AP2280
Single Channel Slew Rate Controlled Load Switch
AP2280 Rev. 6
8 of 12 FEBRUARY 2009
www.diodes.com © Diodes Incorporated
Input Capacitor
A 1μF capacitor is recommended to connect
between IN and GND pins to decouple input power
supply glitch and noise. The input capacitor has no
specific type or ESR (Equivalent Series Resistance)
requirement. However, for higher current
application, ceramic capacitors are recommended
due to their capability to withstand input current
surges from low impedance sources, such as
batteries in portable applications. This input
capacitor must be located as close as possible to
the device to assure input stability and less noise.
For PCB layout, a wide copper trace is required for
both IN and GND.
Output Capacitor
A 0.1μF capacitor is recommended to connect
between OUT and GND pins to stabilize and
accommodate load transient condition. The output
capacitor has no specific type or ESR requirement.
The amount of the capacitance may be increased
without limit. For PCB layout, the output capacitor
must be placed as close as possible to OUT and
GND pins, and keep the traces as short as
possible.
Enable/Shutdown Operation
The AP2280 is turned on by setting the EN pin high,
and is turned off by pulling it low. To ensure proper
operation, the signal source used to drive the EN
pin must be able to swing above and below the
specified turn-on/off voltage thresholds listed in the
Electrical Characteristics section under V
IL
and V
IH
.
Discharge Operation
The AP2280 offers discharge option that helps to
discharge the output when disabled. To use this
feature, the DIS pin is connected to OUT pin
externally. If this feature is not used, the DIS pin
should be left open.
Power Dissipation
The device power dissipation and proper sizing of
the thermal plane is critical to avoid thermal
shutdown and ensuring reliable operation. Power
dissipation of the device depends on input voltage
and load conditions and can be calculated by:
DSON
2
OUTD
xRIP = (1)
However, the maximum power dissipation that can
be handled by the device depends on the
maximum junction to ambient thermal resistance,
maximum ambient temperature, and maximum
device junction temperature, which can be
approximated by the equation below:
JA
A
AD
)TC125(
)T(max@P
θ
−°+
=
(2)
For example at V
IN
=5V, the typical R
DSON
= 80m.
For I
OUT
=2A, the maximum power dissipation
calculated using equation (1) is P
D
=0.32W. Based
on
JA
=160°C/W and equation (2), the calculated
junction temperature rise from ambient is
approximately 51°C. Since the maximum junction
temperature is 125°C, the operating ambient
temperature must be kept below 74°C to safely
operate the device.
On the other hand, at T
A
=85°C and V
IN
=5V, the
calculated maximum power dissipation from
equation (2) is P
Dmax
=0.25W. Hence the safe
operating maximum continuous current is 1.77A.
For other application conditions, the users should
recalculate the device maximum power dissipation
based on the operating conditions.
Application Note
