MCP73853 datasheet(14/24 Pages) MICROCHIP

14 / 24 page

MCP73853/55

DS21915A-page 14

 2004 Microchip Technology Inc.

5.1.6

BATTERY VOLTAGE SENSE (VBAT3)

The MCP73853 monitors the battery voltage at the

VBAT3 pin. This input is tied directly to the positive

terminal of the battery pack.

5.1.7

BATTERY CHARGE CONTROL

OUTPUT (VBAT1, VBAT2)

The battery charge control output is the drain terminal of

an internal P-channel MOSFET. The MCP7385X

devices provide constant-current and constant-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.

5.2

Digital Circuitry

5.2.1

CHARGE STATUS OUTPUTS

(STAT1,STAT2)

Two status outputs provide information on the state of

charge for the MCP73853. One status output provides

information on the state of charge for the MCP73855.

The current-limited, open-drain outputs can be used to

illuminate external LEDs. Optionally, a pull-up resistor

can be used on the output for communication with a

host microcontroller. Table 5-1 and Table 5-2 summa-

rize the state of the status outputs during a charge

cycle for the MCP73853 and MCP73855, respectively.

The flashing rate (1 Hz) is based off a timer capacitor

(CTIMER) of 0.1 µF. The rate will vary based on the

value of the timer capacitor.

5.2.1.1

MCP73853 Only

STAT2 is on whenever the input voltage is above the

under voltage lockout, the device is enabled, and all

conditions are normal.

During a fault condition, the STAT1 status output will be

off and the STAT2 status output will flash. To recover

from a fault condition, the input voltage must be

removed and then reapplied, or the enable input, EN,

must be de-asserted to a logic-low, then asserted to a

logic-high.

When the voltage on the THERM input is outside the

preset window, the charge cycle will either not start or

be suspended. However, the charge cycle is not termi-

nated, with recovery beng automatic. The charge cycle

will resume (or start) once the THERM input is valid and

all other qualification parameters are met.

5.2.2

VSET INPUT

The VSET input selects the regulated output voltage of

the MCP7385X devices. With VSET tied to VSS, the

MCP7385X devices regulate to 4.1V. With VSET tied to

VDD, the MCP7385X devices regulate to 4.2V.

5.2.3

LOGIC ENABLE (EN)

The logic enable input pin (EN) 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 EN pin, or tying

it to the input source, enables the device. Applying a

logic-low input signal disables the device and termi-

nates a charge cycle. When disabled, the device’s

supply current is reduced to 0.28 µA, typically.

TABLE 5-1:

STATUS OUTPUTS – MCP73853

CHARGE

CYCLE STATE

STAT1

STAT2

Qualification

OFF

Preconditioning

OFF

Constant-

current Fast

Charge

OFF

Constant-

voltage

OFF

Charge

Complete

Flashing (1 Hz,

50% duty cycle)

OFF

Fault

OFF

THERM Invalid

OFF

Flashing (1 Hz,

50% duty cycle)

Disabled -

Sleep mode

OFF

Input Voltage

Disconnected

OFF

Note:

OFF state: open-drain is high-impedance;

ON state: open-drain can sink current,

typically

7 mA;

FLASHING:

toggles

between OFF and ON states.

TABLE 5-2:

STATUS OUTPUT – MCP73855

CHARGE CYCLE STATE

STAT1

Qualification

OFF

Preconditioning

Constant Current Fast Charge

Constant Voltage

Charge Complete

OFF

Fault

Flashing (1Hz,

50% duty cycle)

THERM Invalid

Flashing (1Hz,

50% duty cycle)

Disabled - Sleep mode

OFF

Input Voltage Disconnected

OFF

Note:

OFF state: open-drain is high impedance;

ON state: open-drain can sink current, typ-

ically 7 mA; FLASHING: toggles between

OFF state and ON state.

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