MCP73871 datasheet(16/36 Pages) MICROCHIP

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MCP73871

DS20002090F-page 16

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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

compatible with 1.8V logic. The TE signal asserted low

will stop the timer but not Reset it. The timer can be

reset by cycling the CE pin. The second character of

the operational output options code indicates the Timer

interval: A = disable, B = 4 hours, C = 6 hours and D =

8 hours.

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 VSS 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

feature 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 VSS 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.

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