ThingMagic Mercury xPRESS Platform v1.7 - Manual (Page 122)

A D I V I S I O N O F T R I M B L E
122 Hardware Reference Guide
but does not have the capacity to supply enough power to the Micro when it transmits. It
cannot be used to power the M6e because, internally, the power from this interface is not
kept at 5 V, which is what the M6e requires.
If an Li-ion battery is present and the USB port is the only source of external power, the
internal system voltage will be the same ideal voltage used to power the battery. This
voltage can be as low as 3.6 V for a discharged battery and as high as 4.2 V for a fully
charged battery (while charging, the system voltage is the battery voltage plus 0.3 Volts).
If no battery is present, the system voltage will be 4.2 V.
The system will also supply power to a client USB port if running on battery power. As the
battery voltage goes down, the limit of the amount current the system will supply before it
detects an over-current condition is reduced. At the low battery voltage of 3.5 V, the
threshold is around 1.1 A.
The power state of the USB interface does not affect its ability to send and receive data.
Li-ion Battery
The xPRESS motherboard is designed to support applications where the reader is
connected to an AC adapter or USB host to charge a battery, then is disconnected from
these power sources and powered by the battery alone.
The system uses a very sophisticated battery charger, the LTC4098 (U5) which is only
compatible with Li-ion batteries.
As noted above, the system will run from the battery whenever the AC adapter level (or
POE input level) drops below 4.3 V, even if a USB connection is present. The USB
interface will charge the battery during periods of inactivity, using the 500 mA it has
available, but the battery power will be used whenever the module is actively reading and
current levels above this are required. Switching back and forth between these states is
governed by whether the battery voltage or the charging voltage out of the Battery
Charging Controller is higher.
Comm Bus (“POE”) Power
The system may be powered by Comm Port pins 47-51 (used in parallel to provide higher
current capacity). This power input is identified as “POE”, or “Power Over Ethernet”, but it
is required that this power will be regulated down to 5V before it reaches the xPRESS
motherboard. The system cannot tolerate the nominal 48V that is obtained directly from
an Ethernet interface. (The labeling is in anticipation that ThingMagic will offer an
Ethernet interface board that does the required voltage regulation.)
Jumper J12 controls whether system power is supplied from the Comm Bus interface (5V,
“POE”) or other sources (AC, Battery or USB). When system power is sourced from the