DATA SHEET • AAT4687 OVER-VOLTAGE PROTECTION SWITCH
Fixed Option
(metal programable)
IN
OUT
FLT
OVP
Sense
and
OVP
EN
Control
GND
tc240
Figure 21. AAT4687 Functional Block Diagram
MOSFET is turned off. Hysteresis of 100 mV is included to
ensure circuit stability.
Functional Description
The AAT4687 provides up to 28 V over-voltage protection when
powering low-voltage systems such as cell phones, MP3
players, and PDAs or when charging Lithium-Ion batteries from
a poorly regulated supply. The AAT4687 is inserted between the
power supply or charger source and the load to be protected.
The AAT4687 IC includes a low-resistance P-channel MOSFET,
under-voltage lockout protection, over-voltage monitor, fast
shut-down circuitry, and a fault output flag.
Over-Voltage Protection (OVP)
The AAT4687 adjustable version has a 1.1 V 1.5%
overvoltage trip threshold on the OVP pin. With a resistor
divider on the OVP pin from IN to GND, the over-voltage trip
point can be adjusted anywhere within the input voltage range
(see Table 5). Once the over-voltage trip level is triggered, the
PMOS switch controller will turn off the PMOS in less than
0.7 s.
In normal operation, the P-channel MOSFET acts as a slew-rate
controlled load switch, connecting and disconnecting the power
supply from IN to OUT. A low-resistance MOSFET is used to
minimize the voltage drop between the voltage source and the
load and to reduce power dissipation. When the voltage on the
input exceeds the over-voltage protection trip voltage (internally
set in the fixed voltage version or externally by a voltage divider
to the OVP pin for the adjustable version), the device
In the AAT4687 fixed version, the resistor divider is internally
integrated with the input voltage trip point at 6.5 V. The fixed
version of the AAT4687 does not have a connection to the
internal OVP circuitry, and Pin 1 is designed to be left
unconnected.
immediately turns off the internal P-channel FET, disconnecting
the load from the input and preventing damage to downstream
components. Simultaneously, the fault flag is raised, alerting
the system to a problem.
Over-Temperature Protection (OTP)
If the ambient temperature of the device exceeds TSHDN, the
OVP switch is turned off, and the pin is driven low. The OVP
switch recovers automatically when the junction temperature
falls below (TSHDN 20 °C).
If an over-voltage condition is applied at the time of the device
enable, then the switch will remain OFF.
Fault Indicator (FLT)
A functional block diagram is shown in Figure 21. Figure 22
shows the timing diagram.
The output is an active-low open-drain fault reporting output. A
pull-up resistor should be connected from FLT to the logic I/O
voltage of the host system. FLT is asserted immediately if an
over-voltage or over-temperature fault occurs.
Under-Voltage Lockout (UVLO)
The AAT4687 has a fixed 3.0 V under-voltage lockout level
(UVLO). When the input voltage is less than the UVLO level, the
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201962C • Skyworks Proprietary and Confidential Information • Products and Product Information are Subject to Change Without Notice • June 3, 2014
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