SC824 datasheet(18/29 Pages) SEMTECH

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SC824

Applications Information (continued)

Top-off charging maintains the BAT pin voltage at V

acting as a voltage regulator until the time-out of the top-

off timer. The top-off timer times-out in 45 minutes, at

which time the charger is turned off and enters the

monitor state.

The charge timer is disabled when the RTIME pin is

grounded. In this case, the output is turned off immedi-

ately upon current termination and the charger enters the

monitor state. Note that the pre-charge stage timer will

be active regardless of whether the RTIME pin is grounded,

to detect a grossly defective battery or output short to

ground. A pre-charge timeout will signal a fault and turn

off the charging output.

During the CC timer interval, momentarily grounding (at

least 300μs) and releasing the RTIME pin will reset the CC

mode timer. This feature allows the CC mode timer to be

used as a watchdog timer, enabling the host processor to

extend the CC interval as long as needed for charging a

large battery with a low fast-charge current.

While the charger is in the top-off interval and the timer is

enabled, the RTIME pin can be grounded momentarily (at

least 300μs) to immediately end the charging cycle and

place the charger in the monitor state. In this condition,

the charge timer remains enabled for operation in a sub-

sequent recharge cycle.

An NTC temperature fault will suspend but will not reset

the charge timer, in any timer stage. The timer resumes

from its current state when the battery temperature

returns to the safe-to-charge range.

See the section Logical State Machine for details of timer

stage transitions and sequencing.

Status Outputs

The STAT0 and STAT1 pins are open-drain status indicating

outputs. STAT0 is asserted (driven low) whenever a valid

charging source is present at the VIN input pin. A valid

charging source has a voltage greater than the UVLO

threshold and less than the OVP threshold.

STAT1 is asserted as charging begins and is subsequently

released upon charge termination (by CV stage timeout or

by charge current) to indicate end-of-charge. It is also

released when the charger is disabled and in No-Battery

mode. If the battery is already fully charged when a charge

cycle is initiated, STAT1 is asserted and will remain asserted

for approximately 22 seconds before being released. The

STAT1 pin is not asserted for automatic recharge cycles.

The STAT0 and STAT1 pins may be connected to processor

GPIO ports to notify a host controller of the charging

status, or they can be used as LED drivers. Both are high

voltage inputs, so they can be safely pulled up to the input

100

110

120

130

140

150

160

170

180

190

200

RTIME (k

Ω)

Figure 4b — CC Stage Fault Timeout vs. Programming

Resistance, High Resistance Range

1.75

2.25

2.5

2.75

3.25

3.5

3.75

4.25

4.5

4.75

5.25

5.5

RTIME (k

Ω)

Figure 4a — CC Stage Fault Timeout vs. Programming

Resistance, Low Resistance Range

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