LTC4100 Linear Technology, LTC4100 Datasheet - Page 18

• Manufacturer Part Number: LTC4100
• Description: Smart Battery Charger Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC4100
OPERATIO
The AC Present Block (AC_PRESENT)
The DCDIV pin is used to determine AC presence. If the
DCDIV voltage is above the DCDIV comparator threshold
(V
the AC_PRESENT bit in the ChargerStatus() function will
Adapter Limiting
An important feature of the LTC4100 is the ability to
automatically adjust charging current to a level which
avoids overloading the wall adapter. This allows the prod-
uct to operate at the same time that batteries are being
charged without complex load management algorithms.
Additionally, batteries will automatically be charged at the
maximum possible rate of which the adapter is capable.
This feature is created by sensing total adapter output
current and adjusting charging current downward if a
preset adapter current limit is exceeded. True analog
control is used, with closed loop feedback ensuring that
adapter load current remains within limits. Amplifier CL1
in Figure 9 senses the voltage across R
between the CLP and CLN pins. When this voltage exceeds
100mV, the amplifier will override programmed charging
current to limit adapter current to 100mV/R
filter formed by 4.99k and 0.1 F is required to eliminate
switching noise. If the current limit is not used, CLP should
be connected to CLN.
Setting Input Current Limit
To set the input current limit, you need to know the
minimum wall adapter current rating. Subtract 7% for the
18
ACP
*R
LTC4100
), then the ACP output pin will be switched to V
CL
=
ADAPTER CURRENT LIMIT
CL1
Figure 9. Adapter Current Limiting
100mV
–
+
U
U
+
100mV
U
CLP
CLN
INFET
0.1 F
4.99k
W
TO LOAD
R
CL
4100 F09
CL
*
CL
, connected
. A lowpass
U
V
DD
IN
and
be set. If the DCDIV voltage is below the DCDIV compara-
tor threshold minus the DCDIV comparator hysteresis,
then the ACP output pin is switched to GND and the
AC_PRESENT bit in the ChargerStatus() function is cleared.
The ACP output pin is designed to drive 2mA continuously.
input current limit tolerance and use that current to
determine the resistor value.
Table 8. Common R
* Values shown above are rounded to nearest standard value.
As is often the case, the wall adapter will usually have at
least a +10% current limit margin and many times one can
simply set the adapter current limit value to the actual
adapter rating (see Table 8).
Charge Termination Issues
Batteries with constant current charging and voltage-
based charger termination might experience problems
with reductions of charger current caused by adapter
limiting. It is recommended that input limiting feature be
defeated in such cases. Consult the battery manufacturer
for information on how your battery terminates charging.
Setting Output Current Limit (Refer to Figure 1)
The LTC4100 current DAC and the PWM analog circuitry
must coordinate the setting of the charger current. Failure
to do so will result in incorrect charge currents.
RATING (A)
ADAPTER
R
I
LIM
1.5
1.8
2.3
2.5
2.7
CL
2
3
= 100mV/I
= Adapter Min Current –
(Adapter Min Current • 7%)
R
CL
( ) 1%
0.045
0.039
0.036
0.033
CL
0.06
0.05
0.03
VALUE*
LIM
Resistor Values
DISSIPATION (W)
R
CL
0.135
0.162
0.206
0.225
0.241
0.18
0.27
POWER
R
RATING (W)
CL
sn4100 4100is
0.25
0.25
0.25
0.25
POWER
0.5
0.5
0.5