MAX8731AETI+ Maxim Integrated Products, MAX8731AETI+ Datasheet - Page 26

• Manufacturer Part Number: MAX8731AETI+
• Description: IC SMBUS LVL2 BATT CHRGR 28TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8731AETI+

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 8 V ~ 26 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN Exposed Pad
• Product: Charge Management
• Output Voltage: 5.4 V
• Operating Supply Voltage: 8 V to 26 V
• Supply Current: 2 uA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Charge Safety Timers: Yes
• Mounting Style: SMD/SMT
• Temperature Monitoring: No
• Uvlo Start Threshold: 2.5 V
• Uvlo Stop Threshold: 100 mV
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SMBus Level 2 Battery Charger
with Remote Sense
The loop-transfer function is given by:
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
1/10 the switching frequency:
C
ing frequency.
Values for C
can slow down the current-loop response. Choosing C
= 10nF yields a crossover frequency of 15.9kHz.
10
response using the values calculated above.
Figure
26
CI
LTF GM
shows the Bode plot of the current-loop frequency
> 10 × GMI / (2π f
______________________________________________________________________________________
10. CCI Loop Response
=
100
-20
-40
80
60
40
20
0
OUT
CI
0.1
LTF GMI
greater than 10 times the minimum value
×
=
GM
A
CSI
f
OUT
CO CI
10
OSC
1
FREQUENCY (Hz)
×
_
+
RS
=
sR
) = 4nF, for a 400kHz switch-
2
A
R
=
OGMI
×
CSI
OGMI
2π
1k
GMI
GMI
1
C
×
CI
×
RS
1
C
+
2
CI
MAG
PHASE
sR
100k
R
OGMI
OGMI
0
-45
-90
×
C
CI
Figure
CI
The simplified schematic in
describe the operation of the MAX8731A 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 resistor; RS1 = 10mΩ
in the typical application circuits. R
lent output impedance of the GMS amplifier, which is
greater than 10MΩ. GMS is the charge-current amplifier
transconductance = 1µA/mV. GM
verter’s input-referred transconductance = (1/D) x
GM
The loop-transfer function is given by:
Since:
the loop-transfer function simplifies to:
Figure
LTF GM
OUT
11. CCS Loop Diagram
=
= (1 / D) x 5A/V.
InputCurrent( )
IN
CCS
LTF GMS
×
A
=
GMS
CSS
GM
C
CS
IN
×
RSI GMS
1
R
=
OGMS
+
SR
×
A
CCS Loop Compensation
CSS
R
OGMS
Figure 11
OGMS
GM
CSS
1
IN
×
IN
1
RS
OGMS
+
×
is the DC-DC con-
SR
C
2
CS
ADAPTER
R
SYSTEM
OGMS
INPUT
LOAD
is sufficient to
OGMS
is the equiva-
CSSP
CSSI
RS1
CSS
×
C
CS
is the