MIC3263 datasheet(21/32 Pages) MICREL

21 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

3 shows that

Equation

LOAD

D' R

is a right-half plane

PZ):

Equa

zero (fRH

tion 4:

RHP Zero→

LOAD

RHPZ

D' R

2πL

The loop bandwidth should be about 1/10 of t

th t there is

his greatly

fer function

nalyzer.

source. Tie

will operate

g CRV to a

nt DC voltage, this effectively opens the CRV

control loop and allows the measurement of the boost

control loop. GVC(S) can be calculated with a

using the above equation. From the bode plot of GVC(S)

find what the gain of VC(s) is at 1/10 of fRHPZ or

design the error amp gain GEA(s) so the loop g

cross over frequency T(fCO) is 0db where fCO =1

or lower.

Figure 14. Error Amp Transfer Function

The error amp is a gm type and the gain – GEA(S) – is:

Equation 5

he fRHPZ to

ensure stability. From Equation 3, it is shown

only the single pole due to RLOADCOUT. T

simplifies the compensation.

One needs only to get a bode plot of the trans

of the control to output GVC(S) with a network a

To measure GVC(S), tie CRV to a DC voltage

CRV to the steady state voltage that CRV

usually between 1V and 2.4V. By connectin

consta

computer

less. Nex

ain at the

/10 of fRHPZ

Error Amp

⎛⎞

⎜⎟

⎝

gm = 0.056mA/V and ZO = 5MΩ. T

⎠⎠

COMP

G(s) = g

he error amplifier zero is

COMP COMP

Zero

2πRC

. Set the fCO at the mid band

where GEA(fCO) = gm × RCOMP. At fZERO × 10 the phase boost

is near its maximum.

-100

-80

-60

-40

-20

Figure 15. Internal Error Amp and External Compensation

le 1

Conditions: VIN = 12V, VOUT = 29V, IOUT = 0.18A, L = 22μH,

COUT = 4.7μF R

= VOUT/IOUT = 161Ω. When VCRV =

1.8V, the

is:

Examp

LOAD

RHPZ

LOAD

RHPZ

D' R

= 162kH

2πL

Figure 16 shows a plot of:

( )

()

⎛⎞

⎜⎟

⎛⎞

⎝⎠

⎜⎟⎜⎟ ⎛⎞

⎝⎠⎝⎠

⎜⎟

⎝⎠

OUT

CONTROL

LOAD

LOAD OUT

G(s) =

D' R

D'R

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

Freq

Gain

Phase

Midband Gain

Fzero

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