AAT4672ITP-T1 ANALOGICTECH [Advanced Analogic Technologies], AAT4672ITP-T1 Datasheet - Page 9

• Manufacturer Part Number: AAT4672ITP-T1
• Description: Power Supply Selector Switch
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

input current surges from low impedance sources such
as batteries in portable devices.
Output Capacitor
A 1µF or greater capacitor is required between OUT and
GND (C
cific capacitor ESR requirement. If desired, C
increased to accommodate any load transient condition.
EN Input
The AAT4672 is enabled when V
conversely, the AAT4672 is disabled when V
(logic ‘1’).
PWRSEL Input
When V
limit is 20% of the current limit value programmed by
R
current limit is 100% of the current limit value pro-
grammed by R
Current Limit Resistor Selection
The current limits for power supply 1 and power supply
2 inputs are set by resistors between I
The following equation can be used to select the appro-
priate resistor for a particular current limit:
Design Example
A particular application requires that the current limit for
MAIN be set to 2A and the current limit for AUX be set
to 0.2A. What value of resistor is required for the IMAIN
and IAUX pins respectively?
SmartSwitch
I
V
R
200k
4672.2008.04.1.0
CLIMAIN/AUX
IAUX
IMAIN/IAUX
IMAIN/IAUX
; when V
OUT
PWRSEL
). As with the input capacitor, there is no spe-
respectively
on the IMAIN and IAUX pins respectively
Current limit for MAIN and/or AUX pins
Internally Regulated Voltage [0.5V ± 20%]
IMAIN and/or IAUX Resistor
Internal Gain Factor
I
CLMAIN/AUX
is ≤ 0.4V (logic ‘0’) the AUX-OUT current
PWRSEL
IAUX
TM
.
is ≥ 1.6V (logic ‘1’), the AUX-OUT
=
⎛
⎝
V
R
IMAIN/IAUX
IMAIN/IAUX
EN
⎞
⎠
is ≤ 0.4V (logic ‘0’);
· 200k
MAIN
/I
AUX
EN
OUT
w w w . a n a l o g i c t e c h . c o m
and GND.
is ≥ 1.6V
may be
For MAIN (power supply 1 input):
For AUX (power supply 2 input):
Thermal Considerations
Since the AAT4672 has an internal current limit and over-
temperature protection(thermal shutdown), junction tem-
perature is rarely a concern. However, if the application
requires large currents in a high temperature environ-
ment, it is possible that temperature rather than current
limit will be the dominant regulating condition. In these
applications, the maximum current available without risk
of an over-temperature condition must be calculated. The
maximum internal temperature while current limit is not
active can be calculated using Equation 1 (Eq. 1).
Eq. 1: T
In Equation 1, I
the load. R
AAT4672 at high temperatures (consult the “R
Temperature”
Characteristics” section of this datasheet). For estimat-
ing the R
Temperature” performance graph and increase the value
from the performance graph by 50%. R
resistance between the AAT4672 die and the printed
circuit board (PCB) onto which it is mounted; R
thermal resistance of the TSOPJW-12 package. T
the maximum ambient temperature that the PCB under
the AAT4672 would be if the AAT4672 were not dissipat-
ing power. Equation 1 can be rearranged to solve for I
into Equation 2 (Eq. 2).
J(MAX)
R
R
IAUX
DS(ON)(MAX)
DS(ON)(MAX)
IMAIN
= I
=
=
= 500kΩ (499.9kΩ standard value)
=
=
= 50kΩ (49.9kΩ standard value)
⎛
⎝
⎛
⎝
Power Supply Selector Switch
MAX
performance
MAX
0.5V
0.2A
I
⎛
⎝
⎛
⎝
V
CLAUX
0.5V
I
V
CLMAIN
IAUX
2A
2 · R
is the maximum current required by
IMAIN
is the maximum rated R
⎞
⎠
PRODUCT DATASHEET
use the data on the “R
⎞
⎠
⎞
⎠
· 200k
⎞
⎠
DS(ON)(MAX)
· 200k
· 200k
· 200k
AAT4672
graph
· R
θJA
+ T
in
θJA
A(MAX)
is the thermal
the
DS(ON)
θJA
“Typical
DSON
DSON
A(MAX)
of the
is the
MAX
vs.
vs
is
9
,