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MP1530

Triple Output Step-Up Plus Linear Regulators for TFT Bias

MPS Industries, Inc. 

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

APPLICATION INFORMATION

COMPONENT SELECTION

Setting the Output Voltages

Set the output voltage on each output by

selecting the resistive voltage divider ratio. The

voltage divider drops the output voltage to the

feedback threshold voltage. Use 10kΩ to 50kΩ

for the low-side resistor RL of the voltage

divider.

For the step-up converter, determine the high-

side resistor RH by the equation:

RH



VMAIN  VFB1



VFB1

RL



Where VMAIN is the output voltage of the step-up

converter.

For the positive charge-pump, determine the

high-side resistor RH by the equation:

RH



VGH  VFB3



VFB3

RL



For the negative charge-pump, determine the

high-side resistor RH by the equation:

RH



VGL



VREF

RL



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, reducing stress on the internal

N-Channel.switch. However, the larger value

inductor has a larger physical size, higher

series resistance, and/or lower saturation

current.

A 4.7µH inductor is recommended for most

applications. A good rule of thumb 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 75% of the current limit to

prevent loss of regulation due to the current

limit. Also make sure that the inductor does not

saturate under the worst-case load transient

and startup conditions.

Calculate the required inductance value by the

equation:

L



VIN  (VOUT - VIN )

VOUT  fSW  I

IIN(MAX)



VOUT ILOAD(MAX)

VIN  

I  30%   50% IIN(MAX)

Where ILOAD(MAX) is the maximum load current, ΔI

is the peak-to-peak inductor ripple current, and η

is efficiency.

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). One 10μF ceramic capacitor is

used in the application circuit of Figure 3

because of the high source impedance seen in

typical lab setups. Actual applications usually

have much lower source impedance since the

step-up converter typically runs directly from the

output of another regulated supply. Typically,

the input capacitance can be reduced below the

value used in the typical application circuit.

To insure stable operation place the input

capacitor as close to the IC as possible.

Alternately a smaller high quality 0.1μF ceramic

capacitor may be placed closer to the IC if the

larger capacitor is placed further away.

MP1530 Rev. 1.41

www.MonolithicPower.com

11

5/25/2011

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© 2011 MPS. All Rights Reserved.

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