Datasheet

C
L
cap
C
IN
cap
2
IR ON
P I R= ´
J(max) A
D(max)
JA
T T
P
-
=
Q
TPS22930
www.ti.com SLVSBL3 –NOVEMBER 2012
BOARD LAYOUT AND THERMAL CONSIDERATIONS
For best performance, all traces should be as short as possible. To be most effective, the input and output
capacitors should be placed close to the device to minimize the effects that parasitic trace inductances may have
on normal operation. Using wide traces for VIN, VOUT, and GND helps minimize the parasitic electrical effects
along with minimizing the case to ambient thermal impedance.
The maximum IC junction temperature should be restricted to 125°C under normal operating conditions. To
calculate the maximum allowable dissipation, P
D(max)
for a given output current and ambient temperature, use the
following equation as a guideline:
(1)
Where:
P
D(max)
= maximum allowable power dissipation
T
J(max)
= maximum allowable junction temperature (125°C for the TPS22930)
T
A
= ambient temperature of the device
Θ
JA
= junction to air thermal impedance. See Thermal Information section. This parameter is highly
dependent upon board layout.
The power dissipated by the device depends on the R
ON
of the device at a given V
IN
. To calculate the amount of
power being dissipated by the device, use the following equation:
(2)
Where:
P
IR
= power dissipated by the device
I = load current in amperes
R
ON
= resistance of the device in Ohms at a given V
IN
(see Electrical Characteristics section)
The result from Equation 2 should always be less than or equal to the result from Equation 1.
The figure below shows an example of a layout.
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