MAX1562 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Programmable 4A USB Current-Limited Switches with Autoreset and Fault Blanking

Programmable 4A USB Current-Limited
Switches with Autoreset and Fault Blanking
For the MAX1563, the minimum R_ISET value is 4.22kΩ,
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
V_OUT greater than 1V or short-circuit current limiting for
V_OUT less than 1V. When V_OUT is greater than 1V, the
device operates in a continuous current-limit mode that
limits output current to the programmed current limit
(1A to 4A). When V_OUT is less than 1V, the device oper-
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.
Table 1. On/Off Control
SEL
GND
V_IN
ON
GND
V_IN
GND
V_IN
OUT BEHAVIOR
ON
OFF
OFF
ON
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 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 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.
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