Rainbow Electronics MAX1563 - Manual (Page 9)

Applications Information
Input Power Supply and Capacitance
Connect both IN inputs together externally. IN powers
the internal control circuitry and charge pump for the
switch, allowing a decreased R
ON
. Bypass IN to GND
with a 1µF ceramic capacitor. When driving inductive
loads or operating from inductive sources, which may
occur when the device is powered by long leads or PC
traces, larger input bypass capacitance is required to
prevent voltage spikes from exceeding the absolute
maximum ratings during short-circuit events.
Output Capacitor
Bypass OUT to GND with a 4.7µF ceramic capacitor for
local decoupling. Additional bulk capacitance (up to
470µF) reduces output-voltage transients under dynam-
ic load conditions. Using output capacitors greater than
470µF might assert FAULT if the current limit cannot
charge the output capacitor within the 20ms fault-
blanking period. In addition to bulk capacitance, small-
value (0.1µF or greater) ceramic capacitors improve the
output’s resilience to electrostatic discharge (ESD).
Driving Inductive Loads
A wide variety of devices (mice, keyboards, cameras,
and printers) typically connect to the USB port with
cables, which might add an inductive component to the
load. This inductance causes the output voltage at the
USB port to oscillate during a load step. The
MAX1562/MAX1562H/MAX1563 drive inductive loads,
but avoid exceeding the device’s absolute maximum
ratings. The load inductance is usually relatively small,
and the MAX1562/MAX1562H/MAX1563s’ input
includes a substantial bulk capacitance from an
upstream regulator, as well as local bypass capacitors,
limiting overshoot. If severe ringing occurs because of
large-load inductance, clamp the MAX1562/MAX1562H/
MAX1563 outputs below +6V and above -0.3V.
Turn-On and Turn-Off Behavior
When turned on, the MAX1562/MAX1562H/MAX1563 out-
put ramps up over 2.5ms to eliminate load transients on
the upstream power source. When turned off, the output
ramps down for 800µs. Under fault conditions, the output
of the switches turns off rapidly to provide maximum safe-
ty for the upstream power source and downstream
devices. Internal blocks shut down to minimize supply
current when the switch is off.
MAX1562/MAX1562H/MAX1563
Programmable 4A USB Current-Limited
Switches with Autoreset and Fault Blanking
_______________________________________________________________________________________ 9
Table 2. Current Limiting and Fault Behavior
CONDITION MAX1562/MAX1562H/MAX1563 BEHAVIOR
Output Short-Circuit
(V
OUT < +1V)
• If a short is detected at the output, the channel turns off, and the blanking timer begins. FAULT
remains high during the blanking timeout period.
• If the short persists during the fault-blanking period, the output pulses at 0.30 x I LIM RMS. If the short
is removed before the 20ms short-circuit blanking timeout period, the next ramped current pulse soft-
starts the output. FAULT remains high.
• If the short-circuit persists after the fault-blanking period. FAULT goes low, autoreset mode begins,
and the output sources 25mA.
• If the output voltage rises above 0.5V for 20ms, the channel resets, the output turns on, and FAULT
goes high.
Output Overload Current
(V
OUT > +1V)
• If an overload occurs, output current regulates at I LIM and the blanking timer turns on. FAULT remains
high during the blanking timeout period.
• Continuous current at I LIM persists until either the 20ms blanking period expires or a thermal
fault occurs.
• If overcurrent persists after 20ms, FAULT goes low, autoreset mode is enabled, and the output
sources 25mA.
• If the output voltage rises above 0.5V for 20ms, the channel resets, the output turns on, and
FAULT goes high (see the Overload Response into 1.4 Ω graph in the Typical Operating
Characteristics section).
Thermal Fault
(T
J > +160°C)
• A junction temperature of +160 o C immediately asserts FAULT low (the blanking timeout period
does not apply for thermal faults) and turns off the switch. When the junction cools by 15°C, the
thermal fault is cleared and FAULT goes high. Note that if other fault conditions are present when
a thermal fault clears, those fault states take effect.