SC810 datasheet(14/20 Pages) SEMTECH

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SC810

voltage. ENB should be held low for at least 1ms to ensure

a successful forced re-charge.

Forced re-charge can be requested at any time during the

charge cycle, or even with no charging source present,

with no detrimental effect on charger operation. This

allows the host processor to schedule a forced re-charge

at any desired interval, without regard to whether a charge

cycle is already in progress, or even whether a charging

source is present. Forced re-charge will neither assert nor

release the STATB output.

Status Output

The STATB pin is an open-drain output. It is asserted

(driven low) as charging begins after a valid charging

input is applied and the VIN pin is greater than the input

UVLO level and less than the OVP level. STATB is also

asserted as charging begins after the ENB input returns to

either of the enable voltage ranges (mid or low voltage)

from the disable (high voltage) range. STATB is subse-

quently released when the termination current is reached

to indicate end-of-charge, when the ENB input is driven

high to disable charging, or when the input voltage is

removed. If the battery is already fully charged when a

charge cycle is initiated, STATB is asserted, and remains

asserted for approximately 750μs before being released.

The STATB pin is not asserted for automatic re-charge

cycles.

The STATB pin may be connected to an interrupt input to

notify a host controller of the charging status or it can be

used as an LED driver.

Logical CC-to-CV Transition

The SC810 differs from monolithic linear single cell Li-ion

chargers that implement a linear transition from CC to CV

regulation. The linear transition method uses two simul-

taneous feedback signals — output voltage and output

current — to the closed-loop controller. When the output

voltage is sufficiently below the CV regulation voltage, the

influence of the voltage feedback is negligible and the

output current is regulated to the desired current. As the

battery voltage approaches the CV regulation voltage

(4.2V), the voltage feedback signal begins to influence the

control loop, which causes the output current to decrease

although the output voltage has not reached 4.2V. The

output voltage limit dominates the controller when the

Applications Information (continued)

battery reaches 4.2V and eventually the controller is

entirely in CV regulation. The soft transition effectively

reduces the charge current below that which is permitted

for a portion of the charge cycle, which increases charge

time.

In the SC810, a logical transition is implemented from CC

to CV to recover the charge current lost due to the soft

transition. The controller regulates only current until the

output voltage exceeds the transition threshold voltage.

It then switches to CV regulation. The transition voltage

from CC to CV regulation is typically 5mV higher than the

CV regulation voltage, which provides a sharp and clean

transition free of chatter between regulation modes. The

difference between the transition voltage and the regula-

tion voltage is termed the CC/CV overshoot. While in CV

regulation, the output current sense remains active. If the

output current exceeds the programmed fast-charge

current by 5%, the controller reverts to current

regulation.

The logical transition from CC to CV results in the fastest

possible charging cycle that is compliant with the speci-

fied current and voltage limits of the Li-ion cell. The output

current is constant at the CC limit, then decreases abruptly

when the output voltage steps from the overshoot voltage

to the regulation voltage at the transition to CV control.

Thermal Limiting

Device thermal limiting is the third output constraint of

the CC/CV/TL control. This feature permits a higher input

OVP threshold, and thus the use of higher voltage or

poorly regulated adapters. If high input voltage results in

excessive power dissipation, the output current is reduced

to prevent overheating of the SC810. The thermal limiting

controller reduces the output current by i

≈ –50mA/ºC for

any junction temperature T

> T

When thermal limiting is inactive,

= T

+ V

where V

is the voltage difference between the VIN pin

and the BAT pin. However, if T

computed this way exceeds

, then thermal limiting will become active and the

thermal limiting regulation junction temperature will be

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