MAX1823AEUB View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX1823AEUB

Dual USB Switch with Fault Blanking and Autoreset

Maxim Integrated 

Dual USB Switch with Fault

Blanking and Autoreset

Detailed Description

The MAX1823 is a dual, current-limited switch designed

for USB applications. It has two independent switches,

each with its own enable control input and autoreset

function. Each switch has an error-flag output to notify

the USB controller when the current-limit, short-circuit,

undervoltage-lockout, or thermal-shutdown threshold is

reached (Figure 2).

The MAX1823 operates from a 4V to 5.5V input voltage

range and guarantees a minimum 720mA output current.

A built-in 0.9A current limit limits the current in the event

of a heavy-overload condition. The MAX1823 has inde-

pendent thermal shutdown for each switch in the event

of a prolonged overload or short-circuit condition. The

autoreset function monitors the overload and automati-

cally turns the switch on when the overload is removed.

Use of low-RON NMOS switches enables the MAX1823

to provide two switches in the ultra-small 10-pin µMAX

package. An internal micropower charge pump gener-

ates the high-side supply needed for driving the gates

of these high-side switches. Separate current-limiting

and thermal-shutdown circuits permit each switch to

operate independently, improving system robustness.

Undervoltage-Lockout and

Input-Voltage Requirements

The MAX1823 includes a UVLO circuit to prevent erro-

neous switch operation when the input voltage goes

low during startup and brownout conditions. Operation

is inhibited when VIN_ is less than 3.4V.

Output Fault Protection

The MAX1823 senses the switch output voltage and

selects continuous current limiting when VOUT is greater

than 1V or short-circuit current limiting when VOUT is less

than 1V. When VOUT is greater than 1V, the device oper-

ates in a continuous current-limit mode that sets the out-

put current limit to 0.9A. When VOUT is less than 1V, the

device operates in short-circuit current-limit mode,

sourcing 0.35ARMS current pulses to the load.

Autoreset Mode

If an output fault is detected for more than the 20ms

blanking time, the output latches off, the FAULT_ output

goes low, and a 25mA current is forced at the output. If

the voltage on the output exceeds 0.5V for 20ms, the fault

resets, the 25mA current source shuts down, and the out-

put turns on. The device monitors the output voltage so

that a short-circuit condition can be detected. Active

loads are not expected to have measurable currents

when the supply is below 0.5V. The MAX1823/MAX1823A

can also be reset from fault manually by toggling ON_

(ON_ for the MAX1823B/MAX1823H) for that channel.

Thermal Shutdown

The MAX1823 features independent thermal shutdown

for each switch channel, allowing one switch to deliver

power even if the other switch has a fault condition.

When the junction temperature exceeds +160°C, the

switch turns off and the FAULT_ output goes low imme-

diately; fault blanking does not occur during thermal

limit. When the junction cools by 15°C, the switch turns

on again. If the fault overload condition continues, the

switch cycles on and off, resulting in a pulsed output,

saving battery power.

Reverse Current Blocking

The USB specification does not allow an output device

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

MAX1823A/MAX1823B are designed to safely power

noncompliant devices. When disabled, each output is

switched to a high-impedance state, blocking reverse

current flow from the output back to the input. However,

during normal operation with the device enabled, the

MAX1823A/MAX1823B are bidirectional switches.

Fault Indicators

The MAX1823 provides an open-drain fault output

(FAULT_) for each switch. For most applications, connect

FAULT_ to IN_ through a 100kΩ pullup resistor. FAULT_

goes 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 limit

mode after the fault-blanking period is exceeded.

• The switch is in autoreset mode.

INPUT

4V TO 5.5V

0.1µF

100kΩ

100kΩ

INA

OUTA

IN

INB

MAX1823

FAULTA

OUTB

FAULTB

ONA

ONA

ONB

ONB GND

* USB APPLICATIONS MAY REQUIRE

ADDITIONAL BULK CAPACITANCE.

Figure 1. Typical Application Circuit

USB

PORT A

1µF*

USB

PORT B

1µF*

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