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LISA-U series - System Integration Manual

UBX-13001118 - R17

Advance information

System description

Page 80 of 190

1.9.3.2

USB and power saving

The modules automatically enter the USB suspended state when the device has observed no bus traffic for a
specific time period according to the

USB 2.0 specification

[8]. In suspended state, the module maintains any

USB internal status as device. In addition, the module enters the suspended state when the hub port it is
attached to is disabled. This is referred to as USB selective suspend.
If the USB is suspended and a power saving configuration is enabled by the AT+UPSV command, the module
automatically enters the low power idle-mode whenever possible but it wakes up to active-mode according to
any required activity related to the network (e.g. the periodic paging reception described in section 1.5.3.3) or
any other required activity related to the functions / interfaces of the module.
The USB exits suspend mode when there is bus activity. If the USB is connected and not suspended, the module
is forced to stay in active-mode, therefore the AT+UPSV settings are overruled but they have effect on the power
saving configuration of the other interfaces.
The modules are capable of USB remote wake-up signaling: i.e. it may request the host to exit suspend mode or
selective suspend by using electrical signaling to indicate remote wake-up, for example due to incoming call,
URCs, data reception on a socket. The remote wake-up signaling notifies the host that it should resume from its
suspended mode, if necessary, and service the external event. Remote wake-up is accomplished using electrical
signaling described in the

USB 2.0 specifications

[8].

For the module current consumption description with power saving enabled and USB suspended, or with power
saving disabled and USB not suspended, see the sections 1.5.3.3 and 1.5.3.4 and

LISA-U1 series Data Sheet

[1]

or the

LISA-U2 series Data Sheet

[2].

1.9.3.3

USB application circuit

Since the module acts as a USB device, the USB supply (5.0 V typ.) must be provided to

VUSB_DET

by the

connected USB host. The USB interface is enabled only when a valid voltage as USB supply is detected by the

VUSB_DET

input. Neither the USB interface, nor the whole module is supplied by the

VUSB_DET

input: the

VUSB_DET

senses the USB supply voltage and absorbs few microamperes.

The

USB_D+

and

USB_D-

lines carry the USB serial data and signaling. The lines are used in single ended mode

for relatively low speed signaling handshake, as well as in differential mode for fast signaling and data transfer.
USB pull-up or pull-down resistors on pins

USB_D+

and

USB_D-

as required by the

Universal Serial Bus Revision

2.0 specification

[8] are part of the USB pad driver and do not need to be externally provided.

External series resistors on pins

USB_D+

and

USB_D-

as required by the