参数资料
| 型号： | SC824ULTRT |
| 厂商： | Semtech |
| 文件页数： | 25/29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)
Operation Without a Battery
The SC824 can be operated as a 4.2V LDO regulator
without the battery present, for example, for factory
testing. If this use is required, the total output capacitance,
C BAT plus any other capacitors tied directly to BAT pin
network, should be at least 2.2μF but less than 22μF to
ensure stability in CV regulation. To operate the charger
without a battery, the NTC pin should be pulled up to the
VSYS voltage to select No-Battery mode. This can be
accomplished automatically when a battery is absent if
the recommended NTC network is used. See the section
EN_NTC Interface for details.
Capacitor Selection
Low cost, low ESR ceramic capacitors such as the X5R and
X7R dielectric material types are recommended. The BAT
pin capacitor should be at least 1μF, but can be as large as
desired to accommodate the required input capacitors of
regulators connected directly to the battery terminal. BAT
pin total capacitance must be limited if the SC824 is to be
operated without the battery present. See the section
Design Considerations — Large Battery
A battery with a desired fast-charge current exceeding
500mA is most compatible with the USB fixed 1:5 current
ratio low-to-high power model of operation. For example,
consider an 800mAhr battery, with maximum fast-charge
current of 800mA. The adapter input fast-charge should
be configured for 800mA max (R IPRGM = 2.78kΩ equivalent
is required). Select R IPRGM = 4.53kΩ to set USB high power
fast-charge to 450mA, and the USB low power fast-charge
set to 450/5 = 90mA. The MODE pin tri-level logical input
can be used to select between USB high power and USB
low power modes whenever a fixed 5:1 current ratio is
desired. For adapter mode charging, set the MODE pin
high for USB high power mode if UVLR is desired, or low
for adapter mode if current limited adapter capability is
desired. Then switch in a parallel 7.15kΩ IPRGM resistor, as
shown in Figure 7, for an equivalent 2.77kΩ IPRGM resis-
tance. This will program the desired 800mA max adapter
mode fast charge current.
IPRGM
8
Operation Without a Battery. The VIN pin capacitor is typi-
cally between 0.1μF and 2.2μF, although larger values will
not degrade performance. The VSYS pin capacitor must
be at least 1μF. Capacitance must be rated at the expected
Hi/Lo
Current Select
R IPRGM_HI
R IPRGM
bias voltage (4.2V for the BAT pin capacitor, 4.6V for the
VSYS pin capacitor, the expected V VIN supply regulation
voltage for the VIN pin capacitor), rather than the zero-volt
capacitance rating.
PCB Layout Considerations
Layout for linear devices is not as critical as for a switching
regulator. However, careful attention to detail will ensure
reliable operation.
Figure 7 — External Programming of Arbitrary USB
High Power and Low Power Charge Currents
Design Considerations — Small Battery
A battery with a desired fast-charge current less than
500mA will not be charged in the minimum charge time
when in USB low power mode with a 1:5 low-to-high
power mode current ratio. A 300mAhr battery can be
used as an example with maximum fast-charge current of
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Place input and output capacitors close to the
device for optimal transient response and device
behavior.
Connect all ground connections directly to the
ground plane. If there is no ground plane,
connect to a common local ground point before
connecting to board ground near the GND pin.
Attaching the device to a larger copper footprint
will enable better heat transfer from the device
on PCBs with internal ground and power
planes.
300mA. In this example, the adapter input and USB input
high power fast-charge currents should both be set to
300mA. In this case, the fixed USB low-to-high power
charging current ratio of 1:5 would provide a USB low
power mode fast charge current of 60mA.
For this example, setting the USB low power fast-charge
current to 90mA would provide a shorter charge time
without violating USB Vbus current requirements. An
arbitrary ratio of USB low-to-high power charging currents
can be obtained using an external n-channel FET oper-
ated with a processor GPIO signal to engage a second
25
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