MP3430 datasheet(13/15 Pages) MPS

13 / 15 page

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

MP3430 Rev 1.11

www.MonolithicPower.com

4/25/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

Recommended Values (VIN: 2.7V to 5.5V)

VOUT

(V)

IOUT,MAX

(mA)

(µH)

RFB,TOP

(MΩ)

(VOUT to FB)

RFB,BOTTOM

(kΩ)

(FB to GND)

Diode

(Schottky

Small Signal)

COUT

(µF

100V)

CIN

(µF)

2.5

3.3

27.4

2.5

2.7

20.5

2.5

2.0

16.2

2.0

1.5

13.3

0.9

1.5

11.5

0.5

1.2

10.0

0.5

1.0

8.87

BAT46W

0.1

Design Example:

Desired Parameters:

VIN = 2.7V to 5.5V

IAPD,MAX = 2.5mA

VIN,TYP = 3.3V

VMON1,MAX = 0.5V

VOUT = 50V

VMON2,MAX = 0.5V

VFB = 0.8V

RTOP = 1MΩ

fS = 1.3MHz;

tS = 769ns

Calculations:

VOUT



















OUT

TOP

BOTTOM

R_RLIM = 68 / IAPD,MAX = 68/2.5-= 27.2kΩ

Inductor

Choose L = 2.0µH

First Consideration (most important)

MAX,REVERSE

OUT

40pF /L 50

40pF / 2 H 224mA







 

MAX,REVERSE

Re verseCurrent

IN,MIN

1.6 L I

1.6 2 H 224mA

194ns

2.7 1



 







SOUT

OUT

2L f

22 1.3 2.5

0.00026

1000

50 1000

 











OUT

IN,MIN

0.00026

2 50

D2.2

2.2

2.7

0.639



































OUT

IN,MIN

2.7

0.639

0.0365

50 2.7









1 D

1 0.639 0.0365 0.325





 





Re verseCurrent

250ns t

194ns







So 2.0µH is good.

Second Consideration

IN,MIN

CRIT

OUT

CRIT,MIN

OUT

SOUT

KD D'

2.7

0.00276

1000

0.00276 50 1000

L21 H

2 1.3 2.5

 











 



 



 









 



 







 





KCRIT>K : 0.00276>0.00026.

Third Consideration:

IN,MIN

L,PEAK

2.7 0.639

I664mA 900mA

L f

2.0 1.3











Make sure the inductor has at least 20% more

capability than the saturation current

DIODE

D2 = diode conduction fraction of period = 0.0365

DIODE,RMS

RMS

0.0365

664

73mA









Make sure diode average current rating is above

this value

Output Capacitor

Choose COUT = 0.1µF

APD

OUT,RIPPLE

SOUT

I(1 D )

V0.001

2.5 (1 0.0365)

0.001 19mV

1.3 0.1















= 0.04% of VOUT ,<0.1%

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