Microchip Technology MCP73213EV-2SOVP Data Sheet
MCP73213
DS22190B-page 22
© 2009 Microchip Technology Inc.
6.1
Application Circuit Design
Due to the low efficiency of linear charging, the most
important factors are thermal design and cost, which
are a direct function of the input voltage, output current
and thermal impedance between the battery charger
and the ambient cooling air. The worst-case situation is
when the device has transitioned from the
Preconditioning mode to the Constant-current mode. In
this situation, the battery charger has to dissipate the
maximum power. A trade-off must be made between
the charge current, cost and thermal requirements of
the charger.
important factors are thermal design and cost, which
are a direct function of the input voltage, output current
and thermal impedance between the battery charger
and the ambient cooling air. The worst-case situation is
when the device has transitioned from the
Preconditioning mode to the Constant-current mode. In
this situation, the battery charger has to dissipate the
maximum power. A trade-off must be made between
the charge current, cost and thermal requirements of
the charger.
6.1.1
COMPONENT SELECTION
is
crucial to the integrity and reliability of the charging
system. The following discussion is intended as a guide
for the component selection process.
system. The following discussion is intended as a guide
for the component selection process.
6.1.1.1
Charge Current
The preferred fast charge current for Li-Ion / Li-Poly
cells is below the 1C rate, with an absolute maximum
current at the 2C rate.
cells is below the 1C rate, with an absolute maximum
current at the 2C rate.
The recommended fast charge
current should be obtained from battery
manufacturer. For example, a 500 mAh battery pack
with 0.7C preferred fast charge current has a charge
current of 350 mA. Charging at this rate provides the
shortest charge cycle times without degradation to the
battery pack performance or life.
manufacturer. For example, a 500 mAh battery pack
with 0.7C preferred fast charge current has a charge
current of 350 mA. Charging at this rate provides the
shortest charge cycle times without degradation to the
battery pack performance or life.
6.1.1.2
Thermal Considerations
The worst-case power dissipation in the battery
charger occurs when the input voltage is at the
maximum and the device has transitioned from the
Preconditioning mode to the Constant-current mode. In
this case, the power dissipation is:
charger occurs when the input voltage is at the
maximum and the device has transitioned from the
Preconditioning mode to the Constant-current mode. In
this case, the power dissipation is:
EQUATION 6-1:
Power dissipation with a 9V, ±10% input voltage
source, 500 mA ±10% and preconditioning threshold
voltage at 6V is:
source, 500 mA ±10% and preconditioning threshold
voltage at 6V is:
EQUATION 6-2:
This power dissipation with the battery charger in the
DFN-10 package will result approximately 92
DFN-10 package will result approximately 92
°C above
room temperature.
6.1.1.3
External Capacitors
The MCP73213 is stable with or without a battery load.
In order to maintain good AC stability in the Constant-
voltage mode, a minimum capacitance of 1 µF is
recommended to bypass the V
In order to maintain good AC stability in the Constant-
voltage mode, a minimum capacitance of 1 µF is
recommended to bypass the V
BAT
pin to V
SS
. This
capacitance provides compensation when there is no
battery load. In addition, the battery and
interconnections appear inductive at high frequencies.
These elements are in the control feedback loop during
Constant-voltage mode. Therefore, the bypass
capacitance may be necessary to compensate for the
inductive nature of the battery pack.
battery load. In addition, the battery and
interconnections appear inductive at high frequencies.
These elements are in the control feedback loop during
Constant-voltage mode. Therefore, the bypass
capacitance may be necessary to compensate for the
inductive nature of the battery pack.
A minimum of 16V rated 1 µF, is recommended to apply
for output capacitor and a minimum of 25V rated 1 µF,
is recommended to apply for input capacitor for typical
applications.
for output capacitor and a minimum of 25V rated 1 µF,
is recommended to apply for input capacitor for typical
applications.
TABLE 6-1:
MLCC CAPACITOR EXAMPLE
Virtually any good quality output filter capacitor can be
used, independent of the capacitor’s minimum
Effective Series Resistance (ESR) value. The actual
value of the capacitor (and its associated ESR)
depends on the output load current. A 1 µF ceramic,
tantalum or aluminum electrolytic capacitor at the
output is usually sufficient to ensure stability.
used, independent of the capacitor’s minimum
Effective Series Resistance (ESR) value. The actual
value of the capacitor (and its associated ESR)
depends on the output load current. A 1 µF ceramic,
tantalum or aluminum electrolytic capacitor at the
output is usually sufficient to ensure stability.
6.1.1.4
Reverse-Blocking Protection
The MCP73213 provides protection from a faulted or
shorted input. Without the protection, a faulted or
shorted input would discharge the battery pack through
the body diode of the internal pass transistor.
shorted input. Without the protection, a faulted or
shorted input would discharge the battery pack through
the body diode of the internal pass transistor.
Note:
Please consult with your battery supplier
or refer to battery data sheet for preferred
charge rate.
or refer to battery data sheet for preferred
charge rate.
PowerDissipation
V
DDMAX
V
PTHMIN
–
(
) I
REGMAX
×
=
Where:
V
DDMAX
=
the maximum input voltage
I
REGMAX
=
the maximum fast charge current
V
PTHMIN
=
the minimum transition threshold
voltage
voltage
MLCC
Capacitors
Temperature
Range
Tolerance
X7R
-55
°C to +125°C
±15%
X5R
-55
°C to +85°C ±15%
PowerDissipation
9.9
V
6.0
V
–
(
) 550mA
×
2.15
W
=
=