DPA423 Power Integrations, Inc., DPA423 Datasheet - Page 19

• Manufacturer Part Number: DPA423
• Description: Highly Integrated DC-DC Converter Ics For Distributed Power Architecturesthe Dpa-switch ic Family Introduces a Highly Integratedsolution For DC-DC Conversion Applications in The 16-75 Vdcinput Range.dpa-switch Uses The Same Proven Topology as Topswit
• Manufacturer: Power Integrations, Inc.

Primary Side Connections
The tab of DPA-Switch R package is the intended return path for
the high switching currents. Therefore, the tab should be
connected by wide, low impedance traces back to the input
decoupling capacitor. The SOURCE pin should not be used to
return the power currents; incorrect operation of the device may
result. The SOURCE is only intended as a signal ground. The
device tab (SOURCE) is the correct connection for power
currents with the R package.
The CONTROL pin bypass capacitor should be located as
close as possible to the SOURCE and CONTROL pins and its
SOURCE connection trace should not be shared by the main
MOSFET switching currents. All SOURCE pin referenced
components connected to the LINE-SENSE or EXTERNAL
CURRENT LIMIT pins should also be located closely between
their respective pin and SOURCE. Once again, the SOURCE
connection trace of these components should not be shared by
the main MOSFET switching currents. It is critical that
the tab (SOURCE) power switching currents are returned to the
input capacitor through a separate trace that is not
shared by the components connected to CONTROL,
LINE-SENSE or EXTERNAL CURRENT LIMIT pins.
Any traces to the L or X pins should be kept as short as possible
and away from the DRAIN trace to prevent noise coupling.
LINE-SENSE resistor (R1 in Figure 25) should be located close
to the L pin to minimize the trace length on the L pin side.
In addition to the CONTROL pin capacitor (C6 in Figure 25),
a high frequency bypass capacitor in parallel is recommended
as close as possible between SOURCE and CONTROL pins for
better noise immunity. The feedback optocoupler output should
also be located close to the CONTROL and SOURCE pins of
DPA-Switch.
Heat Sinking
To maximize heat sinking of the DPA-Switch R or G package
and the other power components, special thermally conductive
PC board material (aluminum clad PC board) is recommended.
This has an aluminum sheet bonded to the PC board during the
manufacturing process to provide heat sinking directly and
allow the attachment of an external heat sink. If normal PC
board material is used (such as FR4), providing copper areas on
both sides of the board and using thicker copper will improve
heat sinking.
If an aluminum clad board is used then shielding of switching
nodes is recommended. This consists of an area of copper
placed directly underneath switching nodes such as the drain
node, and output diode to provide an electrostatic shield to
prevent coupling to the aluminum substrate. These areas are
connected to input negative in the case of the primary and output
return for secondary. This reduces the amount of capacitive
coupling into the insulated aluminum substrate that can then
appear on the output as ripple and high frequency noise.
Quick Design Checklist
As with any power supply design, all DPA-Switch designs
should be verified on the bench to make sure that component
specifications limits are not exceeded under worst case
conditions. The following minimum set of tests for DPA-Switch
forward converters is strongly recommended:
1. Maximum drain voltage – Verify that peak V
2. Transformer reset margin – Drain voltage should also be
3. Maximum drain current – At maximum ambient temperature,
4. Thermal check – At maximum output power, minimum
Design Tools
Up-to-date information on design tools is available at the Power
Integrations Web site: www.powerint.com.
exceed minimum BV
maximum overload output power. It is normal, however, to
have additional margin of approximately 25 V below BV
to allow for other power supply component unit-to-unit
variations. Maximum overload output power occurs when
the output is loaded to a level just before the power supply
goes into auto-restart (loss of regulation).
checked at highest input voltage with a severe load step (50-
100%) to verify adequate transformer reset margin. This test
shows the duty cycle at high input voltage, placing the most
demand on the transformer reset circuit.
maximum input voltage and maximum output load, verify
drain current waveforms at start-up for any signs of
transformer or output inductor saturation and excessive
leading edge current spikes. DPA-Switch has a leading edge
blanking time of 100 ns to prevent premature termination of
the on cycle. Verify that the leading edge current spike does
not extend beyond the blanking period.
input voltage and maximum ambient temperature, verify
that temperature specifications are not exceeded for the
transformer, output diodes, output choke(s) and output
capacitors. The DPA-Switch is fully protected against over-
temperature conditions by its thermal shutdown feature. It is
recommended that sufficient heat sinking is provided to
keep the tab temperature at or below 115 °C (R package),
SOURCE pins at or below 100 °C (P/G packages) under
worst case continuous load conditions (at low input voltage,
maximum ambient and full load). This provides adequate
margin to minimum thermal shutdown temperature
(130 °C) to account for part-to-part R
monitoring device temperatures, note that the junction-to-
case thermal resistance should be accounted for when
estimating die temperature.
DSS
at highest input voltage and
DPA423-426
DS(ON)
variation. When
DS
4/04
does not
L
19
DSS