TOBY-R2 series - System integration manual
UBX-16010572 - R10
Design-in
Page 71 of 151
2.2.1.5
Guidelines for VCC supply circuit design using primary (disposable) 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-R2 series data
sheet
and must be capable of extensively delivering a DC current as the maximum average
current consumption specified in TOBY-R2 series data sheet
. The maximum discharge current
is not always reported in the data sheets of batteries, but the max 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 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 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. Several pins are designated for GND connection. It is
recommended to properly connect all of them to supply the module to minimize series resistance
losses.
For modules supporting 2G radio access technology, 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 as specified in the TOBY-R2 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 pins:
68 pF 0402 capacitor with Self-Resonant Frequency in the 800/900 MHz range (e.g. Murata
GRM1555C1H680J)
15 pF 0402 capacitor with Self-Resonant Frequency in the 1800/1900 MHz range (e.g. Murata
GRM1555C1E150J)
10 nF 0402 capacitor (e.g. Murata GRM155R71C103K) to filter digital logic noise from clocks and
data sources
100 nF 0402 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 line for additional noise filtering if
required by the specific application according to the whole application board design.
