AAT4670 Datasheet, PDF (6/12 Pages) Advanced Analogic Technologies – Dual-Input, Dual-Output Load Switches

AAT4670
Dual-Input, Dual-Output Load Switches
Functional Block Diagram
INA
OUTA
I_LIM
Slew
Rate
UVLO
OTMP
EN
UVLO
I_LIM
Slew
Rate
INB
OUTB
FAULTA
FAULTB
Functional Description
The AAT4670 dual channel load switch, implement-
ed with isolated independent P-channel MOSFET
devices, is ideal for applications where dual power
supplies are in continuous use. Typical applications
for this include products with multiple USB ports, or
ports requiring protection that operate off of separate
power supplies. The input power supplies can be
any voltage between 2.2V and 5.5V in any combina-
tion; one supply is not required to be the higher volt-
age. Internally, the power supply for the control cir-
cuitry will automatically switch to the higher of the two
supplies. In the case where the supplies are equal,
+/- 30mV of hysteresis prevents the internal supply
from oscillating between the two input supplies. The
low impedance P-channel MOSFET devices are
identical in size allowing for layout flexibility. They are
controlled by a patented fast acting current loop, and
respond to short circuits in a fraction of a microsec-
ond, which eases requirements on the input capaci-
tors. With such fast transient response time, the
upstream power supply rail is naturally isolated from
the protected port. The AAT4670 is internally pro-
tected from thermal damage by an over temperature
detection circuit. If a high ambient temperature or an
6
GND
over current condition causes the die temperature to
reach the internal thermal limit, both power devices
are switched off until the die temperature cools to a
level below the thermal limit threshold. The device
will thermal cycle indefinitely until the over current or
high temperature condition is removed. Due to the
high thermal conductivity of silicon and the size of the
die, the temperature across the die is relatively uni-
form at high temperatures, and therefore, as a pre-
caution, both power devices are switched off when
the thermal threshold is reached. Since the power
devices operate off of independent power supplies,
independent under voltage lockout circuits are
employed. If the power supply to one channel falls
below the under voltage lockout threshold, the other
channel will remain active. A current limit condition is
reported by the open drain FAULT output associated
with the appropriate channel. A thermal limit condi-
tion is reported by both FAULT outputs. A three mil-
lisecond blanking interval prevents false reporting
during the charging of a capacitive load, which typi-
cally occurs during device turn-on, but may also
occur during a port hot plug-in event.
The AAT4670 is ideally suited for protection of periph-
eral ports such as USB, PS2 and parallel ports.
4670.2002.1.0.92