Current Limited Load Switch
AAT4618 would be if the AAT4618 were not dissi-
pating power. Equation 1 can be rearranged to
solve for I
MAX
, as shown in Equation 2.
For example, if an application is specified to oper-
ate in 50°C environments, the PCB operates at
temperatures as high as 85°C. The application is
sealed and its PCB is small, causing R
θJA
to be
approximately 150 °C/W. Using Equation 2,
AAT4618
Eq. 2:
I
MAX
=
T
SD(MIN)
- T
A(MAX)
R
DS(ON)(MAX)
· R
ΘJA
Eq. 3:
I
MAX
=
115 - 85
= 950mA
220
· 150
T
SD(MIN)
is the minimum temperature required to
activate the AAT4618 over-temperature protection.
With the typical specification of 125°C, 115°C is a
safe minimum value to use.
The AAT4618 is safe to operate at the minimum
current limit level of 500mA at 85°C.
4618.2006.05.1.2
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
