MCP73871-2AAISLASHML datasheet(25/36 Pages) MICROCHIP

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DS20002090F-page 25

MCP73871

For example, by utilizing a 10 k

 at 25°C NTC

thermistor with a sensitivity index,

, of 3892, the

charge temperature range can be set to 0-50°C by

placing a 1.54 k

 resistor in series (RT1), and a

69.8 k

 resistor in parallel (RT2) with the thermistor.

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

Table 5-1 for a summary of the state of the status

output during a charge cycle.

6.1.1.7

System Load Current

The preferred discharge current for Lithium-Ion cells

should always follow references and guidance from

battery manufacturers. The recommended system

load should be the lesser of 1.0 amperes or the

maximum discharge rate of the selected Lithium-Ion

cell. This limits the safety concerns of power

dissipation

and

exceeding

the

manufacturer’s

maximum discharge rate of the cell.

The ideal diode between VBAT and OUT is designed to

drive a maximum current up to 2A. The built-in thermal

shutdown protection may turn the MCP73871 device

off with high current.

6.1.1.8

Input Overvoltage Protection (IOVP)

The input overvoltage protection must be used when

the input power source is hot-pluggable. This includes

USB cables and wall-type power supplies. The cabling

of these supplies acts as an inductor. When the

supplies are connected/disconnected from the system,

large voltage transients are created and this may

damage the system circuitry. These transients should

be snubbed out. A unidirectional or bidirectional

transzorb connected from the V+ input supply connec-

tor to the 0V ground reference will snub the transients.

An example can be seen in Figure 6-1.

6.2

PCB Layout Issues

For optimum voltage regulation, it is recommended to

place the battery pack closest to the device’s VBAT and

VSS pins to minimize voltage drops along the high

current-carrying PCB traces.

If the PCB layout is used as a heat sink, adding many

vias in the heat sink pad can help conduct more heat to

the PCB backplane, thus reducing the maximum

junction temperature.

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