LP5550 datasheet(21/28 Pages) TI1

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IRMS_CIN = IOUT

VOUT x (VIN - VOUT)

VIN

(A)

ICL_AVG = ICL_PK - ' iL

= ICL_PK -

D x (VIN - VOUT)

2 x L x fS

0.4 -

D x (VIN - VOUT)

fS = 1 MHz,

L = 10 PH

0.4 -

D x (VIN - VOUT)

9.4

fS = 1 MHz,

L = 4.7 PH

IL(MAX) = ILOAD(MAX) + ' iL(MAX)

= ILOAD(MAX) +

D x (VIN(MAX) - VOUT)

2 x L x fS

= ILOAD(MAX) +

D x (VIN(MAX) - VOUT)

9.4

(A)

fS = 1 MHz,

L = 10 PH

fS = 1 MHz,

L = 4.7 PH

PWI

Voltages

Shutdown Command

OFF

Off

EN and

RESETN

LP5550

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SNVS378G – OCTOBER 2005 – REVISED APRIL 2013

Figure 29. ENABLE and RESETN Operation

INDUCTOR

A 10uH or 4.7uH inductor should be used with the LP5550. The inductor should be rated to handle the peak load

current plus the ripple current:

(3)

CURRENT LIMIT

The switching converter in the LP5550 detects the peak inductor current and limits it for protection (see Electrical

Characteristics table and/or Typical Performance Characteristics section). To determine the average current limit

from the peak current limit, the inductor size, input and output voltage, and switching frequency must be known.

The LP5550 is designed to work with a 4.7uH or 10uH inductor, so:

(4)

INPUT CAPACITOR

The input capacitor to the switching converter supplies the AC switching current drawn from the switching action

of the internal power FETs. The input current of a buck converter is discontinuous, so the ripple current supplied

by the input capacitor is large. The input capacitor must be rated to handle this current:

(5)

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