AAT4685 Datasheet, PDF (9/17 Pages) Skyworks Solutions Inc. – thermal shutdown protection

Functional Block Diagram
DATA SHEET
AAT4685
Over-Voltage Protection Switch with OCP and BOVP
IN
OVP
POK
OCP
EN
OVP
Switch
UVLO
V_REF
POK
Detect
INT_VP
OCP
CP
Driver
INT
Regulator
INT_VP
POR
Bias ^VREF
and BG
Control
and Timer
INT_VP
V_REF
INT_VP
OUT
FLT
BOVP
OTP
option
GND
Functional Description
The AAT4685 provides up to 28V over-voltage and over-
current protection when powering low-voltage systems
such as cell phones, MP3, and PDAs or when charging
Lithium Ion batteries from a badly regulated supply. The
AAT4685 is inserted between the power supply or char-
ger source and the load to be protected. The AAT4685 IC
consists of a low resistance OVP switch, under-voltage
lockout protection, over-voltage monitor and protection,
over-current protection, battery over-voltage protection,
fast shut-down circuitry and a fault output flag.
In normal operation the OVP switch acts as a slew-rate
controlled load switch, connecting and disconnecting the
power supply from IN to OUT. A low resistance N chan-
nel MOSFET is used as to minimize the voltage drop
between the voltage source and the load and to reduce
the power dissipation.
When the voltage on the input exceeds the programmed
over-voltage trip point, the device immediately turns off
the internal OVP switch disconnecting the load from the
abnormal voltage, preventing damage to any down-
stream components. In the case of an over current con-
dition, it limits the system current at the threshold value,
and if the over current persists, the OVP switch is turned
off after a blanking period. If the battery voltage rises to
an unsafe level (BOVP threshold), the IC disconnects
OUT from the charging input power IN until the battery
voltage returns to an acceptable value. BOVP or OCP
blanking time ignores short time transients of over-bat-
tery voltage and overload current. Additionally, AAT4685
also monitors its own die temperature and turns the OVP
switch off if it becomes too hot.
The AAT4685 has a fault flag (FLT) pin to indicate the
fault conditions of input power over-voltage, load current
over-current, battery over-voltage, and over-tempera-
ture by pulling the flag signal down to alert the system.
If an input over-voltage condition or over-voltage battery
condition exists at the time of the device enable, then
the OVP switch will remain OFF and FLT is always low.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201960A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 16, 2012
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