Rainbow-electronics MAX8724 Uživatelský manuál stáhnout pdf (Strana 21)

The 22µF ceramic capacitor has a typical ESR of

0.003Ω, which sets the output zero at 2.412MHz.

The output pole is set at:

where:

Set the compensation zero (f

Z_CV

) such that it is equiv-

alent to the output pole (f

P_OUT

= 1.08kHz), effectively

producing a pole-zero cancellation and maintaining a

single-pole system response:

Choose C

= 100nF, which sets the compensation

zero (f

Z_CV

) at 1.6kHz. This sets the compensation pole:

CCI Loop Definitions

Compensation of the CCI loop depends on the parame-

ters and components shown in Figure 7. C

is the CCI

loop compensation capacitor. A

CSI

is the internal gain

of the current-sense amplifier. RS2 is the charge cur-

rent-sense resistor, RS2 = 15mΩ. R

OGMI

is the equiva-

lent output impedance of the GMI amplifier ≥ 10MΩ.

GMI is the charge-current amplifier transconductance

= 1µA/mV. GM

OUT

is the DC-DC converter transcon-

ductance = 3.3A/V. The CCI loop is a single-pole sys-

tem with a dominant pole compensation set by f

P_CI

The loop transfer function is given by:

Since:

The loop transfer function simplifies to:

LTF GMI

sR C

OGMI

OGMI CI

=×

+×1

ARS

OUT

CSI

LTF GM A RS GMI

sR C

OUT CSI

OGMI

OGMI CI

=×××

+×

PCI

OGMI CI

2π

PCV

OGMV CV

016

R kHz

2108

147

π .

ZCV

CV CV

2π

Battery ESR

BATT

CHG

∆

kHz

POUT

L OUT

108

MAX1908/MAX8724

Low-Cost Multichemistry Battery Chargers

______________________________________________________________________________________ 21

CCV LOOP GAIN

vs. FREQUENCY

FREQUENCY (Hz)

GAIN (dB)

100k10k1k10010

-40

-20

-60

11M

CCV LOOP PHASE

vs. FREQUENCY

FREQUENCY (Hz)

PHASE (DEGREES)

100k10k1k10010

-120

-105

-90

-75

-60

-45

-135

11M

Figure 6. CCV Loop Gain/Phase vs. Frequency

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 27

MAX1908/MAX8724 1
Package Information 27

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