Dual-Input, Dual-Output Load Switch
Functional Block Diagram
INA
I
LIM
UVLO
OTMP
UVLO
I
LIM
Slew
Rate
Slew
Rate
AAT4670
OUTA
EN
INB
OUTB
FAULTA
FAULTB
GND
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 from 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
microsecond, easing requirements on the input
capacitors. With such fast transient response time,
the upstream power supply rail is naturally isolated
from the protected port.
The AAT4670 is internally protected from thermal
damage by an over-temperature detection circuit. If
4670.2006.09.1.4
a high ambient temperature or an over-current con-
dition causes the die temperature to reach the inter-
nal 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 con-
ductivity of silicon and the size of the die, the tem-
perature across the die is relatively uniform at high
temperatures; therefore, as a precaution, both power
devices are switched off when the thermal threshold
is reached. Since the power devices operate from
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 appro-
priate channel. A thermal limit condition is reported
by both FAULT outputs. A three millisecond blanking
interval prevents false reporting during the charging
of a capacitive load, which typically 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.
7
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
