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D027173_07 CR821X Dual Board Decoded Scan Engine Integration Guide
The development board provides current shunt amplifiers for two different
ranges to perform power measurements on the engine. Switch S2 will
select which path the current to the engine is routed.
The center position of S2 has no shunt, and directly connects VDEV (the
voltage selected by S1, 3.3V or 5V) to VOUT (the voltage to the engine
provided through J2).
Using an oscilloscope capable of math functions, such as the Keysight
InfiniiVision MSOX3104T, and two voltage probes, the engine’s power can
be easily measured in the operating and sleep states. Measure VOUT and
multiply with the calculated current to get power.
Operating Current
The left position of S2, closest to the engine, has a 2mΩ shunt between
VDEV and VOUT. The shunt has an integrated current shunt amplifier
that provides a factory calibrated gain of 2.0V/A. The voltage output of
this amplifier can be read from VHI on TP14 or TP15. To convert from
the voltage output to a current, divide the output by 2. This amplifier is
capable of measuring up to 500mA with a max VHI of 5V.
Sleep Current
To measure the current when the engine is asleep, first the offset of
the system needs to be measured. Disconnect the engine from the
development board by disconnecting the ribbon cable from J2. Turn on
the development board, set the desired voltage on S1, then set S2 in the
rightmost position closest to the RJ50 connector. Use a multimeter or
oscilloscope to measure the VLOW voltage on TP16 or TP17. This voltage
is the offset of the measurement.
To perform a sleep current measurement, start with S2 in either the left
or center position. Wait until the engine sleeps or put it to sleep. LED0
will be off if the engine is asleep and on if it is awake. When the engine
is asleep, move S2 to the right position closest to the RJ50 and USB
connectors. This will route the current to the engine through a 10Ω shunt
attached to a current shunt amplifier with a gain of 100V/V. The output
of the amplifier can be read from VLOW on TP16 or TP17. To convert
from voltage to current, subtract the offset you measured earlier from
VLOW and divide by 1000. The silkscreen on Rev 01 PCB’s does not
show the correct formula or range. The max range for the low current path
measurement is 5mA with a max VLOW of 5V.
9.3 – Power Measurements
