AAT4685 Datasheet, PDF (13/17 Pages) Skyworks Solutions Inc. – thermal shutdown protection

DATA SHEET
AAT4685
Over-Voltage Protection Switch with OCP and BOVP
Application Information
Over-Voltage Protection Resistors
The over-voltage protection threshold is programmed
with two resistors, R1 and R2. To limit the current going
through the external resistor string while maintaining
good noise immunity, use smaller resistor values, such as
10kΩ for R2. Using a larger value will further reduce the
system current, but will also increase the impedance of
the OVP node, making it more sensitive to external noise
and interference. A suggested value for R2 is 100kΩ. R1
can be calculated using the following equation:
R₁ =
V_OVP
V_{OVP_TH}
-1
· R₂
= (V_OVP -
1)
· 100
Table 1 summarizes 1% standard metal film resistors for
several over-voltage settings.
R2 (kΩ)
100
100
100
100
100
100
100
R1 (kΩ)
300
348
402
442
499
549
604
V_OVP Setting (V)
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Table 1: 1% Standard Resistor Values
for OVP Setting.
Over-Current Protection Resistor
The over-current threshold is programmed by an exter-
nal resistor (R_OCP) connected from the OCP pin to GND.
R_OCP can be calculated by the following equation.
30
R_OCP = _IOCP · 1000
Table 2 summarizes 1% standard metal film resistors for
several over-current settings.
R3 (kΩ)
100.0
86.6
75.0
66.5
60.4
54.9
49.9
43.0
37.4
33.2
30.1
24.9
21.5
18.7
16.5
I_OCP Setting (A)
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.70
0.80
0.90
1.00
1.20
1.40
1.60
1.80
Table 2: 1% Standard Resistor Values
for OCP Setting.
Input Capacitor
A 1μF or larger capacitor is typically recommended for
C_IN. C_IN should be located as close to the device IN pin as
practically possible. Ceramic, tantalum, or aluminum
electrolytic capacitors may be selected for C_IN. There is
no specific capacitor equivalent series resistance (ESR)
requirement for C_IN. However, for higher current opera-
tion, ceramic capacitors are recommended for C_IN due to
their inherent capability over tantalum capacitors to
withstand input current surges from low impedance
sources such as batteries in portable devices.
Capacitors are typically manufactured in different volt-
age ratings. If the maximum possible surge voltage is
known, select capacitors with a voltage rating at least 5V
higher than the maximum possible surge voltage. 50V
rated capacitors are generally good for most OVP appli-
cations to prevent any surge voltage.
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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