参数资料
| 型号： | SC824ULTRT |
| 厂商： | Semtech |
| 文件页数： | 26/29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)
parallel IPRGM resistor, while selecting high power mode
(MODE pin driven high) for both low or high power USB
charging. The external circuit is similar to that illustrated
in Figure 7.
For USB low power mode charging, the external transistor
is turned off. For adapter mode or USB high power mode,
the external transistor is turned on. The effect of the
switched parallel IPRGM resistor is to reduce the effective
programming resistance and thus raise the fast-charge
current.
A 300mAhr battery with maximum fast-charge current of
300mA is an example. The adapter mode and USB high
power mode fast-charge currents should both be set to
300mA max. The USB input low power fast-charge current
is 100mA max. Refer to the circuit in Figure 7 and the data
of Figures 1a and 1b. For I FQ = 300mA max, R IPRGM = 7.50kΩ
is desired. A fixed IPRGM resistor of R IPRGM = 23.2kΩ pro-
grams I FQ = 100mA max for USB low power charging.
When parallel resistor R IPRGM_HI = 11.0kΩ is switched in, the
equivalent IPRGM resistor is 7.50kΩ, for I FQ = 300mA max.
USB Low Power Mode Alternative
Where a USB mode selection signal is not available, or for
a low capacity battery where system cost or board space
make USB low power mode external current program-
ming impractical, USB low power charging can be sup-
ported indirectly. The IPRGM pin resistance can be
selected to obtain the desired USB high power charge
current. Then, with the MODE pin always configured for
USB high power mode, the UVLR feature will ensure that
the charging load on the VIN pin will never pull the USB
Vbus supply voltage below V UVLR regardless of the host or
hub supply limit. The UVLR limit voltage guarantees that
the voltage of the USB Vbus supply will not be loaded
below the low power voltage specification limit, as seen
by any other low power devices connected to the same
USB host or hub.
Under-voltage load regulation can also be beneficial for
charging small batteries. Instead of switching the pro-
gramming resistor depending on the USB mode, UVLR
(while selecting USB high power mode) can permit charg-
USB Dedicated Charger Compatibility
The SC824 is especially well suited to the USB Charging
Specification, Revision 1.0, Dedicated Charger, Sections
3.5 and 4.1. Important features that support compliance
include low quiescent current when disabled (less than
1.5mA), and selectable current limited supply charging
behavior.
The USB Dedicated Charger is required to limit its output
current to more than 0.5A and less than 1.5A. A dedicated
charger identifies itself by shorting together the USB D+
and D- lines. Once the dedicated charger is detected, the
SC824, with its 1A max programmed fast charge current in
any mode, permits the fast-charge current to be set higher
than the 500mA USB High Power Mode limit to permit
faster charging of a large battery. (See the section Design
Considerations — Large Battery.)
Regardless of the SC824 programmed current, any speci-
fication compliant USB Dedicated Charger will either
supply more than the programmed fast charge current
(and so will regulate to its specified output voltage), or will
limit its output current such that its output voltage will be
pulled down. The USB Dedicated Charger is required to
maintain its current limit down to 2V. By selecting Adapter
Mode, the SC824 input will be pulled down to the battery
voltage plus charging path dropout. This behavior is rec-
ognized in the USB Battery Charging Specification, Section
3.5, as an accepted means to reduce power dissipation in
the device while charging at high current.
If there are additional system circuits requiring that the
USB Vbus node voltage be maintained above the USB Low
Power Mode minimum voltage specification (4.4V), the
SC824 USB High Power Mode should be selected. This
mode enables Under-Voltage Load Regulation, which will
regulate the charging output current, if necessary, to
match the Dedicated Charger current limit while main-
taining V UVLR (nominally 4.51V) at the VIN pin.
Either of these SC824 charging modes will ensure reliable
charging at any programmed charge current, using any
USB Battery Charging Specification compliant Dedicated
Charger, regardless of its current limit.
ing at whatever charge current a USB hub low-power
supply can provide without compromising the integrity of
the hub power supply for other devices.
26
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