Datasheet

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5 Test Setup
5.1 Test Equipment
Voltage Source, VIN: The input voltage shall be a variable DC source capable of supplying between 0
V
DC
and 75 V
DC
at no less than 3.5 A
DC
, and connected to J1 and A1 as shown in Figure 2. For fault
protection to the unit, good common practice is to limit the source current to no more than 3.5 A
DC
for a
36-V input. A DC ammeter, A1 should also be inserted between VIN and J1 as shown in Figure 2. For
highest accuracy, such as gathering efficiency data, V
IN
should be measured directly across the input
capacitor.
External PVDD DC Power Supply (Optional): The design allows for separate VDD and PVDD, allowing
the gate drive voltage amplitude to be separately biased from the rest of the device. By removing R29, the
gate drive voltage for Q1 and Q2 can be derived from an external DC power supply applied to J11 and
J12. Be cautious not to exceed the maximum gate-to-source voltage rating (V
GS(max)
= 20 V) of Q1 and Q2.
Do not connect an external DC power supply to J11 and J12 when R29 is installed
Output Load, LOAD1: For the output load to V
OUT
, a programmable electronic load set to constant current
mode and capable of sinking 0 A
DC
to 30 A
DC
, shall be used. For convenience, V
OUT
can be monitored by
connecting a DC voltmeter, V2, to J9 and J10. For highest accuracy, such as gathering efficiency data,
V
OUT
should be measured directly across the output capacitor at J13.
Network Analyzer (Optional): A network analyzer can be connected directly to J6 and J7. The UCC2897
reference design provides a 51.1-Ω resistor (R25) between the output and the voltage feedback to allow
easy non-invasive measurement of the control to output loop response
Fan: Most power converters include components that can be hot to the touch when approaching
temperatures of 60°C. Because this design is not enclosed to allow probing of circuit nodes, a small fan
capable of 200 LFM to 400 LFM is recommended to reduce component temperatures when operating at
or above 50% maximum rated load current
Recommended Wire Gauge: The connection between the source voltage, V
IN
and J1 can carry as much
as 3.25 A
DC
. The minimum recommended wire size is AWG #20 with the total length of wire less than 8
feet (4 feet input, 4 feet return). The connection between J8 and LOAD1 can carry as much as 30 A
DC
.
The minimum recommended wire size is AWG #16, with the total length of wire less than 8 feet (4 feet
output, 4 feet return).
6
48-V to 3.3-V Forward Converter with Active Clamp Reset —Using the SLUU357–November 2009
UCC2897A Active Clamp Current Mode —PWM Controller
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