z, DUAL-CH, LCD BIAS POWER SUPPLY

MP5610 Rev. 1.02

www.MonolithicPower.com

13

12/6/2016

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APPLICATION INFORMATION

Setting the Positive Output Voltage

The external resistor divider is used to set the

output voltage. Choose the high side feedback

resistor R1 to 100k to 200k resistor, the low side

feedback resistor R2 can be calculated as below,

OUT

R1

R2

V

1

0.6





Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input supply and the switching

noise from the device. The input capacitor

impedance at the switching frequency should be

less than the input source impedance to prevent

the

high-frequency

switching

current

from

passing through to the input. Use ceramic

capacitors with X5R or X7R dielectrics for their

low ESR and small temperature coefficients. For

most applications, use a 1µF-to-4.7

μF ceramic

capacitor.

Selecting the Inductor

The MP5610 requires an inductor to boost its

output voltage. A larger value inductor results in

less ripple current, lowering both the peak-

inductor current and the stress on the internal N-

channel MOSFET. However, the larger inductor

is

physically

larger,

has

a

higher

series

resistance, and a lower saturation current.

Choose an inductor that does not saturate under

the

worst-case

load

conditions.

Select

the

minimum inductor value to ensure that the boost

converter works in continuous-conduction mode

with high efficiency and good EMI performance.

Calculate the required inductance value using the

equation:

2

OUT

SW

LOAD

η V

D (1 D)

L

2

f

I





 





IN

OUT

V

D1

V



the load current, and η is the efficiency.

Selecting the Output Capacitor

The output capacitor keeps the output voltage

ripple small and ensures feedback loop stability.

The output capacitor impedance must be low at

the switching frequency. Ceramic capacitors with

X7R dielectrics are recommended for their low

ESR characteristics. Selection must also account

for the capacitance

’s dependence on the voltage

rating; with a DC bias voltage, the capacitor can

lose as much as 50% of its capacitance at its

rated voltage rating. Leave a sufficient voltage

rating margin when select the component.

Too-low or too-high capacitance will cause loop

instability.

For

most

applications,

select

a

capacitor in the range of 1

μF to 4.7μF.

Selecting Flying Capacitor

The flying capacitor between CP1 and CP2 is

used to transfer energy from step-up converter

switching node to negative output. Ceramic

capacitors

with

X7R

dielectrics

are

recommended for their low ESR characteristics.

Usually, a 0.1

μF to 1μF capacitor can cover most

of the applications.

Layout Consideration

Careful attention must be paid to the PCB board

layout and components placement. Proper layout

of the high frequency switching path is critical to

prevent

noise

and

limit

electromagnetic

interference. The loop consisting of internal low-

side

MOSFET,

synchronous

MOSFET

and

output capacitor contains a high-frequency ripple

current

—minimize this loop. Place the input and

output capacitor should as close to the IC as

possible.