Datasheet

2008-2013 Microchip Technology Inc. DS20002090C-page 19
MCP73871
3.13 Low Battery Output (LBO)
STAT1 also serves as low battery output (LBO) if the
selected MCP73871 is equipped with this feature. It
provides an indication to the system or end user when
the Li-Ion battery voltage level is low. The
LBO feature
is enabled when the system is running from the Li-Ion
battery. The
LBO output may be used with an LED or
as an interface to a host microcontroller to signal when
the system is operating from the battery and the battery
is running low on charge. Refer to Table 5-1 for a
summary of the status output during a charge cycle.
3.14 Timer Enable (TE)
The timer enable (TE) feature is used to enable or
disable the internal timer. A low signal enables and a
high signal disables the internal timer on this pin. The
TE input can be used to disable the timer when the sys-
tem load is substantially limiting the available supply
current to charge the battery. The
TE input is compati-
ble with 1.8V logic.
3.15 Battery Temperature Monitor
(THERM)
The MCP73871 device continuously monitors battery
temperature during a charge cycle by measuring the
voltage between the THERM and V
SS
pins. An internal
50 μA current source provides the bias for most
common 10 k Negative Temperature Coefficient
(NTC) thermistors. The MCP73871 device compares
the voltage at the THERM pin to factory set thresholds
of 1.24V and 0.25V, typically. Once a voltage outside
the thresholds is detected during a charge cycle, the
MCP73871 device immediately suspends the charge
cycle. The charge cycle resumes when the voltage at
the THERM pin returns to the normal range. The
charge temperature window can be set by placing fixed
value resistors in series-parallel with a thermistor.
Refer to Section 6.0 “Applications” for calculations
of resistance values.
3.16 Charge Enable (CE)
With the CE input Low, the Li-Ion battery charger
feature of the MCP73871 is disabled. The charger fea-
ture is enabled when CE is active High. Allowing the
CE pin to float during the charge cycle may cause
system instability. The CE input is compatible with 1.8V
logic. Refer to Section 6.0 “Applications” for various
applications in designing with CE features.
3.17 Exposed Thermal Pad (EP)
An internal electrical connection exists between the
Exposed Thermal Pad (EP) and the V
SS
pin. They must
be connected to the same potential on the Printed
Circuit Board (PCB).
Note: The built-in safety timer is available for the
following options: 4 HR, 6 HR and 8 HR.