MP3430 — 90V STEP-UP CONVERTER WITH APD CURRENT MONITOR

MP3430 Rev 1.11

www.MonolithicPower.com

12

4/25/2013

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The peak inductor current must always be

less than the MP3430 current limit and the

inductor saturation current.

In addition, chose an inductor such that the

saturation current is greater than either the IC

current limit (900mA, typ.) or the worst-case

calculated peak current—whichever is smaller.

Generally, pick an inductor with at least 20%

greater saturation current than the IC current limit,

so that the minimum saturation current would be

1.08A (900mA + 180mA). To ensure that the

calculated maximum current does not exceed the

maximum current allowed by the MP3430.

IN

1

L,PEAK

S

VD

I900mA

Lf







, typical

Diode Design

Due to the high-output voltage combined with the

diode capacitive coupling, there is a significant

reverse current through the inductor. Generally, a

low reverse bias capacitance equates to a low

reverse inductor current. However, this is not

always true though; so test the diodes prior to

final selection. Two recommended diodes with

relatively

small

reverse

currents

are

the

DFLS1150-7 (Diodes Inc, Schottky, 1A (avg),

150V) and the BAT46ZFILM (STMicroelectronics,

Schottky, 150mA (avg), 100V)

Also, select a diode with an RMS current rating

greater than the actual RMS current. The

minimal (2.7V). The RMS current equation is:

2

DIODE, RMS

RMS

PK

D

II

I

3





1IN

2

OUT

IN

DV

D

VV







current is 2.5mA (typ). For faster response,

chose the maximum output less than the

maximum allowed voltage.

APD, MAX

MON1, MAX

I

I

10



APD, MAX

MON2, MAX

I

I

2



MON1, MAX

MON1

MON1, MAX

V

R

I



MON2, MAX

MON2

MON2, MAX

V

R

I



Where:

The output ripple is typically 0.1%. Use 0.1µF

capacitor for most cases. Make sure that the

capacitor voltage rating is at least 50% more than

APD

2

OUT,RIPPLE

SOUT

I(1 D )

V0.001

fC







power start-up. This may cause false starts.