PM6644 datasheet(24/35 Pages) STMICROELECTRONICS

24 / 35 page

Application information

PM6644

24/35

Doc ID 023203 Rev 1

Equation 17

where ILOAD is the RMS output current.

The minimum ILOAD between equation 16 and equation 17, combined with RMS load current

limitation due to valley current limit (Equation 6 ), determines the maximum RMS output

current ILOADRMS sustained by the switching regulator:

Equation 18

Example 1

VIN = 5 V, FB = VCC (VOUT = 3.47 V), ∆IL= 68.5 mA (L = 33 uH, Fsw = 470 kHz).

High-side can withstand a load current of ILOADRMS = 432 mA.

Low-side can withstand a load current of ILOADRMS = 977 mA.

ILOADRMS due to valley current limit = 384 mA.

As a result, ILOADRMS = 384 mA (limitation determined by the valley current limit).

The PM6644 switching regulator can source 384 mA RMS. 384 mA is also the peak load

current.

Example 2

VIN = 25 V, FB = VCC (VOUT = 3.47 V), ∆IL = 192.5 mA (L = 33 uH, Fsw = 470 kHz).

High-side can withstand a load current of ILOADRMS = 2164 mA.

Low-side can withstand a load current of ILOADRMS = 344 mA.

ILOADRMS due to valley current limit = 446 mA.

As a result, ILOADRMS = 344 mA (limitation determined by the low-side RMS max. current).

The PM6644 switching regulator can source 344 mA RMS. The peak load current is 446

mA.

RMS LS

LRMS

–

()

LOAD

()

∆I

()

----------------

⋅

300mA

LOADRMS

MIN

300mA

-------------------

⎝⎠

⎛⎞

∆I

()

-------------

–

300mA

–

-------------------

⎝⎠

⎛⎞

∆I

()

-------------

–

350mA

∆I

--------

⎩⎭

⎪⎪

⎨⎬

⎪⎪

⎧⎫

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