MCP73123 datasheet(17/34 Pages) MICROCHIP

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DS22191A-page 17

MCP73123/223

5.0

DETAILED DESCRIPTION

5.1

Undervoltage Lockout (UVLO)

An internal undervoltage lockout (UVLO) circuit

monitors the input voltage and keeps the charger in

shutdown mode until the input supply rises above the

UVLO threshold. In the event a battery is present when

the input power is applied, the input supply must rise

approximately 150 mV above the battery voltage

before the MCP73123/223 device become operational.

The UVLO circuit places the device in shutdown mode

if the input supply falls to approximately 150 mV above

the battery voltage.The UVLO circuit is always active.

At any time, the input supply is below the UVLO

threshold or approximately 150 mV of the voltage at the

VBAT pin, the MCP73123/223 device is placed in a

shutdown mode.

5.2

Overvoltage Protection (OVP)

An internal overvoltage protection (OVP) circuit

monitors the input voltage and keeps the charger in

shutdown mode when the input supply rises above

the OVP

threshold.

The

hysteresis

OVP

approximately 150 mV for the MCP73123/223 device.

The MCP73123/223 device is operational between

UVLO and OVP threshold. The OVP circuit is also

recognized as overvoltage lock out (OVLO).

5.3

Charge Qualification

When the input power is applied, the input supply must

rise 150 mV above the battery voltage before the

MCP73123/223 becomes operational.

The automatic power down circuit places the device in

a shutdown mode if the input supply falls to within

+50 mV of the battery voltage.

The automatic circuit is always active. At any time the

input supply is within +50 mV of the voltage at the

VBAT pin, the MCP73123/223 is placed in a shutdown

mode.

For a charge cycle to begin, the automatic power

down conditions must be met and the charge enable

input must be above the input high threshold.

5.3.1

BATTERY MANAGEMENT INPUT

SUPPLY (VDD)

The VDD input is the input supply to the MCP73123/

223.

The MCP73123/223

automatically

enters

Power-down mode if the voltage on the VDD input falls

to within +50 mV of the battery voltage. This feature

prevents draining the battery pack when the VDD

supply is not present.

5.3.2

BATTERY CHARGE CONTROL

OUTPUT (VBAT)

The battery charge control output is the drain terminal

of an internal P-channel MOSFET. The MCP73123/223

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.

5.3.3

BATTERY DETECTION

The MCP73123/223 detects the battery presence with

charging of the output capacitor. The charge flow will

initiate when the voltage on VBAT is pulled below the

VRECHARGE

threshold.

Refer

Section 1.0

“Electrical Characteristics” for V

RECHARGE values.

The value will be the same for non-rechargeable

device.

When VBAT > VREG + Hysteresis, the charge will be

suspended or not start, depends on the condition to

prevent over charge that may occur.

5.4

Preconditioning

If the voltage at the VBAT pin is less than the

preconditioning threshold, the MCP73123/223 device

enters a preconditioning mode. The preconditioning

threshold

factory

set.

Refer

Section 1.0

“Electrical

Characteristics”

for

preconditioning

threshold options.

In this mode, the MCP73123/223 device supplies 10%

of the fast charge current (established with the value of

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

When the voltage at the VBAT pin rises above the

preconditioning threshold, the MCP73123/223 device

enters the constant current (fast charge) mode.

5.4.1

TIMER EXPIRED DURING

PRECONDITIONING MODE

If the internal timer expires before the voltage threshold

is reached for fast charge mode, a timer fault is

indicated and the charge cycle terminates. The

MCP73123/223 device remains in this condition until

the battery is removed or input power is cycled. If the

battery is removed, the MCP73123/223 device enters

the Stand-by mode where it remains until a battery is

reinserted.

Note:

In order to extend the battery cycle life, the

charge will initiate only when battery

voltage is below 3.4V per cell.

Note:

The MCP73123/223 also offer options

with no preconditioning.

Note:

The

typical

preconditioning

timer

for

MCP73123/223

minutes.

The

MCP73123/223 also offer options with no

preconditioning timer.

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