TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28
Design-in
Page 75 of 164
2.2.1.5
Guidelines for VCC supply circuit design using a primary battery
The characteristics of a primary (non-rechargeable) battery connected to VCC pins should meet the
following prerequisites to comply with the module VCC requirements summarized in
Maximum pulse and DC discharge current: the non-rechargeable battery with its related output
circuit connected to the VCC pins must be capable of delivering a pulse current as the maximum
peak current consumption during Tx burst at maximum Tx power specified in TOBY-L2 series Data
Sheet
and must be capable of extensively delivering a DC current as the maximum average
current consumption specified in TOBY-L2 series Data Sheet
. The maximum 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 below the operating range summarized in
bursts.
2.2.1.6
Additional guidelines for VCC or 3.3Vaux supply circuit design
To reduce voltage drops, use a low impedance power source. The series resistance of the power supply
lines (connected to the modules’ VCC / 3.3Vaux and GND pins) on the application board and battery
pack should also be considered and minimized: cabling and routing must be as short as possible to
minimize power losses.
Three pins are allocated to VCC supply and five pins to 3.3Vaux supply. Several pins are designated
for GND connection. Even if all the VCC / 3.3Vaux pins and all the GND pins are internally connected
within the module, it is recommended to properly connect all of them to supply the module 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 or 3.3Vaux supply can rise up as specified in TOBY-L2
series Data Sheet
or in MPCI-L2 series Data Sheet
), place a bypass capacitor with large
capacitance (at least 100
µ
F) and low ESR near the VCC pins, for example:
330
µ
F capacitance, 45 m
ESR (e.g. KEMET T520D337M006ATE045, Tantalum Capacitor)
To reduce voltage ripple and noise, improving RF performance especially if the application device
integrates an internal antenna, place the following bypass capacitors near the VCC / 3.3Vaux pins:
68 pF 0402 capacitor with Self-Resonant Frequency in the 800/900 MHz range (e.g. Murata
GRM1555C1H680J) to filter EMI in the RF low frequencies bands
15 pF 0402 capacitor with Self-Resonant Frequency in 1800/1900 MHz range (e.g. Murata
GRM1555C1E150J) to filter EMI in the RF high frequencies bands
8.2 pF 0402 capacitor with Self-Resonant Frequency in 2500/2600 MHz range (e.g. Murata
GRM1555C1H8R2D) to filter EMI in the RF very high frequencies band
10 nF capacitor (e.g. Murata GRM155R71C103K) to filter digital logic noise from clocks and data
sources
100 nF capacitor (e.g. Murata GRM155R61C104K) to filter digital logic noise from clocks and data
sources
A suitable series ferrite bead can be properly placed on the VCC / 3.3Vaux line for additional noise
filtering if required by the specific application according to the whole application board design.
☞
The necessity of each part depends on the specific design, but it is recommended to provide all
the bypass capacitors described in
if the application device integrates an
internal antenna.
