MCP73837AMIMF datasheet(16/30 Pages) MICROCHIP

16 / 30 page

MCP73837/8

DS22071A-page 16

4.1

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. The UVLO circuitry has a built-in

hysteresis of 75 mV for the USB-Port and 55 mV for the

AC-Adapter.

In the event a battery is present when the input power

is applied, the input supply must rise 100 mV above the

battery

voltage

before

MCP73837/8

becomes

operational.

The UVLO circuit places the device in shutdown mode

if the input supply falls to within +100 mV of the battery

voltage.

The UVLO circuit is always active. At any time the input

supply is below the UVLO threshold or within +100 mV

of the voltage at the VBAT pin, the MCP73837/8 is

placed in a shutdown mode.

During any UVLO condition, the battery reverse

discharge current shall be less than 2 µA.

4.2

AUTONOMOUS POWER SOURCE

SELECTION

The MCP73837/8 devices are designed to select the

USB-port or the AC-Adapter as the power source

automatically. If the AC-Adapter input is not present,

the USB-Port is selected. If both inputs are available,

the AC-Adapter has first priority.

4.3

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 be con-

nected from PROG1 to VSS. If the PROG1 or PROG2

pin are open or floating, the MCP73837/8 is disabled

and the battery reverse discharge current is less than

2 µA. In this manner, the PROG1 pin acts as a charge

enable and can be used as a manual shutdown.

4.4

Preconditioning

If the voltage at the VBAT pin is less than the

preconditioning threshold, the MCP73837/8 enters a

preconditioning mode. The preconditioning threshold is

factory

set.

Refer

Section 1.0

“Electrical

Characteristics”

for

preconditioning

threshold

options.

In this mode, the MCP73837/8 supplies 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.

When the voltage at the VBAT pin rises above the

preconditioning threshold, the MCP73837/8 enters the

constant current or fast charge mode.

4.5

Constant Current MODE - Fast

Charge

During the constant current mode, the programmed

(AC-Adapter) or selected (USB-Port) charge current is

supplied to the battery or load.

For AC-Adapter, the charge current is established

using a single resistor from PROG to VSS. The

program resistor and the charge current are calculated

using the following equation:

EQUATION 4-1:

where RPROG is in kilo-ohms (kΩ) and IREG is in

milliampers (mA).

When

charging

from

USB-Port,

the

host

microcontroller has the option of selecting either a one

unit load or a five unit loads charge rate based on the

PROG2 input. A logic LOW selects a one unit load

charge rate, a HIGH selects a five unit loads charge

rate, and high impedance input suspends or disables

charging.

Constant current mode is maintained until the voltage

at the VBAT pin reaches the regulation voltage, VREG.,

when constant current mode is invoked, the internal

timer is reset.

4.5.1

TIMER EXPIRED DURING

CONSTANT CURRENT - FAST

CHARGE MODE

If the internal timer expires before the recharge voltage

threshold is reached, a timer fault is indicated and the

charge cycle terminates. The MCP73837/8 remains in

this condition until the battery is removed, the input

battery is removed or the PROG1/2 pin is opened. If the

battery is removed or the PROG1/2 pin is opened, the

MCP73837/8 enters the Stand-by mode where it

remains until a battery is reinserted or the PROG1/2 pin

Note:

If the input power is switched during a

charge cycle, the power path switch-over

shall be a break-before-make connection.

As a result, the charge current can

momentarily go to zero. The charge cycle

timer shall remain continuous.

Note:

USB Specification Rev. 2.0 defines the

maximum absolute current for one unit

load is 100 mA. This value is not an aver-

age over time and shall not be exceed.

REG

1000V

PROG

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

MCP73837AMIMF 数据表(PDF) 16 Page - Microchip Technology

MCP73837AMIMF 数据表(HTML) 16 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

数据表下载