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MP1531

Low Power, Triple Output Step-Up Plus Charge Pump for TFT Bias

Monolithic Power Systems 

MP1531 – LOW POWER, TRIPLE OUTPUT STEP-UP PLUS CHARGE PUMP FOR TFT BIAS

Selecting the Inductor

The inductor is required to force the higher

output voltage while being driven by the input

voltage. A larger value inductor results in less

ripple current that results in lower peak inductor

current. However, the larger value inductor has

a larger physical size, higher series resistance,

lower saturation current for a given package

size.

Choose an inductor that does not saturate at

heavy load transients and start-up conditions. A

good rule for determining the inductance is to

allow the peak-to-peak ripple current to be

approximately 30-50% of the maximum input

current. Make sure that the peak inductor

current is below the device current limit to

prevent loss of regulation. Calculate the

required inductance value by the equation:

( ) L1 = VIN VMAIN − VIN

VMAIN × fSW × ∆I

Where VIN is the input voltage, fSW is the

switching frequency, and ∆I is the peak-to-peak

inductor ripple current.

Selecting the Input Capacitor

An input capacitor is required to supply the AC

ripple current to the inductor, while limiting noise

at the input source. A low ESR capacitor is

required to keep the noise at the IC to a minimum.

Since it absorbs the input switching current it

requires an adequate ripple current rating. Use a

capacitor with RMS current rating greater than the

inductor ripple current (see Selecting The Inductor

to determine the inductor ripple current). The

input capacitor in Figure 3 is necessary in most

lab setups, but can be reduced in typical

application circuits if the source impedance is

lower.

VIN

2.7V to 4.2V

OFF ON

RDY

SW

D7

BAS40-04-7

VGL

-10V

C4

10nF

CT

EN

RDY

COMP

IN

SW

FB1

D6

BAS40-04-7

D5

BAS40-04-7

C3

10nF

IN2

MP1531

IN3

GL

C9

56pF

FB2

GH

REF

GND

FB3

PGND

D1

B0530W

VMAIN

5V

D2

BAS40-04-7

D4

BAS40-04-7

D3

BAS40-04-7

C7

56pF

VGH

15V

Figure 3—Triple Output Boost Application Circuit

MP1531 Rev. 1.2

www.MonolithicPower.com

8

5/22/2006

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