MCP73223-22SI/MF MICROCHIP [Microchip Technology], MCP73223-22SI/MF Datasheet - Page 22

• Manufacturer Part Number: MCP73223-22SI/MF
• Description: Lithium Iron Phosphate (LiFePO4) Battery Charge Management Controller with Input Overvoltage Protection
• Manufacturer: MICROCHIP [Microchip Technology]

MCP73123/223
6.1
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
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
Selection of the external components in
crucial to the integrity and reliability of the charging
system. The following discussion is intended as a guide
for the component selection process.
6.1.1.1
The recommended fast charge current should be
obtained from battery manufacturer. For example, a
1000 mAh battery pack with 2C preferred fast charge
current has a charge current of 1000 mA. Charging at
this rate provides the shortest charge cycle times
without degradation to the battery pack performance or
life.
6.1.1.2
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:
EQUATION 6-1:
DS22191A-page 22
Where:
Note:
I
V
PowerDissipation
V
REGMAX
PTHMIN
DDMAX
the
Application Circuit Design
COMPONENT SELECTION
Please consult with your battery supplier
or refer to battery data sheet for preferred
charge rate.
Charge Current
Thermal Considerations
device
= the maximum input voltage
= the maximum fast charge current
= the minimum transition threshold
voltage
=
(
V
DDMAX
has
transitioned
–
V
PTHMIN
)
×
Figure 6-1
I
REGMAX
from
the
is
Power dissipation with a 5V, ±10% input voltage
source, 500 mA ±10% and preconditioning threshold
voltage at 2V is:
EQUATION 6-2:
This power dissipation with the battery charger in the
DFN-10 package will result approximately 83°C above
room temperature.
6.1.1.3
The MCP73123/223 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
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
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.
TABLE 6-1:
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.
6.1.1.4
The MCP73123/223 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.
Capacitors
PowerDissipation
MLCC
X7R
X5R
External Capacitors
Reverse-Blocking Protection
-55°C to +125°C
-55°C to +85°C
Temperature
MLCC CAPACITOR EXAMPLE
mode.
=
Range
(
© 2009 Microchip Technology Inc.
5.5V 2V
–
Therefore,
)
×
550mA
BAT
Tolerance
the
±15%
±15%
=
pin to V
1.925W
bypass
SS
.