LP3925 Datasheet, PDF (31/51 Pages) Texas Instruments – High Performance Power Management Unit for Handset Applications

USB Transceiver
USB TRANSCEIVER
USB transceiver complies with USB 2.0 specification for full-
speed (12Mb/s) device and low-speed (1.5Mb/s) device op-
eration. The transceiver also supports USB Charger Detec-
tion by “Battery Charging Specification Revision 1.0 Mar 8,
2007”. The transceiver includes internal 1.5 kΩ pull-up resis-
tor and it is supplied from USB LDO.
USB transceiver can be configured to 3-pin, 4-pin or 5-pin in-
terface.
If “USB transceiver not used” is configured, then USB
transceiver is disabled in all circumstances, D+ and D- pins
are HiZ and also 1.5 kΩ pull-up resistor is disconnected. USB
LDO has separate enable control and can be used also if
“USB transceiver is not used”.
FIGURE 15. USB Transceiver Block Diagram
30120420
USB Transceiver enable is controlled by register 0x41 (USB
XCVR CONTROL bits) and 0x36 (bit ALLOW USB XCVR IN
SLEEP).
If AUTOMATIC USB DETECTION bit is set 1 then in any cir-
cumstances the USB transceiver stays disabled until USB
Charger Detection is completed. USB Speed is determined
by bit USB SPEED in register 0x4D:
USB SPEED
1 - Full Speed (12 Mb/s)
0 - Low Speed (1.5 Mb/s)
USB CHARGER DETECTION
USB Charger Detection works according to “Battery Charging
Specification Revision 1.0 Mar 8, 2007” published by USB-IF.
To enable USB Charger detection:
(1) bit AUTOMATIC USB DETECTION in register 0x4D
should be set 1; and
(2) Charger should be enabled.
After VIN_CHG voltage was detected to be high enough to
start charging USB Charger Detection waits 900 ms and then
checks D+ and D- for 100 ms. The detection result can be
read form register 0x8D:
31
www.ti.com