User's Manual
Table Of Contents
- GC864 QUAD V2andGC864 DUAL V2Hardware User Guide
- APPLICABILITY TABLE
- 1 Introduction
- 2. Overview
- 3. GC864 Mechanical Dimensions
- 4. GC864-QUAD V2 / GC864-DUAL V2 Module Connections
- 5. Hardware Commands
- 6. Power Supply
- 7. Antenna
- 8. Logic Level Specifications
- 9. Serial Ports
- 10. Audio Section Overview
- 11. General Purpose I/O
- 11.1. GPIO Logic Levels
- 11.2. Using a GPIO Pad as INPUT
- 11.3. Using a GPIO Pad as OUTPUT
- 11.4. Using the RF Transmission Control GPIO4
- 11.5. Using the RFTXMON Output GPIO5
- 11.6. Using the Alarm Output GPIO6
- 11.7. Using the Buzzer Output GPIO7
- 11.8. Magnetic Buzzer Concepts
- 11.9. Using the Temperature Monitor Function
- 11.10. Indication of Network Service Availability
- 11.11. RTC Bypass Out
- 11.12. DAC Converter
- 11.13. ADC Converter
- 12. Assembly the GC864-QUAD V2 / GC864-DUAL V2 on the Board
- 13. Packing System
- 14. Conformity Assessment Issues
GC864 Hardware User Guide
1vv0300874 Rev.0 – 2010-01-25
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved. Page 23 of 64
The GSM system is made in a way that the RF transmission is not continuous but 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, then a strong noise floor is generated on
the ground and the supply; this will reflect on all the audio paths producing an
audible and 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 power supply must be designed so that it is capable of a peak current output of
at least 2 A.
6.2. General Design Rules
The principal guidelines for the Power Supply Design embrace three different design
steps:
• the electrical design
• the thermal design
• the PCB layout.
6.2.1. Electrical Design Guidelines
The electrical design of the power supply depends strongly from the power source
where this power is drained. We will distinguish them into three categories:
• +5V input (typically PC internal regulator output)
• +12V input (typically automotive)
• Battery
6.2.1.1. +5V input Source Power Supply Design Guidelines
• The desired
output for the power supply is 3.8V, hence there is no big
difference between the input source and the desired output. A linear
regulator can be used. A switching power supply will not be suited
because of the low drop out requirements.
• When using a linear regulator, a proper heat sink shall be provided in
order to dissipate the power generated.