PM6641 datasheet(30/47 Pages) STMICROELECTRONICS

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Device description

PM6641

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7.9

Phase management

When all the three switching regulators high side MOSFETs are turned on simultaneously

the input root mean square (RMS) current could rise up to very high values, increasing the

system losses and inducing external components overheating. It’s possible to reduce the

input overall RMS current by inserting one ceramic capacitor as close as possible to each

switching regulator power supply input, reducing the impulsive input current path. However

this synchronous mode of operation is jitter-free and noise immune.

Another possible way to reduce the input RMS current is based on the phase shifting

technique, which decreases the total input current by delaying the regulators turn on pulse.

With three regulators turned on, the 120d eg phase shifting allows to reduce the overall

input current up to 1.73 times as depicted in the following configuration, in which three

independent regulators with Vout/Vin lower than 0.333 and identical output current (I) are

managed with synchronous or 120 deg phase shifted turning on.

Figure 32. SW regulator phase management

Each regulator RMS input current is easily computed:

Equation 7

defining TSW the switching period, equal to

and TON the high side MOSFET on

time.

IL1

IL2

IL3

IL1

IL2

IL3

ICIN

Synchronous

120deg delay

∫

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