MP24830 datasheet(11/15 Pages) MPS

11 / 15 page

MP24830 — 4.5V–90V, PROGRAMABLE FREQUENCY WHITE LED DRIVER

MP24830 Rev. 1.0

www.MonolithicPower.com

10/30/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

Figure 4: RCC Compensation Network on COMP

(1)Compensation network for Buck-boost

application

The DC modulator gain of the buck-boost

power stage (from the output current to the

control voltage on COMP pin) is:

OUT

LED

OUT

DCGain _ PS

* V

20 R

(

) (R

)

















Where RCS is the switch current sensing resistor

on CS pin, RLED is the equivalent dynamic

resistance of the LED load, as shown in Figure

ΔILED

ΔVLED

LED





Figure 5: LED Dynamic Resistance Equivalent

The dominant low-frequency pole of the buck-

boost power stage is:

OUT

LED

OUT

P_ PS

OUT

* V









The right-half plane (RHP) zero of the buck-

boost power stage is:

Z_ RHP

OUT

2L I

V )



 





Step 1: Select RCOMP

Choose a crossing frequency, fC, below

1/3×fZ_RHP to derive the compensation network

as follow (assume CZ>>Cp):

COMP

P _ PS

gm R

DCGain _ PS * f





That is:

OUT

LED

OUT

COMP

20 R

)(V

V )

gm R











Use the maximum input voltage and minimum

output voltage to calculate RCOMP.

Step 2: Select CZ

Set the zero of the compensation network to

cancel the minimum pole of the power stage to

get:

P_ PS

COMP







Choose CZ with the maximum input voltage and

maximum output voltage.

Step 3: Select CP

Set the pole of the compensation network to

cancel the minimum RHP zero to get:

z_ RHP

COMP







Choose CP with the minimum input voltage and

maximum output voltage.

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