MAX8731AETI+T Maxim Integrated Products, MAX8731AETI+T Datasheet - Page 23

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

Specifications of MAX8731AETI+T

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

control point. Clamping the other two control loops
close to the lowest control loop ensures fast transition
with minimal overshoot when switching between differ-
ent control loops (see the Compensation section).
With sufficient charge current, the MAX8731A’s induc-
tor current never crosses zero, which is defined as con-
tinuous-conduction mode. The regulator switches at
400kHz (nominal) if V
troller starts a new cycle by turning on the high-side
MOSFET and turning off the low-side MOSFET. When
the charge-current feedback signal (CSI) is greater
than the control point (LVC), the CCMP comparator out-
put goes high and the controller initiates the off-time by
turning off the high-side MOSFET and turning on the
low-side MOSFET. The operating frequency is gov-
erned by the off-time and is dependent upon V
V
The on-time can be determined using the following
equation:
where:
The switching frequency can then be calculated:
These equations describe the controller’s pseudo-
fixed-frequency performance over the most common
operating conditions.
At the end of the fixed off-time, the controller initiates a
new cycle if the control point (LVC) is greater than
100mV and the peak charge current is less than the
cycle-by-cycle current limit. Restated another way,
CSSP
. The off-time is set by the following equation:
t
OFF
I
t
RIPPLE
Continuous-Conduction Mode
ON
______________________________________________________________________________________
=
f
SW
2 5 . μ
=
CSIN
V
=
CSSN
=
s
L I
t
×
ON
V
×
BATT
V
< 0.88 x V
RIPPLE
CSSP
+
−
1
SMBus Level 2 Battery Charger
t
V
V
OFF
L
BATT
CSSP
×
t
−
OFF
V
CSIN
CSSP
. The con-
CSIN
and
IMIN must be high, IMAX must be low, and OVP must
be low for the controller to initiate a new cycle. If the
peak inductor current exceeds the IMAX comparator
threshold or the output voltage exceeds the OVP
threshold, then the on-time is terminated. The cycle-by-
cycle current limit effectively protects against overcur-
rent and short-circuit faults.
If during the off-time the inductor current goes to zero,
the ZCMP comparator output pulls high, turning off the
low-side MOSFET. Both the high- and low-side
MOSFETs are turned off until another cycle is ready to
begin. ZCOMP causes the MAX8731A to enter into dis-
continuous-conduction mode (see the Discontinuous
Conduction section).
There is a 0.3µs minimum off-time when the (V
V
V
reached. The switching frequency in this mode varies
according to the equation:
The MAX8731A can also operate in discontinuous-con-
duction mode to ensure that the inductor current is
always positive. The MAX8731A enters discontinuous-
conduction mode when the output of the LVC control
point falls below 100mV. This corresponds to peak
inductor current = 500mA:
charge current for RS2 = 10mΩ.
In discontinuous mode, a new cycle is not started until
the LVC voltage rises above 100mV. Discontinuous-
mode operation can occur during conditioning charge
of overdischarged battery packs, when the charge cur-
rent has been reduced sufficiently by the CCS control
loop, or when the charger is in constant-voltage mode
with a nearly full battery pack.
CSIN
CSSP
with Remote Sense
) differential becomes too small. If V
, the threshold for the 0.3µs minimum off-time is
f
I
CHG
=
V
CSSN
L I
=
Discontinuous Conduction
×
2
1
RIPPLE
×
−
20
V
100
BATT
1
×
mV
RS
+
2
0 3 . μ
=
250
s
mA
CSIN
≥ 0.88 x
CSSP
23
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