MCP73826 Microchip Technology, MCP73826 Datasheet - Page 13

• Manufacturer Part Number: MCP73826
• Description: Single Cell Lithium-Ion Charge Management Controller
• Manufacturer: Microchip Technology

Worst case, V
source, 100 m , 1% sense resistor, and a maximum
sink voltage of 1.6V is:
At this worst case, V
must be low enough as to not impede the performance
of the charging system. The maximum allowable
R
The Fairchild NDS8434 and International Rectifier
IRF7404 both satisfy these requirements.
6.1.1.3
The MCP73826 is stable with or without a battery load.
In order to maintain good AC stability in the constant
voltage mode, a minimum capacitance of 10 µF is rec-
ommended to bypass the
itance 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 nec-
essary 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 ESR
(Effective Series Resistance) value. The actual value of
the capacitor and its associated ESR depends on the
forward trans conductance, g
external pass transistor. A 10 µF tantalum or aluminum
electrolytic capacitor at the output is usually sufficient
to ensure stability for up to a 1 A output current.
6.1.1.4
The optional reverse blocking protection diode
depicted in Figure 6-1 provides protection from a
faulted or shorted input or from a reversed polarity input
source. Without the protection diode, a faulted or
shorted input would discharge the battery pack through
the body diode of the external pass transistor.
R
DSON
2002 Microchip Technology Inc.
DSON
V
V
I
R
R
OUT
GS
INMIN
SENSE
DSON
at the worst case V
=
=
is the maximum peak fast charge current
1.6V
EXTERNAL CAPACITORS
REVERSE BLOCKING PROTECTION
4.5V 758mA
------------------------------------------------------------------------------- -
is the minimum input voltage source
=
is the sense resistor
V
------------------------------------------------------------------------------------------ -
GS
–
INMIN
–
4.5V 758mA
with a 5V, +/-10% input voltage
GS
–
758mA
–
I
, the R
OU T
V
GS
BAT
99m
m
I
is:
OU T
pin to GND. This capac-
, and capacitance of the
R
DSON
SENSE
–
99m
4.242V
of the MOSFET
–
V
BATMAX
=
=
–
242m
2.8
V
If a reverse protection diode is incorporated in the
design, it should be chosen to handle the peak fast
charge current continuously at the maximum ambient
temperature. In addition, the reverse leakage current of
the diode should be kept as small as possible.
6.1.1.5
In the stand-alone configuration, the shutdown pin is
generally tied to the input voltage. The MCP73826 will
automatically enter a low power mode when the input
voltage is less than the output voltage reducing the bat-
tery drain current to 8 µA, typically.
By connecting the shutdown pin as depicted in
Figure 6-1, the battery drain current may be further
reduced. In this application, the battery drain current
becomes a function of the reverse leakage current of
the reverse protection diode.
6.2
For optimum voltage regulation, place the battery pack
as close as possible to the device’s
It 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 around the external pass transistor can help con-
duct more heat to the back-plane of the PCB, thus
reducing the maximum junction temperature.
PCB Layout Issues
SHUTDOWN INTERFACE
MCP73826
V
BAT
DS21705A-page 13
and GND pins.