参数资料
| 型号： | SC824ULTRT |
| 厂商： | Semtech |
| 文件页数： | 19/29页 |
| 文件大小： | 0K |
| 描述： | IC BATTERY MANAGEMENT |
| 标准包装： | 1 |
| 系列： | * |
| 其它名称： | SC824ULDKR |
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SC824
Applications Information (continued)
supply to power LEDs. The conditions indicated by STAT0
and STAT1 are summarized in Table 2.
Table 2 — STATx Pin Truth Table
current — to the closed-loop controller. When the output
voltage is suffi ciently 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
Condition
Power applied (VT UVLO < V VIN <
STAT0
0
STAT1
1
battery voltage approaches V CV (nominally 4.2V), the
voltage feedback signal begins to influence the control
loop, which causes the output current to decrease even
VT OVP ), prior to charging
Charging
Charging Done, any stage of a
recharge cycle, or No-Battery
Mode
Charging Fault (Pre-charge or CC
time-out, NTC temperature fault,
IPRGM pin short to ground)
No valid input supply
(asserted) (released)
0 0
(asserted) (asserted)
0 1
(asserted) (released)
1 0
(released) (asserted)
1 1
(released) (released)
though the output voltage has not yet reached V CV . The
output voltage limit dominates the controller when the
battery reaches V CV , 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.
The SC824 uses a logical transition from CC to CV to
recover the charge current lost due to a 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 7mV higher than the CV regu-
The STAT0 and STAT1 outputs indicate charging faults by
asserting STAT1 while releasing STAT0. Charging faults
include pre-charge or CC-stage timeout, a battery NTC
temperature fault (hot or cold), and the shorting of the
IPRGM pin to ground.
Charging status is indicated during precharge, CC charg-
ing, and CV charging until termination. Top-off charging
is not indicated. Upon termination, whether the timer is
enabled or disabled, charging status will be indicated for
an additional 22 seconds, either while top-off charging
with the timer enabled, or while in monitor state with the
output off if the timer is disabled. This feature ensures
that “charging” will be indicated long enough to be seen,
even if the adapter voltage is applied when the battery is
already fully charged. It informs the user that a charge
cycle was begun and completed normally. Note that the
SC824 can terminate charging of a fully charged battery in
as little as a millisecond; without this feature the “charg-
ing” indication would not be visible.
Logical CC-to-CV Transition
The SC824 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
lation voltage, which provides a sharp and clean transition
free of chatter between regulation modes. The difference
between the transition voltage and the regulation voltage
is referred to as the CC/CV overshoot. While in CV regula-
tion, the output current sense remains active. If the output
current exceeds the mode-dependent programmed fast-
charge current by approximately 5%, the controller reverts
to current regulation.
The logical transition from CC to CV results in a faster
charging cycle that is compliant with the specified 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 (TL) is the third output constraint
of the CC/CV/TL control. This feature permits a higher
input OVP threshold in the SC824, and thus the use of
higher regulation voltage or poorly regulated adapters. If
high input voltage results in excessive power dissipation,
the output current is reduced to prevent overheating of
the SC824. The thermal limiting controller reduces the
output current at the rate of i T ≈ ?50mA/oC for any junc-
tion temperature T J > T TL .
19
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