User's Manual

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Note d’étude / Technical document : URDx– OTL 5635.1– 007 / 70 230 Edition 03

Document Sagem Communications Reproduction et divulgation interdites

Sagem Communications document. Reproduction and disclosure prohibited

• The over-discharge problem: most of the Lithium Ion rechargeable batteries are not able to recover their charge when their

voltage reaches a low-level voltage. To avoid this, it is necessary to add a safety component to disconnect the backup

battery in case of over–discharge condition. In such a case, this implementation is too complicated (too much components

for that function).

• The charging current has to be regulated

Sagem communications does not recommend using this kind of backup battery technology.

3.9.4.2 Capacitor battery

These kinds of backup battery have not the drawbacks of the Lithium Ion rechargeable battery.

As there are only capacitors:

• The maximum discharge current is generally bigger,

• There is no problem of over-discharge: the capacitor is able to recover its full charge even if its voltage has

previously fallen to 0V.

• There is no need to regulate the charging current.

Moreover, this kind of battery is available in the same kind of package than the Lithium Ion cell and fully

compatible on a mechanical point of view. The only disadvantage is that the capacity of this kind of battery is

significantly smaller than Manganese Silicon Lithium Ion battery. But for this kind of use (supply internal RTC

when the main battery is removed), the capacity is generally enough.

Sagem communications strongly recommends using this kind of backup battery technology.

3.10 HARDWARE POWER MANAGEMENT AND MULTIPLEXING INTERFACES

In case hardware power management and multiplexing are used, it is necessary to isolate host and HiLo

module in order not to generate current re-injection when HiLo is switched-off.

Typical schematic (only useful signals are represented):

Figure 17: Hardware interface between HiLo and host

In general, solution1 is enough to protect HiLo module.

3.11 STARTING THE MODULE

First power up VBAT, which must be in the range 3.2V – 4.5V, and able to provide 2.2A during the TX bursts

(Refer to the module specification for more details).

To start the module, a low level pulse must be sent on POK_IN during 1 s minimum (at 25°C).

After a few seconds, the module put in active state CTS when it is ready to receive AT commands.

3.12 MODULE SWITCH OFF

AT command “AT*PSCPOF” allows to switch off the module.

DTR, RTS, RXD

DCD, DSR, CTS, TXD, RI

Tri-state command

Buffer

HiLo

Host

Solution

VGPIO