SP2026 Sipex, SP2026 Datasheet - Page 7

• Manufacturer Part Number: SP2026
• Description: +2.7V to +5.5V USB Power Control Switch
• Manufacturer: Sipex

The SP2026 MOSFET switches will exhibit
very low resistance (100m ) 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 SP2026 MOSFET switch is enabled into a
heavy load or short-circuit, the switch will imme-
diately go into a constant-current mode, reducing
the output voltage. The respective fault flag will
pull low until the condition is removed.
When a heavy load is connected to the SP2026
switch output, a large transient current may flow
until the current limiting circuitry responds.
The SP2026 will provide a low resistance switch
(100m ) between the input and output pins. This
low resistance will be maintained with increasing
current until the 1.25A limit is reached. If load
current exceeds this limit, the switches will in-
crease their resistance. The foldback current
(500mA minimum) is reached when there is a
short applied to either output. The 100m switch
resistance is guaranteed for all load currents, in-
creasing or decreasing, that are below 500mA.
Thermal Shutdown
Under nominal load conditions, the switch re-
sistances are very low and internal power dissi-
pation is low. Under short circuit conditions,
current is limited and internal power dissipation
is higher but not extreme. Under intermediate
load conditions, both the voltage across the
switch and the current through the switch are at
intermediate values and internal power dissipa-
tion 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 subsequently 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 damage.
The SP2026 has dual sensors to detect
overtemperature. If the die temperature reaches
140 C and channel A is in current limit, output
switch A is disabled and flag A is asserted.
Unless channel B current limits, switch B re-
mains enabled and flag B is not asserted. If the
die temperature reaches 140 C and channel B is
in current limit, output switch B is disabled and
flag B is asserted. Unless channel A current
limits, switch A remains enabled and flag A is
not asserted. If the die exceeds 160 C, both
Rev. 1/23/02
SP2026 +2.7V to +5.5V USB Power Control Switch
7
output switches are disabled and both flags are
asserted. A device is disabled in thermal shut-
down until the excessive current load is removed,
the appropriate enable pins are toggled, or the
temperature cools to 120 C.
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 0.1 F to 1.0 F 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 suffi-
cient ringing and damage the device. Without a
bypass capacitor, excessive supply lead induc-
tance is also a concern.
Input or output transients must not exceed the
absolute maximum supply voltage of V
+6.0V even for a short duration to avoid risk of
damage to the device.
Soft Start Condition
The soft start feature of the SP2026 is imple-
mented by holding the output turn-on rise time
to 1ms. When off, the device has high imped-
ance MOSFET channels that slowly become
low impedance as the device powers on. This
prevents an inrush current from causing voltage
drops that result from charging a capacitive load
and can pull the USB voltage bus below speci-
fied levels. This satisfies the USB voltage droop
requirements for bus-powered applications.
Refer to the circuit in Figure 6.
The SP2026 can provide inrush current limiting
for applications with large load capacitances where
C
a configuration that will meet USB transient regu-
lation specifications with large load capacitances.
Enable Input
The ENA and ENB control pins must be driven
to a logic high or logic low for a clearly defined
signal input. Floating these control lines may
cause unpredictable operation.
BULK
> 10 F. Refer to the circuit in Figure 7 for
© Copyright 2002 Sipex Corporation
IN(MAX)
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