SC805AEVB datasheet(8/17 Pages) SEMTECH

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 2007 Semtech Corp.

SC805A

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POWER MANAGEMENT

General Operation

The SC805A is configured based on the application for fast-

charge and termination current, timing requirements, and

operation with and without a battery (LDO mode). A typical

charging cycle is described below. Details on alternate ap-

plications and output programmability are covered in the

individual sections.

The charging cycle begins when the adapter is plugged in.

The SC805A performs glitch filtering on the VCC input and

initiates a charge cycle when VCC > UVLO. At this time, the

CHRGB signal is active low turning on the charging LED. If

the battery voltage is less than 2.8V, the SC805A will charge

the output with the pre-charge current. When the battery

voltage exceeds 2.8V, the SC805A enters fast-charge or

constant current (CC) mode. When the battery voltage

reaches its final value, the charger enters the constant volt-

age (CV) mode. In this mode the output current decreases

as the battery continues to charge until the termination

current level is reached.

The CHRGB pin goes high when VOUT output current is less

than the programmed termination current, turning off the

‘charging’ LED and turning on the ‘charge complete’ LED.

The SC805A continues to hold the battery in CV charge

mode until the timer expires. At this point the charger

enters the monitor mode where the output remains off

until VOUT drops by 00mV and a new charge cycle is

initiated.

Pre-Charge Mode

Pre-charge mode is automatically enabled whenever the

battery voltage is below 2.8V. It is used to limit the power

dissipation and precondition the battery for fast charging.

The pre-charge current value is selected by the resistor on

the ITERM pin. The pre-charge current is programmable

from 0mA to 25mA. The equation to select the pre-

charge current is given by:

100

1.5

PCI

TERM

If the charge timer is in use there is also a maximum al-

lowed pre-charge duration. If the pre-charge time exceeds

¼ of the total charge cycle, the charger will turn off due to

a pre-charge fault. This fault is cleared when EN or VCC is

toggled or the output voltage rises above 2.8V.

Fast-Charge Mode (CC)

The fast-charge or CC mode is active when the battery volt-

age is above 2.8V and less than the CV or final float charge

voltage of the battery. The fast-charge current can be set to

a maximum of .0A and is selected by the program resistor

on the IPRGM pin. The voltage on this pin will represent

the current through the battery enabling a microprocessor

via an analog-to-digital converter (ADC) to monitor battery

current by sensing the voltage on the IPRGM pin. The equa-

tion to set the fast-charge current is given by:

Note that for a given program resistor the current through

the battery in CV mode can be determined by replacing

.5 with the actual voltage on the IPRGM pin in the above

equation.

The superior fast-charge current accuracy of the SC805A is

obtained by use of US patent 6,836,095 polarity-switched

(i.e., chopped) current sense amplifier to nullify current

measurement offset errors.

Termination Current

Once the battery reaches the program voltage of 4.2V

the device will transition from a constant current source

to a constant voltage source and the current through the

battery begins to decrease while the voltage remains

constant. When the current falls below the programmed

termination current set by the termination resistor on the

ITERM pin, the SC805A will transition the CHRGB pin from

low to high. If the timer is enabled the output will continue

to float charge in CV mode until the timer expires. If the

timer is disabled than the output will turn off as soon as

the termination current level is reached. If the part is in

LDO mode the SC805A will remain on indefinitely at the

regulated CV voltage. The equation to set the termination

current is given by:

100

1.5

ITERM

TERM

Applications Information

1000

1.5

FCI

PRGM

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