MCP73827-4.2VUA Просмотр технического описания (PDF) - Microchip Technology

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MCP73827-4.2VUA

Single Cell Lithium-Ion Charge Management Controller with Mode Indicator and Charge Current Monitor

Microchip Technology 

MCP73827

5.0 DETAILED DESCRIPTION

Refer to the typical application circuit, Figure 6-1.

5.1 Analog Circuitry

5.1.1 CHARGE CURRENT MONITOR (IMON)

The IMON pin provides an output voltage that is propor-

tional to the battery charging current. It is an amplified

version of the sense resistor voltage drop that the cur-

rent loop uses to control the external P-channel pass

transistor. This voltage signal can be applied to the

input of an A/D Converter and used by a host microcon-

troller to display information about the state of the bat-

tery or charge current profile.

5.1.2 CELL VOLTAGE MONITORED INPUT

(VBAT)

The MCP73827 monitors the cell voltage at the VBAT

pin. This input is tied directly to the positive terminal of

the battery. The MCP73827 is offered in two fixed-volt-

age versions for single cells with either coke or graphite

anodes: 4.1V (MCP73827-4.1) and 4.2V

(MCP73827-4.2).

5.1.3 GATE DRIVE OUTPUT (VDRV)

The MCP73827 controls the gate drive to an external

P-channel MOSFET, Q1. The P-channel MOSFET is

controlled in the linear region, regulating current and

voltage supplied to the cell. The drive output is auto-

matically turned off when the input supply falls below

the voltage sensed on the VBAT input.

5.1.4 CURRENT SENSE INPUT (VSNS)

Fast charge current regulation is maintained by the

voltage drop developed across an external sense resis-

tor, RSENSE, applied to the VSNS input pin. The follow-

ing formula calculates the value for RSENSE:

RSENSE

=

--V----C---S--

IOUT

Where:

VCS is the current limit threshold

IOUT is the desired peak fast charge current in

amps. The preconditioning current is scaled to

approximately 43% of IPEAK.

5.1.5 SUPPLY VOLTAGE (VIN)

The VIN input is the input supply to the MCP73827. The

MCP73827 automatically enters a power-down mode if

the voltage on the VIN input falls below the voltage on

the VBAT pin. This feature prevents draining the battery

pack when the VIN supply is not present.

5.2 Digital Circuitry

5.2.1 SHUTDOWN INPUT (SHDN)

The shutdown input pin, SHDN, can be used to termi-

nate a charge anytime during the charge cycle, initiate

a charge cycle, or initiate a recharge cycle.

Applying a logic High input signal to the SHDN pin, or

tying it to the input source, enables the device. Apply-

ing a logic Low input signal disables the device and ter-

minates a charge cycle. In shutdown mode, the

device’s supply current is reduced to 0.5 µA, typically.

5.2.2 CHARGE STATUS OUTPUT (MODE)

A charge status output, MODE, provides information on

the state of charge. The open drain output can be used

to illuminate an external LED. Optionally, a pull-up

resistor can be used on the output for communication

with a microcontroller. Table 5-1 summarizes the state

of the charge status output during a charge cycle.

Charge Cycle State

Qualification

Preconditioning

Controlled Current Fast Charge

Constant Voltage

Disabled - Sleep mode

Battery Disconnected

TABLE 5-1: Charge Status Output.

Mode

OFF

ON

ON

OFF

OFF

OFF

DS21704B-page 10

© 2007 Microchip Technology Inc.

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