LP3910SQ-AN Datasheet, PDF (40/60 Pages) National Semiconductor (TI) – Power Management IC for Hard Drive Based Portable Media Players

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The current provided by the external adapter power or USB
power, when inserted, first supplies the system load; the re-
mainder is used for charging.
The different paths are configured through two internal power
FETs, Q1 and Q2, and an external Schottky diode. Q1 is a
Power FET that is only active during USB charging. Q2 func-
tions either as a linear Power FET during charging or as a low
R_DSON switch when no external power is present and the bat-
tery discharges to supply power to the system.
Power Route
Regulated adapter supply &
battery charging
USB supply & battery charging
No external supply &
battery discharging
Q1
Q2
OFF Regulated
ON Regulated
OFF ON
The Power Routing function will allocate power to the system
through the V_DD pin and to the battery. V_DD1, V_DD2, V_DD3,
V_IN1, V_IN2, V_IN3, and V_IN4 must be connected together exter-
nally. V_BATT1, V_BATT2, and V_BATT3 must be connected together
externally.
USB SUSPEND MODE
The LP3910SQ-AN USB current consumption can be dis-
abled during suspend mode through a dedicated pin (USB-
SUSP). Applying a logic 1 to this pin will disable the USB
current path and current is reduced to input leakage current
less than 30 µA on the USBPWR pin.
SETTING THE USB CURRENT LIMIT
The USB current that is available from the USB on the VBUS
wire is limited by default to 100 mA. More current (up to
800 mA) can be negotiated through a session request proto-
col between host and peripheral. The USB current limit needs
to be signaled to the LP3910SQ-AN by means of the
USB_ISEL pin or the I_LIMIT Register as indicated below.
If the USB current limit is 100 mA then the USB controller of
the peripheral system needs to set the USB_ISEL logic 0 or by
setting the I_LIMIT register bits [D1, D0] to 2’b00.
If the USB current limit is 500 mA, then the USB controller
needs to apply logic 1 to the USB_ISEL pin or change the I_LIM-
IT ^{register accordingly. Under this condition, the LP3910SQ-}
AN will allow charging with a charge current that is determined
by the Charge Control Register, not exceeding 500 mA.
The LP3910SQ-AN will prevent (through internal circuitry) the
charge current from exceeding the USB current limit, even if
the current setting in the Charge Control Register exceeds
500 mA.
The controller can also select a USB current limit of 800 mA
through I²C that exceeds current USB spec values.
I_LIMIT REGISTER (03)H CURRENT LIMIT REGISTER
Access
Data
D7–2
Read only 0
Reserved
Reset
n/a
D1–0
USB Current Limit
00: controlled by USB_ISEL pin
[low = 100 mA, high = 500 mA]
01: 100 mA
10: 500 mA
11: 800 mA
2’b00
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