LYT0002/0004-0006
U1
+
D
S
S
S
S
C2
R1
FB
BP
RV1
L1
DC
OUTPUT
AC
INPUT
D1
VR1
C5
C1
C3
~
+
–
L2
~
RF1
BR1
Optimize hatched copper areas (
) for heat sinking.
PI-7032-061313
Figure 7b. Recommended Printed Circuit Layout for LYTSwitch-0 in a Buck Converter Configuration using D Package to Bottom Side of the Board.
switching nodes, the LYTSwitch-0 should be placed away from
AC input lines. It may be advantageous to place capacitors C1
and C2 in-between LYTSwitch-0 and the AC input.
RDS(ON) from part to part. A battery powered thermocouple
meter is recommended to make measurements when the
SOURCE pins are a switching node. Alternatively, the
ambient temperature may be raised to indicate margin to
thermal shutdown.
Quick Design Checklist
4. Check for any presence of reverse current in the DRIAN pin
during start-up with the output capacitance fully discharged.
Presence of reverse current is possible for CCM (high-power
inductance >3 mH) at certain conditions for limited input
capacitance (VOUT = VBULK_MIN every input half-line AC cycle).
Using a current probe, check if negative current is measured
either by increase input capacitance, reduce inductance or
place an ultrafast diode in series with the Drain node.
5. Follow the design procedure in AN-60 for the optimum line
regulation.
As with any power supply design, all LYTSwitch-0 designs
should be verified for proper functionality on the bench. The
following minimum tests are recommended:
1. Correct diode selection – UF400x series diodes are
recommended only for designs that operate in MDCM at an
ambient of 70 °C or below. For designs operating in
continuous conduction mode (CCM) and/or higher ambient,
then a diode with a reverse recovery time of 35 ns or better,
such as the BYV26C, is recommended.
2. Maximum drain current – Verify that the peak drain current is
below the data sheet peak drain specification under
worst-case conditions of highest line voltage, maximum
overload (just prior to auto-restart) and highest ambient
temperature.
3. Thermal check – At maximum output power, minimum input
voltage and maximum ambient temperature, verify that the
LYTSwitch-0 SOURCE pin temperature is 110 °C or below.
This figure ensures adequate margin due to variations in
6. Power factor can be optimized by adjusting the conduction
time of the bridge rectifier. Refer to AN-60 for more details.
In a LYTSwitch-0 design using a buck or buck-boost converter
topology, the SOURCE pin is a switching node. Oscilloscope
measurements should therefore be made with probe grounded
to a DC voltage, such as primary return or DC input rail, and not
to the SOURCE pins. The power supply input must always be
supplied from an isolated source (e.g. via an isolation transformer).
8
Rev. A 06/13
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