MAX8725ETI+ Maxim Integrated Products, MAX8725ETI+ Datasheet - Page 24

• Manufacturer Part Number: MAX8725ETI+
• Description: IC CHARGER BATTERY 28-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8725ETI+

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 8 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN Exposed Pad
• Product: Charge Management
• Operating Supply Voltage: 8 V to 28 V
• Supply Current: 2.7 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Charge Safety Timers: No
• Mounting Style: SMD/SMT
• Temperature Monitoring: No
• Uvlo Start Threshold: 9.18 V
• Uvlo Stop Threshold: 9.42 V
• 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