SP2526 Datasheet, PDF (7/18 Pages) Sipex Corporation – +3.0V to +5.5V USB Power Control Switch

minimum current of 0.5A to be delivered.
The SP2526 MOSFET switches will exhibit
very low resistance (<100mΩ) or voltage drop
until the current limit is reached. The fold back
current is the current that is delivered into a short
circuit at the output.
If the SP2526 MOSFET switch is enabled into a
heavy load or short-circuit, the switch will im-
mediately go into a constant-current mode, re-
ducing the output voltage. The respective fault
flag will pull low until the condition is removed.
When a heavy load is connected to the SP2526
switch output, a large transient current may flow
until the current limiting circuitry responds.
The SP2526 will provide a low resistance switch
(100mΩ) between the input and output pins.
This low resistance will be maintained with
increasing current until the 2.2A limit is reached.
If load current exceeds this limit, the switch will
increase its resistance. The foldback current
(500mA minimum) is reached when there is a
short applied to the output. The 100mΩ switch
resistance is guaranteed for all load currents,
increasing or decreasing, that are below 500mA.
Thermal Shutdown
Under nominal load conditions, the switch resis-
tance is very low and internal power dissipation
is low. Under short circuit conditions, current is
limited and internal power dissipation is higher
but not extreme. Under intermediate load condi-
tions, both the voltage across the switch and the
current through the switch are at intermediate
values and internal power dissipation is highest.
In this last condition, the die temperature will
reach the thermal limit and the switches in both
channels will be shut off. As the die subse-
quently cools, the switch will turn on again. If
the load is not removed, the device will thermal
cycle in this manner to protect itself from dam-
age.
Thermal shutdown is asserted if the die tempera-
ture exceeds 135^OC and will not release until the
die termperature drops below 125^OC. Thermal
shutdown will disable both output MOSFET
switches and force both FLGA and FLGB fault
flags low.
The delay between a current limit fault and
thermal shutdown will vary with ambient tem-
perature, board layout, and load impedance, but
is typically several hundred milliseconds. A
designer
can command a USB controller to recognize the
fault and disable the appropriate channel within
this time.
TYPICAL APPLICATIONS
Bypass Capacitors
A 0.1µF to 1.0µF bypass capacitor from the IN
pin to the GND pin is recommended to control
power supply transients. Refer to Figure 4.
Without a bypass capacitor, an output short may
cause sufficient ringing and damage the device.
Without a bypass capacitor, excessive supply
lead inductance is also a concern.
Input or output transients must not exceed the
absolute maximum supply voltage of V =
IN(MAX)
+6.0V even for a short duration to avoid risk of
damage to the device.
Transient Overcurrent Filter
When the SP2526 is enabled, large values of
capacitance at the output of the device will cause
inrush current to exceed the short circuit current-
limit threshold of the device and assert a flag
fault condition for FLGA and/or FLGB. The
duration of this time will depend on the size of
the output capacitance. During the capacitance
charging time, the device enters into foldback
mode. As the capacitance is charged, the current
decreases below the current-limit threshold and
the fault flags that are present at the FLGA and/
or FLGB pins will then be deasserted.
In USB applications, it is required that output
bulk capacitance is utilized to support hot-plug
occurences. When the SP2526 is enabled, the
flag may go active for about 1ms due to inrush
current exceeding the current-limit setpoint.
Additionally, during hot-plug events, inrush cur-
rents may also cause the fault flags at the FLGA
and/or FLGB pins to go active. Since these
conditions are not valid overcurrent faults, the
USB controller must ignore the fault flags during
these events. To prevent this, a 1ms RC filter can
be implemented as shown in Figure 5. Alterna-
Rev. 8/21/01
SP2526 +3.0V to +5.5V USB Power Control Switch
7
© Copyright 2001 Sipex Corporation