Ω,

corresponding to a 4A current limit. Set the continuous

current-limit value 20% to 30% higher than the expect-

ed load current to ensure that normal conditions do not

trigger nuisance fault outputs. The short-circuit current

limit is internally set to 1.3 times the continuous current-

limit setting.

On/Off Control and UVLO

The MAX1562 has an active-low ON polarity and the

MAX1562H has an active-high ON polarity. SEL sets the

active polarity of the MAX1563. Connect ON to the same

voltage as SEL to enable OUT. Connect ON to the

opposite voltage as SEL to disable OUT (see Table 1).

The MAX1562/MAX1562H/MAX1563 include a UVLO

circuit to prevent erroneous switch operation when the

input voltage goes low during startup and brownout

conditions. Input voltages of less than +3.4V inhibit

operation of the device. FAULT asserts low during a

UVLO condition.

Output Fault Protection and Autoreset

The MAX1562/MAX1562H/MAX1563 sense the switch

output voltage and select continuous current limiting for

device operates in a continuous current-limit mode that

limits output current to the programmed current limit

ates in short-circuit current-limit mode, sourcing a

pulsed current to the load. The pulse current depends

on the programmed current-limit value, typically 30%

higher than the programmed current limit.

When either fault condition persists for 20ms, the output

turns off and the fault flag asserts. The output automati-

cally restarts when the short or overload is removed. Note

that during severe short conditions, FAULT does not wait

20ms but goes low immediately since there is typically

also an undervoltage transient during a severe short.

The MAX1562/MAX1562H/MAX1563 detect short-circuit

removal by sourcing 25mA from the output and monitor-

ing the output voltage. When the voltage at the output

exceeds +0.5V for 20ms, the fault flag resets, the output

turns back on, and the 25mA current source turns off.

Thermal Shutdown

When the MAX1562/MAX1562H/MAX1563 die tempera-

ture exceeds +160°C, the switch turns off and FAULT

goes low. Thermal shutdown does not utilize the 20ms

fault-blanking timeout period. When the junction tem-

perature cools by 15°C, the switch turns on again and

FAULT returns high. The switch cycles on and off if an

overload condition persists, resulting in a pulsed output

that reduces the average system load.

Fault Indicators

The MAX1562/MAX1562H/MAX1563 provide an open-

drain fault output, FAULT. Connect FAULT to IN through

a 100k

Ω 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 more than 20ms.

The FAULT output deasserts after a 20ms delay once the

fault condition is removed. Ensure that the MAX1562/

MAX1562H/MAX1563 input bypass capacitance is suffi-

ciently large to prevent load glitches from triggering the

FAULT output. Limit the input-voltage slew rate to

0.2V/µs to prevent erroneous FAULT indications.

To differentiate large capacitive loads from short circuits

or sustained overloads, the switches have a fault-blank-

ing circuit. When a load transient causes the device to

enter current limit, an internal counter monitors the dura-

tion of the fault. For load faults exceeding the 20ms

fault-blanking time, the switch turns off, FAULT asserts

low, and the device enters autoreset mode (see the

Output Fault Protection and Autoreset section). Only

current-limit and short-circuit faults are blanked. If ther-

mal-overload faults or the input voltage drops below the

UVLO threshold, the switch turns off and asserts FAULT

low immediately. Note that during severe short condi-

tions, FAULT goes low immediately since there is typi-

cally also a brief undervoltage transient.

Fault blanking allows the MAX1562/MAX1562H/

MAX1563 to handle USB loads that might not be fully

compliant with the USB specifications. These switches

successfully power USB loads with additional bypass

capacitance and/or large startup currents while pro-

tecting the upstream power source. No fault is reported

if the switch brings up the load within the 20ms blank-

ing period. See Table 2 for a summary of current-limit

and fault behavior.

Programmable 4A USB Current-Limited

Switches with Autoreset and Fault Blanking

8

_______________________________________________________________________________________

Table 1. On/Off Control

SEL

ON

OUT BEHAVIOR

GND

ON

GND

OFF

GND

OFF

ON