MAX1535 Maxim Integrated Products, MAX1535 Datasheet - Page 29

• Manufacturer Part Number: MAX1535
• Description: Highly Integrated Level 2 Smbus Battery Charger
• Manufacturer: Maxim Integrated Products

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Additionally, R
and dominates the series combination of R
so:
C
crossover so the parallel impedance is mostly capaci-
tive and:
If R
a negligible effect near crossover and the loop-transfer
function can be simplified as follows:
Setting the LTF = 1 to solve for the unity-gain frequency
yields:
For stability, choose a crossover frequency lower than
1/10th of the switching frequency. For example, choose
a crossover frequency of 30kHz and solving for R
using the component values listed in Figure 1 yields
R
V
GMV = 0.125µA/mV
I
GM
C
f
R
f
CHG
OSC
CO_CV
BATT
CV
L
OUT
OUT
= 0.2Ω
ESR
OUT
= 20kΩ:
= 400kHz
= 4A
= 2 × 22µF
= 16.8V
is also much lower impedance than R
= 30kHz
is small enough, its associated output zero has
= 3.33A/V
f
CO CV
R
R
CV
_
OGMV
LTF GM
CV
(
(
1
1
=
+
+
=
2
is much higher impedance than C
SC
SC
=
______________________________________________________________________________________
π
GM
× +
GMV GM
×
OUT
(
CV
R
C
1
OUT
L
OUT
OUT
×
SC
×
×
R
×
R
CV
OGMV
×
×
L
GMV
f
CO CV
)
SC
OUT
×
R
≅
R
_
CV
OUT
)
SC
CV
×
2π
Highly Integrated Level 2 SMBus
1
OUT
)
=
GMV
≅
R
×
10
R
CV
C
k
CV
OUT
CV
Ω
and C
L
near
CV
CV
CV
,
To ensure that the compensation zero adequately can-
cels the output pole, select f
C
C
current)
Figure 11 shows the Bode plot of the voltage-loop fre-
quency response using the values calculated above.
Figure 9. DC-to-DC Converter Block Diagram
Figure 10. CCV Loop Diagram
CV
CV
LVC
CSI
100mV
50mV
DCIN
BATT
≥ (R
2V
≥ 4nF (assuming 4 cells and 4A maximum charge
CCV
R
L
C
CV
/R
CV
CV
CCMP
ZCMP
COMPUTE
IMAX
OFF-TIME
IMIN
) C
Battery Charger
OUT
R
OGMV
GMV
GM
OUT
ONE-SHOT
OFF-TIME
Z_CV
R
R
REF
≤ f
BATT
P_OUT
Q
Q
R
C
:
ESR
OUT
R
TO
DH
DRIVER
TO
DL
DRIVER
L
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