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2.7 Input Voltage Ripple

V = 2 V/div

(PH)

V = 7 V, V = 3.3 V, I = 5 A, f = 700 kHz

I O O S

V = 100 mV/div (ac) coupled

I(Ripple

)

2.8 Powering Up

V = 5 V/div

V = 2 V/div

Time - 5 ms/div

Test Setup and Results

The input voltage ripple is shown in Figure 7 . The input voltage is VIN = 12 V for the TPS54550. Output

current for each device is at full rate TPS54550EVM-158 load of 5 A.

Figure 7. Input Voltage Ripple, TPS54550

The TPS54550EVM-158 start-up waveforms are shown in Figure 8 . The top trace shows VIN whereas the

bottom trace shows OUT. Vin charges up from 0 V toward 12 V. When the input voltage reaches the

internally set UVLO threshold voltage, the slow-start sequence begins. After a delay, the internal reference

begins to ramp up linearly at the internally set slow-start rate towards 0.891 V, and the output ramps up

toward the set voltage of 5 V. The output may be inhibited by using a jumper at JP1 to tie EN to GND.

When the jumper is removed, EN is released and the slow-start voltage begins to ramp up at the internally

set rate. When the EN voltage reaches the enable-threshold voltage of 1.06 V, the start-up sequence

begins as described previously.

Figure 8. Power Up, OUT Relative to VIN

SLVU151 – March 2006 TPS54550EVM-158 SWIFT™ Regulator Evaluation Module 7

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