Microchip Technology MCP7383XRD-PPM Data Sheet
MCP73831/2
DS20001984F-page 18
2005-2013 Microchip Technology Inc.
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:
Power dissipation with a 5V, ±10% input voltage source
is:
is:
This power dissipation with the battery charger in the
SOT-23-5 package will cause thermal regulation to be
entered as depicted in
SOT-23-5 package will cause thermal regulation to be
entered as depicted in
. Alternatively, the
2mm x 3mm DFN package could be utilized to reduce
charge cycle times.
charge cycle times.
6.1.1.3
External Capacitors
The MCP73831/2 are 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 µF is recommended to bypass the V
load. In order to maintain good AC stability in the
Constant-Voltage mode, a minimum capacitance of
4.7 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.
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 µF ceramic,
tantalum or aluminum electrolytic capacitor at the
output is usually sufficient to ensure stability for output
currents up to a 500 mA.
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.
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 µF 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
Reverse-Blocking Protection
The MCP73831/2 provide 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.
6.1.1.5
Charge Inhibit
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.
Placing a programming resistor from the PROG input to
V
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.
Placing a programming resistor from the PROG input to
V
SS
enables the device. Allowing the PROG input to
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 µA, typically.
the device and terminates a charge cycle. When
disabled, the device’s supply current is reduced to
25 µA, typically.
6.1.1.6
Charge Status Interface
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
charge. The output can be used to illuminate external
LEDs or interface to a host microcontroller. Refer to
for a summary of the state of the status
output during a charge cycle.
6.2
PCB Layout Issues
For optimum voltage regulation, place the battery pack
as close as possible to the device’s V
as close as possible to the device’s V
BAT
and V
SS
pins.
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 PCB backplane, thus reducing the maximum
junction temperature.
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 PCB backplane, thus reducing the maximum
junction temperature.
and
depict
a typical layout with PCB heatsinking.
FIGURE 6-4:
Typical Layout (Top).
FIGURE 6-5:
Typical Layout (Bottom).
PowerDissipation
VDDMAX VPTHMIN
–
(
) IREGMAX
×
=
Where:
V
DDMAX
= the maximum input voltage
I
REGMAX
= the maximum fast charge current
V
PTHMIN
= the minimum transition threshold
voltage
PowerDissipation
5.5V 2.7V
–
(
) 550mA
×
1.54W
=
=
C
OUT
LED
R
PROG
C
IN
MCP73831
R
LED
V
BAT
V
DD
V
SS
V
BAT
V
SS
V
DD