MAX1558 Datasheet, PDF (9/12 Pages) Maxim Integrated Products – Dual, 3mm x 3mm, 1.2A/Programmable-Current USB Switches with Autoreset

Dual, 3mm x 3mm, 1.2A/Programmable-Current
USB Switches with Autoreset
Undervoltage Lockout and
Input Voltage Requirements
The MAX1558/MAX1558H include a UVLO circuit to
prevent erroneous switch operation when the input volt-
age is low during startup and brownout conditions.
Operation is inhibited when V_{IN_} is less than 2.5V.
Output-Current Fault Protection
The current limit for both switch outputs is programmed
by a resistor between 26kΩ and 60kΩ connected from
ISET to ground. See the Current-Limit Program Level vs.
R_ISET curve in the Typical Operating Characteristics and
Setting the Current Limit in the Applications Information
section. The MAX1558 reduces the gate drive to the
MOSFET switch when the programmed current-limit value
is reached. If the current-limit program value is reached,
the part reduces gate drive to regulate at the current limit.
If the current limit persists for 20ms (typ), the output turns
off and the fault flag is set until the fault is removed, as
detected by the autoreset circuit.
When the the output drops below 1V (typ), the current
limit is set 30% above the programmed level and
pulsed. This lowers the RMS current for a short-circuit
condition, which reduces system load current and
power dissipation. If a short circuit persists for 20ms,
the output turns off and the fault flag is set. The autore-
set circuit automatically restarts the part if the fault is
removed.
Fault Blanking
The MAX1558/MAX1558H switches can reach current
limit in normal operation when powering up or driving
heavy capacitive loads. To differentiate these conditions
from short circuits or sustained overloads, the
MAX1558/MAX1558H have independent fault-blanking
circuits in each switch. When a load transient causes
the device to enter the current limit, an internal counter
monitors the duration of the fault. For load faults exceed-
ing the 20ms fault-blanking time, the offending switch
turns off, the corresponding FLT_ signal asserts low,
and that channel enters autoreset mode (see the
Autoreset Mode section). Only current-limit and short-
circuit faults are blanked. Thermal-overload faults and
input-voltage drops below the UVLO threshold immedi-
ately cause the switch to turn off and FLT_ to assert low.
Fault blanking allows the MAX1558 to handle USB
loads that may not be fully compliant with USB specifi-
cations. USB loads with additional bypass capacitance
and/or large startup currents can be successfully pow-
ered even while protecting the upstream power source.
No fault is indicated if the switch is able to bring up the
load within the 20ms blanking period.
Autoreset Mode
If an output fault is detected for more than the 20ms
blanking time, the output latches off and the FLT_ out-
put goes low. The MAX1558/MAX1558H then source
30mA to the faulted output and monitor the output volt-
age to determine when the overload is removed. If the
voltage on the output rises above 0.5V for more than
20ms, the fault resets and the output turns on. The
MAX1558 can also be reset from fault manually by tog-
gling ON_ (ON_ for the MAX1558H) for that channel.
Reverse Current Blocking
The USB specification does not allow an output device
to source current back into the USB port. However, the
MAX1558/MAX1558H 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
MAX1558/MAX1558H are bidirectional switches.
Thermal Shutdown
The MAX1558/MAX1558H feature independent thermal
shutdown for each switch channel, allowing one switch
to deliver power even if the other switch has a fault con-
dition. When the junction temperature exceeds +160°C,
the switch turns off and the FLT_ output goes low imme-
diately; fault blanking does not occur during thermal
limit. When the junction cools by 10°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.
Fault Indicators
The MAX1558/MAX1558H provide an open-drain fault
output (FLT_) for each switch. For most applications, con-
nect FLT_ to IN_ through a 100kΩ pullup resistor. FLT_
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 20ms fault-blanking period is exceeded.
• The switch is in autoreset mode.
After the fault condition is removed, the FLT_ output
deasserts after a 20ms delay. Ensure that the
MAX1558/MAX1558H have adequate input bypass
capacitance to prevent glitches from triggering FLT_ out-
puts. Glitches that cause the input supply to drop below
2.5V may cause the undervoltage lockout to trigger, turn-
ing the outputs off and asserting the FLT signals.
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