MCP73833 datasheet(13/26 Pages) MICROCHIP

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DS22005A-page 13

MCP73833/4

5.0

DETAILED DESCRIPTION

5.1

Analog Circuitry

5.1.1

BATTERY MANAGEMENT INPUT

SUPPLY (VDD)

The VDD input is the input supply to the MCP73833/4.

The MCP73833/4 automatically enters a Power-down

mode if the voltage on the VDD input falls below the

UVLO voltage (VSTOP). This feature prevents draining

the battery pack when the VDD supply is not present.

5.1.2

CURRENT REGULATION SET

(PROG)

Fast charge current regulation can be scaled by placing

a programming resistor (RPROG) from the PROG input

to VSS. The program resistor and the charge current

are calculated using the Equation 5-1:

EQUATION 5-1:

The preconditioning trickle-charge current and the

charge termination current are ratiometric to the fast

charge current based on the selected device options.

5.1.3

BATTERY CHARGE CONTROL

OUTPUT (VBAT)

The battery charge control output is the drain terminal

of an internal P-channel MOSFET. The MCP73833/4

provides constant current and voltage regulation to the

battery pack by controlling this MOSFET in the linear

region. The battery charge control output should be

connected to the positive terminal of the battery pack.

5.1.4

TEMPERATURE QUALIFICATION

(THERM)

The MCP73833/4 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

Ω negative-temperature coefficient

(NTC) or positive-temperature coefficient (PTC)

thermistors.The current source is controlled, avoiding

measurement sensitivity to fluctuations in the supply

voltage (VDD). The MCP73833/4 compares the voltage

at the THERM pin to factory set thersholds of 1.20V

and 0.25V, typically. Once a volage outside the

thresholds is detected during a charge cycle, the

MCP73833/4 immediately suspends the charge cycle.

The MCP73833/4 suspends charge by turning off the

pass transistor and holding the timer value. The charge

cycle resumes when the voltage at the THERM pin

returns to the normal range.

If temperature monitoring is not required, place a

standard 10 k

Ω resistor from THERM to VSS

5.1.4.1

System Test (LDO) Mode

The MCP73833/4 can be placed in a system test mode.

In this mode, the MCP73833/4 operates as a low

dropout linear regulator (LDO). The output voltage is

regulated to the factory set voltage regulation option.

The available output current is limitted to the

programmed fast charge current. For stability, the VBAT

output must be bypassed to VSS with a minimum

capacitance of 1 µF for output currents up to 250 mA.

A minimum capacitance of 4.7 µF is required for output

currents above 250 mA.

The system test mode is entered by driving the THERM

input greater than (VDD-100 mV) with no battery

connected to the output. In this mode, the MCP73833/4

can be used to power the system without a battery

present.

5.2

Digital Circuitry

5.2.1

STATUS INDICATORS AND POWER

GOOD (PG - OPTION)

The charge status outputs have two different states:

Low (L), and High Impedance (Hi-Z). The charge status

outputs can be used to illuminate LEDs. Optionally, the

charge status outputs can be used as an interface to a

host microcontroller. Table 5-1 summarize the state of

the status outputs during a charge cycle.

IREG

1000V

RPROG

-----------------

Where:

RPROG = kilo-ohms

IREG = milliampere

Note 1: ITHERM is disabled during shutdown,

stand-by, and system test modes.

2: A pull-down current source on the

THERM input is active only in stand-by

and system test modes.

3: During system test mode, the PROG

input sets the available output current

limit.

4: System test mode shall be exited by

releasing the THERM input or cycling

input power.

TABLE 5-1:

STATUS OUTPUTS

CHARGE CYCLE STATE

STAT1

STAT2

Shutdown

Hi-Z

Standby

Hi-Z

Charge in Progress

Hi-Z

Charge Complete (EOC)

Hi-Z

Temperature Fault

Hi-Z

Timer Fault

Hi-Z

System Test Mode

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