DPA424 Power Integrations, Inc., DPA424 Datasheet - Page 16

• Manufacturer Part Number: DPA424
• Description: Highly Integrated DC-DC Converter Ics For Distributed Power Architectures
• Manufacturer: Power Integrations, Inc.

the energy in inductor L2 while Q1 is still off. The transformer
reset voltage on the secondary winding directly drives a positive
voltage on the gate of catch MOSFET, Q1. MOSFET Q1
provides a low loss conduction path for a substantial portion of
the primary off-time.
An isolated auxiliary winding on L2, rectified and filtered by
D1 and C4, provides the bias supply for the optocoupler
transistor.
Output regulation is achieved by using secondary side voltage
reference, U3. The resistor divider formed by R10 and R11,
together with the reference voltage, determines the output
voltage. Diode D3 and C13 form a soft-finish network that,
together with the internal duty cycle and current limit soft-start
of the DPA-Switch, prevent output overshoot at start-up. Resistor
R7 ensures that the soft-finish capacitor is discharged quickly
when the output falls out of regulation.
Control loop response is shaped by R6, C16, R12, C14, R9, R4
and C5, providing a wide bandwidth and good phase margin at
gain crossover. Since the PWM control in DPA-Switch is
voltage mode, no slope compensation is required for duty
cycles above 50%.
Key Application Considerations
DPA-Switch Design Considerations
Power Table
This section explains how to use the power tables 1, 3 and 4.
These provide two types of information. The first is the expected
device dissipation for a given output power. The second is the
maximum practical output power possible when operating at
internal minimum current limit. Each table specifies the input
voltage range and assumes a single 5 V output using Schottky
diode rectification.
For example, referring to Table 1, a DPA424R would typically
dissipate 1 W in a 23 W converter and has a maximum power
capacity of 40 W. In the same converter the DPA425R would
dissipate 0.5 W. Selecting the DPA425R with reduced dissipation
would increase overall converter efficiency by approximately
2%.
The dissipation data assumes adequate heat sinking to keep the
junction temperature at or below 100 °C, maximum data sheet
R
representing 6% of the total output power, and combined loss
in magnetic components representing 6% of the total output
power. DPA-Switch losses are based on a ratio between
conduction and switching losses of approximately 3:1. These
assumptions are typical for a single 5 V output forward converter
design using Schottky rectification and adequately designed
magnetic components.
16
DS(ON)
DPA423-426
figure at a junction temperature of 100 °C, a diode loss
J
5/03
Table 3. Output Power Table for 16 VDC Minimum Input Voltage.
Notes: 1. Maximum output power is limited by device internal
current limit. This is either peak output power or continuous power if
adequate heat sinking is provided to keep T
assume worst case R
forward converter configuration with diode rectification. Up to 5% higher
output power possible using synchronous rectification. 4. See Part
Ordering Information.
Table 4. Output Power Table for 24 VDC Minimum Input Voltage
Issues Affecting Dissipation:
1) Using synchronous rectification will tend to reduce device
2) Designs with lower output voltages and higher currents will
3) Reduced input voltage decreases the available output power
DPA-Switch Selection
Use tables 1, 3 and 4 to select the DPA-Switch based on device
dissipation. Selecting the optimum DPA-Switch depends upon
required maximum output power, efficiency, heat sinking
constraints and cost goals. With the option to externally reduce
Total Device
PRODUCT
Total Device
PRODUCT
Dissipation 0.5 W 1 W
DPA423R
DPA424R
DPA425R
DPA426R
Dissipation 0.5 W 1 W
DPA423R
DPA424R
DPA425R
DPA426R
dissipation.
tend to increase the device dissipation listed in the power
table.
for the same device dissipation. Tables 3 and 4 are the power
tables for 16 VDC and 24 VDC input voltages. Input
voltages below 16 V are possible, but since the internal start-
up current source is not specified at voltages below 16 V, an
external chip supply current should be fed into the CONTROL
pin approximately equal to but less than I
(See Table 3 for Notes).
4
OUTPUT POWER TABLE
4
OUTPUT POWER TABLE
10 W 14 W 22 W 27 W
12 W 16.5 W 25 W 31 W 37 W 43 W
5 W
7 W 10 W 15 W
11 W 16 W 23.5 W
16 W 22 W 35 W 43 W
18 W 25 W 39 W 48 W 58 W 65 W
8 W 11 W
DS(ON)
16-32 VDC RANGE
24-48 VDC RANGE
7 W
@ T
J
= 100 °C. 3. All powers based on
2.5 W 4 W
2.5 W
-
-
J
2,3
< 125 °C. 2. All powers
2,3
4 W
-
-
-
-
CD1
6 W
.
6 W
-
-
-
-
Output
15.5 W
7.5 W
11.5 W
Power
Output
31 W
Power
25 W
47 W
Max
Max
1
1