Mid-Continent Instruments and Avionics
Revision D, March 21, 2016
Manual Number 9018205
12
SECTION 4 USB CHARGER OPERATION
4.1 DESCRIPTION
The MD93 Dual USB Charging Port converts aircraft DC input voltage within the range specified to a 5V
DC output. This output power is applied to a dual USB-A connector in accordance with the
USB
Implementers Forum
’s
Dedicated Charging Port Compliance Plan.
4.2 OPERATIONAL
MODES
The USB D+ and D- data lines communicate with the USB portable device to tell the device it is a
dedicated charging port (DCP), capable of a higher current than a standard USB port. Each USB port on
the MD93 can provide up to 2.1 amps (simultaneously) at 5 VDC.
4.3 PROTECTIVE
FEATURES
4.3.1 Short Circuit Protection
The MD93 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.
4.3.2 Over-Current
Protection
The MD93 monitors current draw individually on each port. During an over-current condition the
output is turned off until the over-current condition is removed. Once the overcurrent condition is
removed, the unit returns to normal operation.
4.3.3 Low Input Voltage Shutdown
If the input voltage applied to the MD93 drops below 10 VDC the unit will shut down until the applied
voltage returns to a level within operating range.
4.3.4 Over-Temperature
If the temperature of the MD93 becomes elevated, the unit communicates with the USB portable
device to reduce the charge current output to a 1.0 amp limit. When temperature returns to an
acceptable level the unit automatically returns to a higher charge current as required (up to 2.1
amps).
