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GM862-GPS Hardware User Guide
GM862-GPS HW User Guide
1vv0300728 Rev. 0 - 27/04/06
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 Contents 1 Overview ...........................................................................................................................4 2 Hardware Commands ......................................................................................................5 2.1 Turning ON the GM862-GPS..................................................................................................5 2.2 Turning
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 1 Overview The aim of this document is the description of some hardware solutions useful for developing a product with the Telit GM862-GPS modules. In this document all the basic functions of a mobile phone will be taken into account; for each one of them a proper hardware solution will be suggested and eventually the wrong solutions and common errors to be avoided will be evidenced. Obviously this document can n
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2 Hardware Commands 2.1 Turning ON the GM862-GPS To turn on the GM862-GPS the pin ON# must be tied low for at least 1 second and then released. The maximum current that can be drained from the ON# pin is 0,1 mA. A simple circuit to do it is: ON# R1 Q1 Power ON impulse R2 GND NOTE: don't use any pull up resistor on the ON# line, it is internally pulled up. Using pull up resistor may bring to latch up pr
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 For example: 1- Let's assume you need to drive the ON# pin with a totem pole output of a +3/5 V microcontroller (uP_OUT1): 2- Let's assume you need to drive the ON# pin directly with an ON/OFF button: Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 6 of 55
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2.2 Turning OFF the GM862-GPS The turning off of the device can be done in two ways: • by software command (see GM862-GPS Software User Guide) • by hardware shutdown When the device is shut down by software command or by hardware shutdown, it issues to the network a detach request that informs the network that the device will not be reachable any more. The hardware unconditional shutdown does not issue this
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2.2.2 Hardware Unconditional Reboot To unconditionally Reboot the GM862-GPS the pin RESET# must be tied low for at least 200 milliseconds and then released. The maximum current that can be drained from the ON# pin is 0,15 mA. A simple circuit to do it is: RESET# Unconditional Power OFF impulse GND NOTE: don't use any pull up resistor on the RESET# line nor any to
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 For example: 1- Let's assume you need to drive the RESET# pin with a totem pole output of a +3/5 V microcontroller (uP_OUT2): Unconditional Reboot impulse The hardware unconditional reboot must not be used during normal operation of the device since it does not detach the device from the network. It shall be kept as an emergency exit procedure to be done in the r
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3 Power Supply The power supply circuitry and board layout are the most important part in the full product design and they strongly reflect on the product overall performances, hence read carefully the requirements and the guidelines that will follow for a proper design. 3.1 Power Supply Requirements The GM862-GPS power requirements are: • Nominal Supply Voltage: 3.8 V • Max Supply Voltage: 4.2 V
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2 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. 3.2.1 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 inter
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 An example of linear regulator with 5V input is: Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 12 of 55
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.1.2 + 12V input Source Power Supply Design Guidelines • The desired output for the power supply is 3.8V, hence due to the big difference between the input source and the desired output, a linear regulator is not suited and shall not be used. A switching power supply will be preferable because of its better efficiency especially with the 2A peak current load represented by the GM862-GPS. • When using a sw
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 An example of switching regulator with 12V input is: 3.2.1.3 Battery Source Power Supply Design Guidelines • The desired nominal output for the power supply is 3.8V and the maximum voltage allowed is 4.2V, hence a single 3.7V Li-Ion cell battery type is suited for supplying the power to the Telit GM862-GPS module. The three cells Ni/Cd or Ni/MH 3,6 V Nom. battery types or 4V PB types MUST NOT BE USED since
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.1.4 Battery Charge control Circuitry Design Guidelines The charging process for Li-Ion Batteries can be divided into 4 phases: • Qualification and trickle charging • Fast charge 1 - constant current • Final charge - constant voltage or pulsed charging • Maintenance charge The qualification process consists in a battery voltage measure, indicating roughly its charge status. If the battery is deeply dis
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 As you can see, the charging process is not a trivial task to be done; moreover all these operations should start only if battery temperature is inside a charging range, usually 5°C - 45°C. The GM862-GPS measures the temperature of its internal component, in order to satisfy this last requirement, it's not exactly the same as the battery temperature but in common application the two temperature should not diffe
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.2 Thermal Design Guidelines The thermal design for the power supply heat sink should be done with the following specifications: • Average current consumption during transmission @PWR level max (rms): 500mA • Average current consumption during transmission @ PWR level min (rms): 100mA • Average current during Power Saving: 4mA • Average current during idle (Power Saving disabled) 19mA • Average
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.3 Power Supply PCB layout Guidelines As seen on the electrical design guidelines the power supply shall have a low ESR capacitor on the output to cut the current peaks and a protection diode on the input to protect the supply from spikes and polarity inversion. The placement of these components is crucial for the correct working of the circuitry. A misplaced component can be useless or can even decrease the po
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 4 Serial Ports The serial port on the Telit GM862-GPS is the core of the interface between the module and OEM hardware. 2 serial ports are available on the module: • MODEM SERIAL PORT • GPS SERIAL PORT (NMEA) Several configurations can be designed for the serial port on the OEM hardware, but the most common are: - RS232 PC com port - microcontroller UART @ 2.8V - 3V (Universal Asynchronous Receive Tra
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GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 The signals of the GM862-GPS MODEM serial port are: RS232 Signal GM862-Name Usage Pin GPS Pin Number Number 1 DCD - 36 Data Carrier Detect Output from the GM862-GPS that dcd_uar indicates the carrier presence t 2 RXD - 37 Transmit line *see Note Output transmit line of GM862-GPS tx_uart UART 3 TXD - 20 Receive line *see Note Input receive of the GM862-GPS UART rx_uart 4 DTR - 43 Data Terminal Ready Input
