ActiveKEY Modem User Manual Page - 4 - of 5
Classification: GE Public
2.4.
SWITCHING POWER SUPPLY
The switching power supply for the ActiveKEY is based on a switchmode buck/boost controller device. For this application
the “SEPIC” mode of operation was chosen for high efficiency operation of the regulator circuitry.
This device is a low noise high speed controller operating at ~800 KHz that is perfectly suited to the ActiveKEY
requirements.
It is capable of regulating the output voltage to 3.6 Volts DC (optimum for the Enfora cellular data modem module) over a
much wider range than can be realized using a Lithium Ion battery.
The actual input range of the power supply is from 1.8 Volts DC to 9.0 Volts DC and it can provide a constant 1 ampere to
a load without issue.
This allows usage in secondary applications with a wide range of available power sources when used as a stand alone
cellular data modem and has plenty of reserve for use by peripheral circuits using the 3.6 Volt output of the switching
regulator.
3.
INTERFACE BOARD
For universal applications of the GE modem card an interface board has been developed to allow the modem card to be
easily utilized in any standard PC type of RS-232 application or direct interface to 3.6 volt logic levels by removal of the on
board level translator (MAX3237) and connection directly to the on board sixteen pin header. A hot air tool is
recommended for removal of the MAX3237 or the interface boards can be supplied without this device and its associated
components mounted on request.
When used in PC type RS-232 applications an external DC supply is required and must be within the 2.5 to 4.5 Volt range
and be capable of supplying up to 2 amperes of peak current. The on board regulator on the modem card will regulate this
input voltage to a precise 3.6 volts to operate the modem circuitry and will supply the MAX3237 level translator IC on the
interface board. The regulated 3.6 Volt supply is available on the sixteen pin header for operating additional external low
current circuitry if desired, up to 200 Ma. is available for this purpose. When used in this mode the sixteen pin header can
be used to monitor the various signals on the RS-232 buss.
When used in the direct mode all connections are made to the on board sixteen pin header, power must be supplied from an
external source and must be in the 2.5 to 4.5 volt range with a capability of supplying up to 2 amperes of peak current.
The on board (modem) voltage regulator will supply external circuitry with the regulated 3.6 volts with a current
requirement up to 200 Ma.
Do not connect the sixteen pin header to external logic with the MAX3237 in place, this may result in damage to both the
MAX3237 and the external logic!
The interface pin out for the sixteen pin header is as follows:
1.
DC input power +2.5 to +4.5 Volts.
2.
Power and logic Ground.
3.
Regulated 3.6 Volts DC output.
4.
Modem Ring signal.
5.
Transmit Data.
6.
Receive Data.
7.
Clear to Send.
8.
Request to Send.
9.
Data Terminal Ready
10.
Data Carrier Detect.