault conditions. Connect FAULT to IN through

a 100kΩ pullup resistor for most applications. FAULT

asserts low when any of the following conditions occur:

• The input voltage is below the UVLO threshold.

• The switch junction temperature exceeds the

+160°C thermal-shutdown temperature limit.

• The switch is in current-limit or short-circuit current-

limit mode for longer than the fault-blanking period

(20ms typ).

• The reverse current exceeds the 1A threshold for

longer than the fault-blanking period (20ms typ).

When auto-restart is enabled, the FAULT output goes

high impedance after a 20ms delay once the fault con-

dition is removed. With auto-restart disabled, during the

fault the output is tested every 20ms. When the fault is

removed, the FAULT output goes high impedance after

a delay that can be up to 20ms. Ensure that the

MAX8586 input bypass capacitance prevents glitches

from triggering the FAULT output. To distinguish large

capacitive loads from short circuits or sustained over-

loads, the MAX8586 has a fault-blanking circuit. When

a load transient causes the output to enter current limit,

an internal counter monitors the duration of the fault.

For load faults exceeding the 20ms fault-blanking time,

the switch turns off, FAULT asserts low, and the output

enters auto-restart mode (see the Current-Limit

Protection and Output Fault Protection and Auto-Restart

sections). Only current-limit and short-circuit faults are

blanked. Thermal-overload faults and input voltages

below the UVLO threshold immediately turn the output

off and assert FAULT low.

Fault blanking allows the MAX8586 to handle USB

loads that might not be fully compliant with USB specifi-

cations. The MAX8586 successfully powers USB loads

with additional bypass capacitance and/or large start-

up currents while protecting the upstream power

source. No fault is reported if the switch brings up the

load within the 20ms blanking period.

8

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