参数资料
| 型号： | SC811ULTRT |
| 厂商： | Semtech |
| 文件页数： | 17/23页 |
| 文件大小： | 0K |
| 描述： | IC BATTERY MANAGEMENT |
| 标准包装： | 1 |
| 系列： | * |
| 其它名称： | SC811ULDKR |
SC811 / SC813
Applications Information (continued)
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 voltage is greater than the
UVLO level and less than the OVP level of the selected
mode. 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 subsequently 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 will remain asserted for approximately 750μs before
being released. The STATB pin is not asserted for auto-
matic 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 SC811/3 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
simultaneous 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 influ-
ence 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 battery reaches 4.2V and eventually the control-
ler 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
In the SC811/3, 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 by 5% the mode-dependent pro-
grammed fast-charge current, 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 Constant Current, Constant Voltage, “Constant ”
Temperature (CC/CV/CT) 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 SC811/3. The
thermal limiting controller reduces the output current by
i T ≈ 50mA/oC for any junction temperature T J > T TL .
When thermal limiting is inactive,
T J = T A + V Δ I FQ θ JA ,
where V Δ is the voltage difference between the VIN pin
and the BAT pin. However, if T J computed this way exceeds
T TL , then thermal limiting will become active and the
thermal limiting regulation junction temperature will be
T JTL = T A + V Δ I(T JTL ) θ JA ,
where
charge time.
I(T JTL ) = I FQ ? i T (T JTL ? T TL ).
? 2008 Semtech Corporation
17
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| SC813 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Adapter/USB Tri-Mode Single-cell Li-ion Charger |
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