MAX1909ETI-T Maxim Integrated Products, MAX1909ETI-T Datasheet - Page 24
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MAX1909ETI-T
Manufacturer Part Number
MAX1909ETI-T
Description
Battery Management
Manufacturer
Maxim Integrated Products
Datasheet
1.MAX1909ETI.pdf
(30 pages)
Specifications of MAX1909ETI-T
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
Multichemistry Battery Chargers with Automatic
System Power Selector
This describes a single-pole system. Since:
the loop transfer function simplifies to:
The crossover frequency is given by:
For stability, choose a crossover frequency lower than
1/10th of the switching frequency:
Choosing a crossover frequency of 30kHz and using the
component values listed in Figure 1 yields C
Values for C
may slow down the current-loop response excessively.
Figure 8 shows the Bode plot of the current-loop fre-
quency response using the values calculated above.
Figure 7. CCI Loop Diagram
24
______________________________________________________________________________________
CCI
C
CI
CI
LTF GMI
greater than 10 times the minimum value
C
GM
=
CI
R
OGMI
OUT
f
CO CI
= GMI / (2π f
1
_
GM
GMI
+
=
sR
OUT
A
=
R
OGMI
CSI
2π
OGMI
GMI
C
1
×
O_CI
ICTL
CI
RS
×
CSIP
C
2
)
CI
CSI
RS2
CSIN
CI
> 5.4nF.
The simplified schematic in Figure 9 is sufficient to
describe the operation of the MAX1909/MAX8725 when
the input current-limit loop (CCS) is in control. Since the
output capacitor’s impedance has little effect on the
response of the input current-limit loop, only a single
pole is required to compensate this loop. A
internal gain of the current-sense amplifier. RS1 is the
input current-sense resistor; RS1 = 10mΩ in the typical
operating circuits. R
impedance of the GMS amplifier, which is greater than
10MΩ. GMS is the input current amplifier transconduc-
tance = 1µA/mV. GM
referred transconductance = (1/D) GM
3.3A/V.
Figure 8. CCI Loop Response
Figure 9. CCS Loop Diagram
CCS
100
-20
-40
CLS
80
60
40
20
0
0.1
GMS
C
CS
IN
R
OGMS
10
OGMS
is the DC-DC converter’s input-
FREQUENCY (Hz)
CCS Loop Compensation
is the equivalent output
CSS
GM
1k
IN
ADAPTER
SYSTEM
INPUT
LOAD
MAG
PHASE
100k
CSSP
CSSN
RS1
OUT
CSS
0
-45
-90
= (1/D)
is the