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5
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 LMZ35003 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
waveform becomes rectangular, as shown in
it is recommended that a load of 1 A or greater be applied to ensure that an accurate reading is obtained.
The LMZ35003 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.
Scope Measurements: Vin = 12 V, Vout = 5 V, Iout = 300 mA
Ch.3> PH Node
Figure 2. PH Node at 300-mA Load
SNVU294 – JULY 2013
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Figure
2. This is normal behavior. At heavier loads, the PH
Figure
3. When attempting to measure switching frequency,
Scope Measurements: Vin = 12 V, Vout = 5 V, Iout = 1.0 A
Ch.3> PH Node
LMZ35003EVM-001 Simple Switcher® Power Module Evaluation Module
Copyright © 2013, Texas Instruments Incorporated
Figure 3. PH Node at 1-A Load
Operation Notes
5
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