MP1541 – 1.3MHz BOOST CONVERTER

MP1541 Rev.1.3

www.MonolithicPower.com

6

3/20/2006

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© 2006 MPS. All Rights Reserved.

Compensation

The MP1541 uses an amplifier to compensate

the feedback loop rather than a traditional

transconductance amplifier like most current

mode regulators. Frequency compensation is

provided by an internal resistor and capacitor

along with an external resistor. The system

uses two poles and one zero to stabilize the

internal compensation capacitor Cc, the gain of

the error amplifier and the resistance seen

determined by the equations:

LOAD

1

P

R

2

C

1

f

×

×

π

=

()

EQ

9

2

P

R

10

9

.

7

2

1

f

×

×

×

π

×

=

−

kHz

20

)

2

R

1

R

(

)

2

R

1

R

(

3

R

+

×

+

=

Where R1, R2, and R3 are seen in Figure 2.

The DC loop gain is:

2

OUT

FB

LOAD

IN

VDC

V

V

R

V

500

A

∗

∗

∗

=

exists in all continuous mode (inductor current

does not drop to zero on each cycle) step up

converters. The frequency of the right half plane

zero is:

2

OUT

LOAD

2

IN

RHPZ

V

L

2

R

V

f

×

×

π

×

×

=

To stabilize the regulation control loop, the

crossover frequency (the frequency where the

loop gain drops to 0dB or a gain of 1, indicated

right-half-plane zero and should be at most

minimum) and minimum input voltage.

For the MP1541 it is recommended that a 47kΩ

to 100kΩ resistor be placed in series with the FB

pin and the resistor divider as seen in Figure 2.

For most applications this is all that is needed for

stable operation. If greater phase margin is

needed a series resistor and capacitor can be

placed in parallel with the high-side resistor R1 as

seen in Figure 2. The pole and zero set by the

lead-lag compensation network are:

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

+

+

+

×

×

π

×

=

3

R

1

2

R

1

1

R

1

1

4

R

3

C

2

1

P

()

4

R

1

R

3

C

2

1

Z

+

×

×

π

×

=

LAYOUT CONSIDERATIONS

High frequency switching regulators require

very careful layout for stable operation and low

noise. All components must be placed as close

to the IC as possible. Keep the path between

L1, D1, and C2 extremely short for minimal

noise and ringing. C1 must be placed close to

the IN pin for best decoupling. All feedback

components must be kept close to the FB pin to

prevent noise injection on the FB pin trace. The

ground return of C1 and C2 should be tied

close to the GND pin. See the MP1541 demo

board layout for reference.