UR7HCTS2-P840 Datasheet, PDF (5/16 Pages) Semtech Corporation – High-Performance, Low Power PS/2 Touch Screen Controller/Digitizer

POWER MANAGEMENT (CON’T)
The "Stop" mode is the lowest
power consumption mode. In this
mode, the oscillator is stopped and
the IC consumes only the leakage
current. This is the default mode to
which the IC will revert when it is
idle. An event or signal conditions
wake-up the IC. The
ScreenCoder^TM PS2 can still
operate most of the time at only
1uA, even when the host is in the
active state, and with active
external PS/2 device attached to
the ScreenCoder^TM PS2. If an
external PS/2 device sends a data
packet, the ScreenCoder^TM PS2 will
exit the "Stop" mode for as long as
it takes to process the message
and relay the information to the
system. This operation is done
transparently to the host, without
any data loss or any response
delay from the input device.
System-coordinated Power
Management
Normal Operation State
In normal operation state, both
_PWR_DOWN and XPWRS pins are
in high state. ScreenCoder^TM PS2
operations are controlled by Self-
Power Management^TM.
Critical Suspend
At any time, the Host may negate
the _PWR_DOWN pin in order to
force the ScreenCoder^TM PS2 into a
"Critical suspend" mode. This
signal can be activated (driven
low) due to specific conditions of
the Host's operations (for example,
a discharged battery), or due to
actions of the Operating System or
BIOS.
Figure 1: Semtech’s Self-Power Management^TM State
System Request To Send,
Mouse hot plug or Data Packet,
Touch Screen activity,
Button press
RUN
STOP
1s of inactivity
POWER MANAGEMENT (CON’T)
During the "Critical suspend", the ScreenCoder^TM will shut down all of the
pointing activities. However, the communications with the Host are still
enabled.
External PS/2 power down
The ScreenCoder^TM PS2 monitors the power state of the external PS/2
pointing device through the XPWRS pin. If the IC senses that the external
PS/2 device has been powered-down by the host, it will actively eliminate
shot-through current in the input buffers for the clock and data lines by
driving both low.
The ScreenCoder^TM UR7HCTS2-P840 will re-initialize the external PS/2
pointing device when the power to the external PS/2 port is restored.
Figure 2: Semtech’s System-coordinated Power Management
Critical Suspend
_PWR_DOWN=0
_PWR_DOWN=1
and XPWRS=0
_PWR_DOWN=0
_PWR_DOWN=1
and XPWRS=1
Ext Mouse
power down
_PWR_DOWN=1
and XPWRS=0
_PWR_DOWN=1
and XPWRS=1
Normal State
Copyright ©1999-2001 Semtech Corporation
5
DOC7-TS2-P840-DS-106
www.semtech.com