Rainbow Electronics MG260 - Manual (Page 32)

MG260 Product Specification
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Uripp
– 2 RX / 1 TX),
e Max current 2/8 of the time (around 1154 µs every 4.615 ms for GSM/GPRS class
10 – 3 RX / 2 TX).
Because VBATT supplies directly the GSM RF power amplifier component, it is essential to
keep a minimum voltage ripple at this connection in order to avoid any phase error or
spectrum modulation degradation. See paragraph 2.9 Electrical characteristics for
detailed information.
Refer to document [2] for further information about power supply design.
Vmax
VBATT
Uripp
Vmin
IBATT
T=577µs
T = 4.615ms
Legend:
In GSM or GPRS class 2 modes
In GPRS class 10 mode
Figure 8: Typical power supply voltage in GSM/GPRS mode
2.5.1.2 RTC back-up power supply
If using the MG260 internal Real Time Clock (RTC), it is necessary to provide a back-up
power supply because:
When the MG260 module is powered on, the RTC power supply is provided by the module.
When the MG260 module is powered off, a back-up power supply is needed to save RTC
date and time information for GSM part and to save Backup RAM with RTC data, valid
almanac and ephemeredes to perform a Hot start or a War mstart for GPS part (The GPS
will perform a FIX faster).
Nevertheless, since it is possible to retrieve GPS time and date information, it is not
necessary to use this backup power supply interface.
If the RTC is not used, this pin can be left open.
Note: Only after GPS have been supplied, the RTC section and the back-up battery switch
will be initialized properly. If only VCC_RTC is applied first, the current consumption of the
RTC and back up SRAM is undetermined.