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0.7

4.0

3.5

0.8

0.9

1.0

1.1

1.2

5.0

4.5

6.0

5.5

325 kHz

325 kHz

350 kHz

375 kHz

400 kHz

350 kHz

375 kHz

400 kHz

UDG−06072

PTH04T220W, PTH04T221W

SLTS275A – DECEMBER 2006 – REVISED FEBRUARY 2007

The maximum input voltage allowed for proper synchronization is duty cycle limited. When using Smart Sync,

the maximum allowable input voltage varies as a function of output voltage and switching frequency.

Operationally, the maximum input voltage is inversely proportional to switching frequency. Synchronizing to a

higher frequency causes restrictions on the input voltage range. For a given switching frequency, Figure 26

shows how the maximum input voltage varies with output voltage.

For example, for a module operating at 400 kHz and an output voltage of 0.8 V, the maximum input voltage is

5.3 V. Exceeding the maximum input voltage may cause in an increase in output ripple voltage and increased

output voltage variation.

As shown in Figure 26, the input voltage and output voltage limits apply when synchronizing to frequencies

greater than the free-running frequency. See the Electrical Characteristics table for the synchronization

frequency range limits.

Maximum Input Voltage

vs

Minimum Output Voltage

Figure 26.

26

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