Rainbow-electronics MAX8724 Instrukcja Użytkownika Pobierz pdf (Strona 22)

MAX1908/MAX8724

The crossover frequency is given by:

The CCI loop dominant compensation pole:

where the GMI amplifier output impedance, R

OGMI

10MΩ.

To calculate the CCI loop compensation pole, C

GMI = 1µA/mV

OUT

= 3.33A/V

OGMI

= 10MΩ

f = 400kHz

Choose crossover frequency f

CO_

to be 1/5th the

MAX1908/MAX8724 switching frequency:

Solving for C

, C

= 2nF.

To be conservative, set C

= 10nF, which sets the

crossover frequency at:

The compensation pole, f

P_CI

is set at:

CCS Loop Definitions

Compensation of the CCS loop depends on the parame-

ters and components shown in Figure 9. C

is the CCS

loop compensation capacitor. A

CSS

is the internal gain of

the current-sense amplifier. RS1 is the input current-

sense resistor, RS1 = 10mΩ. R

OGMS

is the equivalent

output impedance of the GMS amplifier ≥ 10MΩ. GMS is

GMI

PCI

OGMI CI

0 0016

GMI

kHz

CO CI_

210

GMI

kHz

CO CI

PCI

OGMI CI

2π

GMI

CO CI

2π

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22 ______________________________________________________________________________________

OUT

CCI

GMI

ICTL

OGMI

CSIP CSIN

CSI

RS2

Figure 7. CCI Loop Diagram

CCI LOOP GAIN

vs. FREQUENCY

FREQUENCY (Hz)

GAIN (dB)

100k10k110100 1k

-40

-20

100

-60

0.1 1M

CCI LOOP PHASE

vs. FREQUENCY

FREQUENCY (Hz)

PHASE (DEGREES)

100k10k1k100101

-90

-75

-60

-45

-30

-15

-105

0.1 1M

Figure 8. CCI Loop Gain/Phase vs. Frequency

1 2 ... 17 18 19 20 21 22 23 24 25 26 27

MAX1908/MAX8724 1
Package Information 27

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