The 22µF ceramic capacitor has a typical ESR of

0.003

Ω, which sets the output zero at 2.412MHz.

The output pole is set at:

where:

producing a pole-zero cancellation and maintaining a

single-pole system response:

CCI Loop Definitions

Compensation of the CCI loop depends on the parame-

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

rent-sense resistor, RS2 = 15m

lent output impedance of the GMI amplifier

≥ 10MΩ.

GMI is the charge-current amplifier transconductance

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

The loop transfer function is given by:

Since:

The loop transfer function simplifies to:

LTF

GMI

R

sR

C

OGMI

OGMI

CI

=×

+×

1

GM

ARS

OUT

CSI

=

×

1

2

LTF

GM

A

RS

GMI

R

sR

C

OUT

CSI

OGMI

OGMI

CI

=×

×

×

+×

2

1

f

RC

PCI

OGMI

CI

_

=

×

1

2

π

f

RC

Hz

PCV

OGMV

CV

_

.

=

×

=

1

2

016

π

C

R

kHz

nF

CV

CV

=

×

=

1

21 08

147

π

.

f

RC

ZCV

CV

CV

_

=

×

1

2

π

R

V

I

Battery ESR

L

BATT

CHG

==

∆

∆

f

RC

kHz

P OUT

L

OUT

_

.

=

×

=

1

2

108

π

Low-Cost Multichemistry Battery Chargers

______________________________________________________________________________________

21

CCV LOOP GAIN

vs. FREQUENCY

FREQUENCY (Hz)

100k

10k

1k

100

10

-40

-20

0

20

40

60

80

-60

11M

CCV LOOP PHASE

vs. FREQUENCY

FREQUENCY (Hz)

100k

10k

1k

100

10

-120

-105

-90

-75

-60

-45

-135

11M

Figure 6. CCV Loop Gain/Phase vs. Frequency