Manual Number 9018205 Revision F, April 1, 2021
14
SECTION 4 OPERATION
4.1 UNIT ARCHITECTURE
The CH93 is comprised of two functional building blocks, a USB charger and digital clock. The DC
input voltage is regulated over its specified range using a DC-DC converter to power the USB
charger and all clock functions. A charging port controller manages power output for the USB
charging ports. An internal battery maintains clock functions (local time, universal time, flight timer)
when input power is removed for up to ten years. Type 1 units require factory serviced to be
replaced and Type 2 units have a field-replaceable battery. Refer to Section 5.1 for details.
The user interface is comprised of the display, three control buttons, and the mode annunciation.
The display has six, seven-segment, white LED digits that are 0.360” tall and 0.138” wide. The
three user interface buttons (
MODE
,
–
and
+
) are used to switch between modes of operation, set
clock time, and manage timer functions for the CH93. Backlit annunciations on the front bezel
indicate the current mode of operation with each mode visible only when active. When aircraft
power is removed, the display clock and all annunciations will be turned off.
4.2 CLOCK AND USB PROTECTIVE FEATURES
The following features are included in the design of the CH93 and protect both the unit and any
devices being charged from damage in the event of the fault conditions listed below.
Short Circuit Protection
The CH93 is capable of surviving a short circuit event without permanent damage. The unit
enters an over-current condition so that the average current is significantly reduced and the
device is protected. Removal of the short allows the unit to return to normal operation.
Over-Current Protection
The CH93 monitors current draw individually on each USB port. During an over-current
condition the voltage is reduced. If the voltage falls below 3.8 VDC the output is turned off for
a period of 12 seconds. The output is then checked for continued over-current conditions
every 16 milliseconds. This condition is referred to as a hiccup mode. The device stays in this
mode until the over-current condition is removed, then returns to normal operation.
Low Input Voltage Shutdown
If the input voltage applied to the CH93 drops below the specified minimum, the unit will shut
down until the applied voltage returns to a level within the operating range.
Over-Temperature
If the temperature of the CH93 exceeds designed thresholds due to a fault or excessive load,
the unit communicates with the USB portable device to reduce the charge current output to a
1.0 amp limit. This allows the charger to continue charging while the unit returns to a
temperature within designed limits. When temperature returns to an acceptable level the unit
automatically returns to normal operation.
