MCP73831 Microchip Technology, Inc., MCP73831 Datasheet - Page 14

• Manufacturer Part Number: MCP73831
• Manufacturer: Microchip Technology, Inc.

MCP73831
Power dissipation with a 5V, ±10% input voltage source
is:
This power dissipation with the battery charger in the
SOT23-5 package will cause thermal regulation to be
entered as depicted in Figure 6-3. Alternatively, the
2mm x 3mm DFN package could be utilized to reduce
charge cycle times.
6.1.1.3
The MCP73831 is stable with or without a battery load.
In order to maintain good AC stability in the Constant-
Voltage mode, a minimum capacitance of 4.7 F is
recommended to bypass the V
capacitance provides compensation when there is no
battery load. In addition, the battery and interconnec-
tions appear inductive at high frequencies. These
elements are in the control feedback loop during
Constant-Voltage mode. Therefore, the bypass capac-
itance may be necessary to compensate for the
inductive nature of the battery pack.
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 4.7 F ceramic,
tantalum or aluminum electrolytic capacitor at the
output is usually sufficient to ensure stability for output
currents up to a 500 mA.
6.1.1.4
The MCP73831 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.
6.1.1.5
The current regulation set input pin (PROG) can be
used to terminate a charge at any time during the
charge cycle, as well as to initiate a charge cycle or
initiate a recharge cycle.
DS21984A-page 14
Where:
PowerDissipation
I
V
PowerDissipation
V
REGMAX
PTHMIN
DDMAX
External Capacitors
Reverse-Blocking Protection
Charge Inhibit
= the maximum input voltage
= the maximum fast charge current
= the minimum transition threshold
voltage
=
=
V
DDMAX
5.5V 2.7V
–
–
V
PTHMIN
BAT
550mA
pin to V
I
REGMAX
=
1.54W
SS
. This
Placing a programming resistor from the PROG input to
V
float or by applying a logic-high input signal, disables
the device and terminates a charge cycle. When
disabled, the device’s supply current is reduced to
25 A, typically.
6.1.1.6
A status output provides information on the state of
charge. The output can be used to illuminate external
LEDs or interface to a host microcontroller. Refer to
Table 5-1 for a summary of the state of the status
output during a charge cycle.
6.2
For optimum voltage regulation, place the battery pack
as close as possible to the device’s V
This is recommended to minimize voltage drops along
the high current-carrying PCB traces.
If the PCB layout is used as a heatsink, adding many
vias in the heatsink pad can help conduct more heat to
the backplane of the PCB, thus reducing the maximum
junction temperature. Figures 6-4 and 6-5 depict a
typical layout with PCB heatsinking.
FIGURE 6-4:
FIGURE 6-5:
SS
enables the device. Allowing the PROG input to
PCB Layout Issues
V
V
V
V
SS
BAT
SS
BAT
Charge Status Interface
C
OUT
Typical Layout (Top).
Typical Layout (Bottom).
R
MCP73831
© 2005 Microchip Technology Inc.
LED
LED
R
C
PROG
IN
BAT
and V
V
V
DD
DD
SS
pins.