Scope Measurements: Vin = 12 V, Vout = 5 V, Iout = 1.0 A

Ch.3> PH Node

Scope Measurements: Vin = 12 V, Vout = 5 V, Iout = 300 mA

Ch.3> PH Node

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Operation Notes

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Operation Notes

The UVLO threshold of the factory-stock EVM is approximately 6.5 V with a 0.5-V hysteresis. The input

voltage must be above the UVLO threshold before power conversion will begin. The UVLO threshold is set

by resistors R10 and R11. See the data sheet for information on setting the UVLO voltage.

Once the input voltage rises above the UVLO threshold, power conversion begins and the output voltage

ramps to its final value in approximately 10 ms. If desired, this soft-start interval can be increased by

adding capacitance at location C4 on the bottom side of the EVM. This location is not populated on the

factory-stock EVM.

The TPS84250 is a nonsynchronous buck regulator. This means that the power stage can only source

current and does not sink current. This also means at lighter loads, the waveform observed on the PH test

node exhibits considerable ringing as shown in Figure 2. This is normal behavior. At heavier loads, the PH

waveform becomes rectangular, as shown in Figure 3. When attempting to measure switching frequency,

it is recommended that a load of 1 A or greater be applied to ensure that an accurate reading is obtained.

The TPS84250 is not designed to endure a sustained short circuit on its output. It can survive momentary

shorts (< 5 seconds), but sustained short circuits may cause permanent damage to the device.

Figure 2. PH Node at 300-mA Load

Figure 3. PH Node at 1-A Load

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SLVU460A – November 2011 – Revised July 2012

TPS84250EVM-001 2.5-A, Integrated Power Solution Evaluation Module

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