SC810 datasheet(10/20 Pages) SEMTECH

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SC810

Charger Operation

The SC810 is a single cell Li-ion battery charger. It imple-

ments a Constant Current (CC), Constant Voltage (CV)

charging algorithm with Thermal Limiting (TL).

When a valid input supply is first detected, a charge cycle

is initiated and the STATB open-drain output goes low. If

the battery voltage is less than the pre-charge threshold

voltage, the pre-charge current is supplied. Pre-charge

current is 20% of the programmed fast-charge current.

When the battery voltage exceeds the pre-charge thresh-

old, typically within seconds for a standard battery with a

starting cell voltage greater than 2V, the fast-charge CC

mode begins. The charge current soft-starts in three steps

(20%, 60%, and 100% of programmed fast-charge current)

to reduce adapter load transients. CC current is pro-

grammed by the IPRGM resistance to ground.

The charger begins CV regulation when the battery

voltage rises to the fully-charged single-cell Li-ion regula-

tion voltage (V

), nominally 4.2V. In CV regulation, the

output voltage is regulated, and as the battery charges,

the charge current gradually decreases. The STATB output

goes high when I

BAT

drops below the termination thresh-

old current, which is 10% of the IPRGM pin programmed

fast-charge current. This is known as charge termination.

Optional Float-charging or Monitoring

Depending on the state of the ENB input, upon termina-

tion, the SC810 either operates indefinitely as a voltage

regulator (float-charging) or it turns off its output. If the

output is turned off upon termination, the device enters

the monitor state. In this state, the output remains off

until the BAT pin voltage decreases by the re-charge

threshold (VT

ReQ = 100mV typically).

A re-charge cycle

then begins automatically and the process repeats. A

forced re-charge cycle can also be periodically com-

manded by the processor to keep the battery topped-off

without float-charging. See the Monitor State section for

details. Re-charge cycles are not indicated by the STATB

pin.

Charging Input Pin Properties

Glitch filtering is performed on the VIN pin, so an input

voltage that is ringing across its Under-Voltage Lockout

(UVLO) threshold will not be recognized until the ringing

has ceased. The UVLO rising threshold is set higher than

the voltage of a fully charged Li-ion single cell battery,

ensuring that only a charging source capable of fully

charging the battery has been applied. If the charging

current loads the adapter beyond its current limit, the

input voltage will be pulled down to just above the

battery voltage. This is referred to as Current-Limited-

Adapter (CLA) operation. The UVLO falling threshold is

set close to the battery voltage pre-charge threshold to

permit low-dissipation charging from a current limited

adapter.

Constant Current Mode Fast-charge Current

Programming

The CC mode is active when the battery voltage is above

PreQ and less than VCV. The programmed CC regulation

fast-charge (FQ) current is inversely proportional to the

resistance between IPRGM and GND according to the

equation

1000

IPRGM

Typ

IPRGM

The fast-charge current can be programmed for a

minimum of 70mA (R

IPRGM

= 29.4kΩ) and a maximum of

995mA (R

IPRGM

= 2.05kΩ), nominally.

Current regulation accuracy is dominated by gain error at

high current settings, and offset error at low current set-

tings. The range of expected fast-charge output current

versus programming resistance is shown in Figures 1a

and 1b. The figures show the nominal current versus

nominal R

IPRGM

resistance as the center plot and two theo-

retical limit plots indicating maximum and minimum

current versus nominal programming resistance. These

plots are derived from models of the expected worst-case

contribution of error sources depending on programmed

current. The current range includes the uncertainty due

to 1% tolerance resistors. The dots on each plot indicate

the currents obtained with the Electronic Industries

Association (EIA) E96 standard value 1% tolerance resis-

tors. Figures 1a and 1b show low and high resistance

ranges, respectively.

Applications Information

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