MC75i Hardware Interface Description
7 Sample Application
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MC75i_HD_v01.100a
Page 109 of 122
2009-08-13
Confidential / Released
7
Sample Application
shows a typical example of how to integrate a MC75i module into the GSM part of a
mobile application. Usage of the various host interfaces depends on the desired features of the
application.
Audio interface 1 demonstrates the balanced connection of microphone and earpiece. This so-
lution is particularly well suited for internal transducers. Audio interface 2 uses an unbalanced
microphone and earpiece connection typically found in headset applications.
The charging circuit is optimized for the charging stages (trickle charging and software con-
trolled charging) as well as the battery and charger specifications described in
.
The PWR_IND line is an open collector that needs an external pull-up resistor which connects
to the voltage supply VCC µC of the microcontroller. Low state of the open collector pulls the
PWR_IND signal low and indicates that the MC75i module is active, high level notifies the Pow-
er-down mode.
If the module is in Power-down mode avoid current flowing from any other source into the mod-
ule circuit, for example reverse current from high state external control lines. Therefore, the
controlling application must be designed to prevent reverse flow. This is not necessary for the
USB interface.
If the I2C bus is active the two lines I2CCLK and I2DAT are locked for use as SPI lines. Vice
versa, the activation of the SPI locks both lines for I2C. Settings for either interface are made
by using the AT^SSPI command.
The internal pull-up resistors (Rp) of the I2C interface can be connected to an external power
supply or to the VEXT line of MC75i. The advantage of using VEXT is that when the module
enters the Power-down mode, the I2CI interface is shut down as well. If you prefer to connect
the resistors to an external power supply, take care that the interface is shut down when the
PWR_IND signal goes high in Power-down mode.
The EMC measures are best practice recommendations. In fact, an adequate EMC strategy for
an individual application is very much determined by the overall layout and, especially, the po-
sition of components. For example, mounting the internal acoustic transducers directly on the
PCB eliminates the need to use the ferrite beads shown in the sample schematic. However,
when connecting cables to the module’s interfaces it is strongly recommended to add appro-
priate ferrite beads for reducing RF radiation.
Disclaimer
No warranty, either stated or implied, is provided on the sample schematic diagram shown in
and the information detailed in this section. As functionality and compliance with na-
tional regulations depend to a great amount on the used electronic components and the indi-
vidual application layout manufacturers are required to ensure adequate design and operating
safeguards for their products using MC75i modules.
