PM6685 datasheet(45/52 Pages) STMICROELECTRONICS

Part #	PM6685

Description	Dual step-down main supply controller with auxilary voltages for notebook system power

PDF	52 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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45 / 52 page

PM6685

Design example

45/52

Design example

The following design example considers an input voltage from 7V to 16V. The two switching

outputs must deliver a maximum current of 5A. The selected switching frequencies are

200kHz for the 5V section and 300kHz for the 3.3V section.

10.1

Inductor selection

OUT5: ILOAD= 5A, 60% ripple current.

Equation 34

We choose standard value L = 6 uH

∆I

L(max) = 2.86A @VIN =16V

ILRMS = 5.07A

Ipeak = 5A + 0.95A = 6.43A

OUT3: ILOAD = 5A, 50% ripple current.

Equation 35

We choose standard value L=4 uH.

∆I

L(max) = 2.2A @VIN =16V

ILRMS = 5.04A

Ipeak = 5A + 1.1A = 6.1A

10.2

Output capacitor selection

We would like to have an output ripple greater than 35mV.

OUT5: POSCAP 6TPB330M

OUT3: POSCAP 6TPB330M

KHz

200

)

(

≈

⋅

−

⋅

KHz

300

)

(

≈

⋅

−

⋅

PM6685 Datasheet(PDF) 45 Page - STMicroelectronics

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