MCP73831-2ACISLASHMC datasheet(13/28 Pages) MICROCHIP

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DS21984E-page 13

MCP73831/2

4.0

DEVICE OVERVIEW

The MCP73831/2 are highly advanced linear charge

management

controllers.

Figure 4-1

depicts

the

operational flow algorithm from charge initiation to

completion and automatic recharge.

FIGURE 4-1:

Flowchart.

4.1

Undervoltage Lockout (UVLO)

An internal UVLO circuit monitors the input voltage and

keeps the charger in Shutdown mode until the input

supply rises above the UVLO threshold. The UVLO

circuitry has a built in hysteresis of 100 mV.

In the event a battery is present when the input power

is applied, the input supply must rise 150 mV above the

battery voltage before the MCP73831/2 becomes oper-

ational.

The UVLO circuit places the device in Shutdown mode

if the input supply falls to within +50 mV of the battery

voltage. Again, the input supply must rise to a level

150 mV

above

the

battery

voltage

before

the

MCP73831/2 become operational.

The UVLO circuit is always active. Whenever the input

supply is below the UVLO threshold or within +50 mV

of the voltage at the VBAT pin, the MCP73831/2 are

placed in a Shutdown mode.

During any UVLO condition, the battery reverse

discharge current will be less than 2 µA.

4.2

Charge Qualification

For a charge cycle to begin, all UVLO conditions must

be met and a battery or output load must be present. A

charge

current

programming

resistor

must

connected from PROG to VSS. If the PROG pin is open

or floating, the MCP73831/2 are disabled and the

battery reverse discharge current is less than 2 µA. In

this manner, the PROG pin acts as a charge enable

and can be used as a manual shutdown.

4.3

Preconditioning

If the voltage at the VBAT pin is less than the precondi-

tioning threshold, the MCP73831/2 enter a precondi-

tioning or Trickle Charge mode. The preconditioning

threshold is factory set. Refer to

Section 1.0 “Electri-

cal Characteristics” for preconditioning threshold

options and the Product Identification System for

standard options.

In this mode, the MCP73831/2 supply a percentage of

the charge current (established with the value of the

resistor connected to the PROG pin) to the battery. The

percentage or ratio of the current is factory set. Refer to

Section 1.0

“Electrical

Characteristics”

for

preconditioning current options and the

”Product

Identification System” for standard options.

When the voltage at the VBAT pin rises above the

preconditioning threshold, the MCP73831/2 enter the

Constant-Current or Fast Charge mode.

4.4

Fast Charge Constant-Current

Mode

During the Constant-Current mode, the programmed

charge current is supplied to the battery or load. The

charge current is established using a single resistor

from PROG to VSS. Constant-Current mode is

maintained until the voltage at the VBAT pin reaches the

regulation voltage, VREG.

SHUTDOWN MODE

VDD < VUVLO

VDD < VBAT

PROG > 200 k

STAT = Hi-Z

PRECONDITIONING

MODE

Charge Current = IPREG

STAT = LOW

FAST CHARGE

MODE

Charge Current = IREG

STAT = LOW

CONSTANT VOLTAGE

MODE

Charge Voltage = VREG

STAT = LOW

VBAT < VPTH

VBAT > VPTH

VBAT = VREG

VBAT < VRTH

VBAT > VPTH

IBAT < ITERM

CHARGE COMPLETE

MODE

No Charge Current

STAT = HIGH (MCP73831)

STAT = Hi-Z (MCP73832)

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