MP23701 – 24V, 2A, 1.5MHZ, SYNCHRONOUS, STEP-DOWN, LED DRIVER

MP23701 Rev. 1.0

www.MonolithicPower.com

13

3/22/2019

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APPLICATION INFORMATION

Setting the LED Current

A current sense resistor is inserted between the

anode of LED and GND. The current sense

resistor value can be calculated with Equation

(1):

S

LED

0.1V

R

I



(1)

For a 2A LED current output, RS is 50mΩ.

Selecting the Inductor

An inductor less than 100µH with a nominal DC

current rating at least 25% higher than the

maximum load current is recommended for

most applications. For the highest efficiency,

the inductor’s DC resistance should be less

than 100mΩ. For most designs, the required

inductance value can be derived from Equation

(2):

OUT

IN

OUT

IN

L

SW

V(V

V

)

L

VI

f





 

(2)

Where ∆IL is the inductor ripple current.

Choose the inductor ripple current to be 30% of

the maximum load current. The maximum

inductor peak current can be calculated with

Equation (3):

L

L(MAX)

LED

I

II

2





(3)

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 source impedance to prevent

the high-frequency switching current from

passing through the input. Ceramic capacitors

with X5R or X7R dielectrics are highly

recommended because of their low ESR and

small

temperature

coefficients.

For

most

applications, a 10µF capacitor is sufficient.

Selecting the Output Capacitor

The output capacitor keeps the output current

ripple small and ensures feedback loop stability.

The output capacitor impedance should be low

at the switching frequency. Ceramic capacitors

with X5R or X7R dielectrics are recommended

for their low ESR characteristics. For most

applications, a 10µF ceramic capacitor is

sufficient.

PCB Layout Guidelines

Efficient PCB layout is critical for stable

operation. For best results, follow the guidelines

below.

1. Place the high-current paths (GND, VIN,

and SW) very close to the device with short,

direct, and wide traces.

2. Place the input capacitor as close to VIN

and GND as possible.

3. Place the external feedback resistors next

to FB.

4. Keep the switch node traces short and away

from the feedback network.

For more information, please refer to the related

evaluation board datasheet.