Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 25 of 182
Rechargeable Li-Ion or Li-Pol battery
Rechargeable Li-Ion or Li-Pol batteries connected to the VCC pins should meet the following
requirements:
 Maximum pulse and DC discharge current: the rechargeable Li-Ion battery with its output circuit
must be capable of delivering 2.5 A current pulses with 1/8 duty-cycle to the VCC pins and must
be capable of delivering a DC current greater than the module’s maximum average current
consumption to VCC pins. The maximum pulse discharge current and the maximum DC discharge
current are not always reported in battery data sheets, but the maximum DC discharge current is
typically almost equal to the battery capacity in Amp-hours divided by 1 hour.
 DC series resistance: the rechargeable Li-Ion battery with its output circuit must be capable of
avoiding a VCC voltage drop greater than 400 mV during transmit bursts.
Primary (disposable) battery
The characteristics of a primary (non-rechargeable) battery connected to VCC pins should meet the
following requirements:
 Maximum pulse and DC discharge current: the non-rechargeable battery with its output circuit
must be capable of delivering 2.5 A current pulses with 1/8 duty-cycle to the VCC pins and must
be capable of delivering a DC current greater than the module maximum average current
consumption at the VCC pins. The maximum pulse and the maximum DC discharge current is not
always reported in battery data sheets, but the maximum DC discharge current is typically almost
equal to the battery capacity in Amp-hours divided by 1 hour.
 DC series resistance: the non-rechargeable battery with its output circuit must be capable of
avoiding a VCC voltage drop greater than 400 mV during transmit bursts.
Additional recommendations for the VCC supply application circuits
To reduce voltage drops, use a low impedance power source. The resistance of the power supply lines
(connected to the VCC and GND pins of the module) on the application board and battery pack should
also be considered and minimized: cabling and routing must be as short as possible in order to
minimize power losses.
It is recommended to properly connect all three VCC pins and all twenty GND pins of the module to
the supply source to minimize series resistance losses.
To avoid voltage drop undershoot and overshoot at the start and end of a transmit burst during a GSM
call (when current consumption on the VCC supply can rise up to as much as 2.5 A in the worst case),
place a bypass capacitor with large capacitance (more than 100 µ F) and low ESR near the VCC pins,
for example:
 330 µ F capacitance, 45 mΩ ESR (e.g. KEMET T520D337M006ATE045, Tantalum Capacitor)
The use of very large capacitors (i.e. greater than 1000 µ F) on the VCC line and the use of the soft
start function provided by some voltage regulators must be carefully evaluated, since the voltage at
the VCC pins must ramp from 2.5 V to 3.2 V within 1 ms to allow a proper switch-on of the module.
To reduce voltage ripple and noise, which should improve RF performance if the application device
integrates an internal antenna, place the following series ferrite bead and bypass capacitors near the
VCC pins of the module:
 Ferrite bead for GHz band noise (e.g. Murata BLM18EG221SN1) as close as possible to the VCC
pins of the module, implementing the circuit described in Figure 9, to filter EMI in all the GSM /
UMTS bands.