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MP1530DQ-LF-Z

Triple Output Step-Up Plus Linear Regulators for TFT Bias

Monolithic Power Systems 

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

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:

VRIPPLE

≅ ⎜⎜⎝⎛1 −

VIN

VMAIN

⎟⎟⎠⎞

×

ILOAD

C2 × fSW

Where VRIPPLE is the output ripple voltage, ILOAD

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

NPOS is given by:

NPOS

=

VGH

− VDROPOUT − VMAIN

VMAIN − 2VD

Where VD is the forward voltage drop of the

charge-pump diode, and VDROPOUT is the

dropout margin for the linear regulator.

The number of negative charge-pump stages

NNEG is given by:

NNEG

=

−VGL + VDROPOUT

VMAIN − 2VD

Use VDROPOUT = 1V for positive charge-pump

and VDROPOUT = 0.3V for negative charge-pump.

Selecting the Flying Capacitor in Charge-

Pump Stages

Increasing the flying capacitor CX values

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:

VCX > N × VMAIN

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

off due to the output filter. The DC gain (AVDC) is

equated from the product of current control to

output gain (AVCSCONTROL), error amplifier gain

(AVEA), and the feedback divider.

Av DC = A CSCONTROL × Av EA × A FB1

A CSCONTROL

= 4 × VIN

ILOAD

A FB1

=

VFB1

VMAIN

Av DC

=

1600 × VIN × VFB1

ILOAD × VMAIN

The output filter pole is given in hertz by:

fFILTERPOLE

=

ILOAD

π × VMAIN × C2

The output filter zero is given in hertz by:

fFILTERZERO

=

1

2π × RESR

× C2

Where RESR is the output capacitor’s equivalent

series resistance.

MP1530 Rev. 1.4

www.MonolithicPower.com

11

5/19/2006

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© 2006 MPS. All Rights Reserved.

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