参数资料
| 型号： | SC824ULTRT |
| 厂商： | Semtech |
| 文件页数： | 12/29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
Charger Operation
The SC824 is a single input, tri-mode, stand-alone Li-Ion
battery charger. It has a tri-state MODE input pin that
allows the device to be put in USB high power, USB low
power, or adapter mode. Fast-charge current is pro-
grammed with a resistor from the IPRGM pin to ground.
USB high power mode is equal to adapter mode current.
USB low power current is 20% of fast-charge current.
When a valid input supply is detected, the STAT0 output
goes low. A charge cycle is initiated and the STAT1 output
goes low. When the battery voltage is less than the pre-
charge threshold voltage, the pre-charge current is output
to the battery. Pre-charge current is fixed at 20% of the
programmed adapter mode or USB high power mode
fast-charge current, and is equal to the USB low power
mode fast-charge current.
Fast-charge Constant Current (CC) regulation begins when
the battery voltage exceeds the pre-charge threshold.
The charge current soft-starts in three steps (20%, 60%,
and 100% of programmed fast charge current) to reduce
adapter load transients. In USB low power mode, the CC
current is held at the 20% step.
The charger begins Constant Voltage (CV) regulation
when the battery voltage rises to the fully-charged single-
cell Li-Ion regulation voltage (V CV ), nominally 4.2V. When
regulating the output voltage, the charge current gradu-
ally decreases as the battery charges. The STAT1 output
goes high, after a 20 second delay, when the output
current I BAT drops below the termination current threshold.
This is known as charge termination. The termination
current threshold is 10% of the IPRGM-programmed fast-
charge current regardless of the mode selected.
Each step of the charge cycle is separately timed using the
optional programmable charge timer. Time-out of the
fixed 45 minute pre-charge stage timer or the fixed or
programmable CC stage timer is indicated as a fault, which
is encoded in the STAT0 and STAT1 outputs. Time-out
during the CV timer stage has the same result as normal
charge termination. When the timer is used, the output
remains on for 45 minutes following termination to ensure
that the battery is fully topped-off, then turns off. If the
timer is not used, the charger turns off immediately upon
Optional Top-off Charging, and Monitoring
Depending on the state of the RTIME pin, upon termina-
tion the SC824 either tops-off the battery by operating as
a voltage regulator (known as float charging) for 45
minutes or it immediately turns off its output. Once the
output is turned off, 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. If the timer is
enabled, then the multistage timer also protects the re-
charge cycle. Re-charge cycles are not indicated by the
STAT1 pin.
A forced re-charge cycle can also be periodically com-
manded by the processor to maintain the battery in a
fully charged state without discharging to the re-charge
threshold, and without top-off charging. See the Monitor
State section for details.
Charging Input Mode Dependencies
In adapter mode, a programmed charging current greater
than the adapter’s current limit will pull down the VIN pin
voltage to the battery voltage plus charger dropout
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.
Both USB modes provide Under-Voltage Load Regulation
(UVLR) in which the charging current is reduced if needed
to prevent overloading of the USB Vbus supply. UVLR
ensures the integrity of the USB Vbus supply for all
devices sharing a host or hub supply. UVLR can also serve
as a low-cost alternative to commanding USB low power
charge current where there is no signal available to indi-
cate whether USB low or high power mode should be
selected.
CC Fast-charge Current Programming
CC regulation is active when the battery voltage is above
VT PreQ and less than V CV . When either adapter mode or
USB high power mode is selected, the programmed CC
regulation fast-charge (FQ) current is inversely propor-
tional to the IPRGM pin resistance to GND according to
the following equation:
reaching the termination current.
12
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