MP1530 – TRIPLE OUTPUT STEP-UP PLUS LINEAR REGULATORS FOR TFT BIAS

MP1530 Rev. 1.4

www.MonolithicPower.com

11

5/19/2006

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Selecting the Rectifier Diodes

The

MP1530’s

high

switching

frequency

demands high-speed rectifiers. Schottky diodes

are

recommended

for

most

applications

because of their fast recovery time and low

forward voltage. Typically, a 1A Schottky diode

is recommended for the step-up converter.

100mA Schottky diodes such as Central

Semiconductor CMPSH-3 are recommended

for low current charge-pump circuits.

Selecting the Output Capacitor of the

Step-Up Converter

The output capacitor is required to maintain the

DC output voltage. Low ESR capacitors are

preferred to keep the output voltage ripple to a

minimum. The characteristics of the output

capacitor also affect the stability of the

regulation control system. A 10µF ceramic

capacitor works well in most applications. In the

case of ceramic capacitors, the impedance of

the capacitor at the switching frequency is

dominated by the capacitance, and so the

output voltage ripple is mostly independent of

the ESR. The output voltage ripple is estimated

to be:

SW

LOAD

MAIN

IN

RIPPLE

f

2

C

I

V

V

1

V

×

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

≅

is the load current, and C2 is the capacitance of

the output capacitor of the step-up converter.

Selecting the Number of Charge-Pump

Stages

For highest efficiency, always choose the

lowest number of charge-pump stages that

meets the output requirement.

The number of positive charge-pump stages

D

MAIN

MAIN

DROPOUT

GH

POS

V

2

V

V

V

V

N

−

−

−

=

dropout margin for the linear regulator.

The number of negative charge-pump stages

D

MAIN

DROPOUT

GL

NEG

V

2

V

V

V

N

−

+

−

=

Selecting the Flying Capacitor in Charge-

Pump Stages

increases the output current capability. A 0.1µF

ceramic capacitor works well in most low

current applications. The flying capacitor’s

voltage rating must exceed the following:

MAIN

CX

V

N

V

×

>

Where N is the stage number in which the flying

capacitor appears.

Step-Up Converter Compensation

The MP1530 uses current mode control which

unlike voltage mode has only a single pole roll

equated from the product of current control to

1

FB

EA

CSCONTROL

DC

A

Av

A

Av

×

×

=

LOAD

IN

CSCONTROL

I

V

4

A

×

=

MAIN

1

FB

1

FB

V

V

A

=

MAIN

LOAD

1

FB

IN

DC

V

I

V

V

1600

Av

×

×

×

=

The output filter pole is given in hertz by:

2

C

V

I

f

MAIN

LOAD

FILTERPOLE

×

×

π

=

The output filter zero is given in hertz by:

2

C

R

2

1

f

ESR

FILTERZERO

×

×

π

=

series resistance.