Texas Instruments UCC29950EVM-631, User Manual, Page: 14 / 38

Test Setup
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5.4 Power-Up/Power-Down Procedure: Aux Bias Mode
The following test procedure is recommended primarily for power up and shutting down the evaluation
module in Aux Bias Mode. Never leave a powered EVM unattended for any length of time. Also, the unit
should never be handled while power is applied to it. The UCC29950EVM-631 is set at the factory to
operate in Aux Bias Mode, with an external bias supply as shown in
Figure 4 . Operation in Self Bias
Mode, without an external bias supply is described in Section 5.3 .
WARNING
There are very high voltages present on the EVM. Some
components reach temperatures above 50°C. Precautions must be
taken when handling the board. Never operate the UCC29950EVM-
631 without the fan running. Always make certain the bulk
capacitor (C6) has completely discharged prior to handling the
EVM.
1. Working at an ESD workstation, make sure that the ionizer is on before the EVM is removed from the
protective packaging. Electrostatic smock and safety glasses should also be worn. Because voltages in
excess of 400 V may be present on the EVM, do not connect the ground strap from the smock to the
bench. If testing with a load, set the electronic load to Constant Current Mode.
2. Power Up in Aux Bias Mode:
(a) Connect the equipment as shown in Figure 4 .
(b) Set the electronic load to 2 A.
(c) Set the two switches, S1 and S2 to the 'off' position, switch toggle pointed to the heatsink as shown
in Figure 6 .
(d) Check that the link connects pin 1 to pin 2 of J4.
(e) Turn on the 13-V bias supply.
(f) Set S2 to the 'on' position. switch toggle pointed away from the heatsink as shown in Figure 7 .
(g) Turn on the fan.
(h) Set the AC source voltage between 90 V
AC
and 264 V
AC
.
(i) Turn the AC source on.
(j) Verify that the output of the module is within regulation.
NOTE: The Power Up procedure given above will always work. However, providing that the bias
supply has not been interrupted and S2 is in the 'on' position, the EVM will power up and
down as the AC source is turned on and off.
5.5 Equipment Shutdown
1. To quickly discharge the output capacitors, make sure there is a load greater than 0 A on the EVM.
2. Turn off the AC source.
3. Turn off the bias source if operating in Aux Bias Mode.
4. Using the voltmeter at V2, check that the voltage on the bulk capacitor, C6, has fallen to a safe level.
14 Using the UCC29950EVM-631 300-W PFC/LLC Off-Line PSU Module SLUUB69A – March 2015 – Revised March 2015
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