Rainbow Electronics GM862-GPS - Manual (Page 25)

GM862-GPS Hardware User Guide
1vv0300728 Rev. 8 - 20/09/07
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 25 of 73
In case of GM862-GPS with p/n 3990250689 the GPS consumptions are reduced by a 30% :
GM862-GPS (3 990 250 657) GM862-GPS (3 990 250 689)
Operating current
70 mA ±20%, including 50 mA for the
GPS hardware and 20 mA for the
antenna LNA
55mA, including 35mA GPS for the
GPS hardware and 20 mA for the
antenna LNA
The GSM system is made in a way that the RF transmission is not continuous, else it is packed into
bursts at a base frequency of about 216 Hz, the relative current peaks can be as high as about 2A.
Therefore the power supply has to be designed in order to withstand with these current peaks without
big voltage drops; this means that both the electrical design and the board layout must be designed for
this current flow.
If the layout of the PCB is not well designed a strong noise floor is generated on the ground and the
supply; this will reflect on all the audio paths producing an audible annoying noise at 216 Hz; if the
voltage drop during the peak current absorption is too much, then the device may even shutdown as a
consequence of the supply voltage drop.
TIP: The electrical design for the Power supply should be made ensuring it will be capable of a peak current output
of at least 2 A.