EUP3420
Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
PC Board Layout Checklist
For all switching power supplies, the layout is an
important step in the design especially at high peak
currents and switching frequencies. If the layout is not
carefully done, the regulator might show stability
problems as well as EMI problems.
When laying out the printed circuit board, the following
guidelines should be used to ensure proper operation of
the EUP3420.
1. The input capacitor C
IN
should connect to VIN as
closely as possible. This capacitor provides the AC
current to the internal power MOSFETs.
2. The power traces, consisting of the GND trace, the
SW trace and the VIN trace should be kept short,
direct and wide.
3. The FB pin should connect directly to the feedback
resistors. The resistive divider R1/R2 must be
connected between the C
OUT
and ground.
4. Keep the switching node, SW, away from the
sensitive FB node.
R2
VOUT
=
0.5V
1
+
R1
Choose R1 value 50kΩ for most applications.
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown below.
Thermal Considerations
To avoid the EUP3420 from exceeding the maximum
junction temperature, the user will need to do a thermal
analysis. The goal of the thermal analysis is to determine
whether the operating conditions exceed the maximum
junction temperature of the part. The temperature rise is
given by:
T
R
=(P
D
)(θ
JA
)
Where P
D
=I
LOAD2
× R
DS(ON)
is the power dissipated by
the regulator ;
θ
JA
is the thermal resistance from the
junction of the die to the ambient temperature.
The junction temperature, T
J
, is given by:
T
J
=T
A
+T
R
Where T
A
is the ambient temperature.
T
J
should be below the maximum junction temperature
of 125°C.
DS3420
Ver1.2
Mar. 2009
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
