PM6644 datasheet(23/35 Pages) STMICROELECTRONICS

23 / 35 page

PM6644

Application information

Doc ID 023203 Rev 1

23/35

K is a constant (< 0.1) that defines the ratio between the controller bandwidth and the

switching frequency.

The output capacitor must store the inductor energy generating an output ripple within the

output voltage ripple requirements.

If an output tantalum capacitor is used, in CCM the voltage ripple VRIPPLEout is given by:

Equation 14

A low ESR capacitor is required to reduce the output voltage ripple.

If an output ceramic capacitor is used, in CCM the voltage ripple VRIPPLEout is given by:

Equation 15

Finally the output capacitor choice heavily impacts the load transient response.

Table 12 shows a list of some capacitor part numbers.

3.1.4

Maximum RMS output current

Both high-side and low-side embedded power MOSFETs of the switching regulator can

withstand a maximum RMS current of 300 mA.

The maximum sustainable RMS output current ILOADRMS of the switching regulator depends

on the application specifications of:

●

input voltage VIN

●

output voltage VOUT

●

inductor current ripple

∆IL (that depends on the switching frequency FSW and on the

inductor value L, according to Equation 7 ).

The maximum RMS currents of high-side (IRMS,HS) and low-side (IRMS,LS) MOSFETs are

given by:

Equation 16

Table 12.

Output capacitor part number

Manufacturer

Part number

Capacitor value

(

µF)

Rated voltage (V)

ESR max. (M

Ω)

TAYIO YUDEN

JMK212BJ226MG-T

6.3

SANYO

POSCAP 6TPC33M

6.3

7 to 15

RIPPLEout

out

∆I

⋅

RIPPLEout

∆I

⋅

OUT

⋅

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

RMS HS

LRMS

LOAD

()

∆I

()

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

⋅

300mA

⋅

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