JODY-W2 - System integration manual
UBX-18068879 - R14
Design-in
Page 27 of 84
C1 - Public
2.3.1.1
VCC supply circuit design using a switching regulator
It is recommended to use a Switching Mode Power Supply (SMPS) when the difference from the
available supply rail to the
VBAT
rail allows significant power savings. For example, conversion of a
12 V or greater voltage supply to the nominal 3.3 V value for the
VBAT
supply.
The characteristics of the SMPS connected to the
VBAT
pin should meet the following prerequisites
to comply with the module requirements summarized in
•
Power capability:
The switching regulator together with any additional filter in front of the module
must be capable of providing a voltage within the specified operating range. The regulator must
be capable of delivering the specified peak current.
•
Low output ripple
: The switching regulator peak-to-peak Voltage ripple must not exceed the
specified limits. This requirement applies both to voltage ripple generated by SMPS operating
frequency and to high frequency noise generated by power switching.
PWM/PFM mode operation
: It is preferable to select regulators with fixed Pulse Width Modulation
(PWM) mode. Pulse Frequency Modulation (PFM) mode typically exhibits higher ripple and may affect
RF performance. If power consumption is not a concern, PFM/PWM mode transitions should be
avoided in favor of fixed PWM operation to reduce the peak-to-peak noise on voltage rails. Switching
regulators with mixed PWM/PFM mode can be used provided that the PFM/PWM modes and
transition between modes complies with the requirements.
2.3.1.2
Supply circuit design using a Low Drop-Out (LDO) linear regulator
The use of a linear regulator is suggested when the difference from the available supply rail and the
VBAT
or
VIO/1V8
value is relatively low. The linear regulators provide acceptable efficiency when
transforming a supply of less than 5 V to a voltage value within the normal operating range of the
module. A linear regulator can be also considered to power the
VIO/1V8
section due to the low current
requirements, especially if cascaded from a SMPS-generated low voltage rail.
The characteristics of the Low Drop-Out (LDO) linear regulator used to power the voltage rails must
meet the following prerequisites to comply with the requirements summarized in
•
Power capabilities
: The LDO linear regulator with its output circuit must be capable of providing a
voltage value to the
VBAT
or
VIO/1V8
pins within the specified operating range and must be
capable of withstanding and delivering the maximum specified peak current while in connected
mode.
•
Power dissipation
: The power handling capability of the LDO linear regulator must be checked to
limit its junction temperature to the maximum rated operating range. The worst-case junction
temperature can be estimated as shown below:
𝑇
𝑗,𝑒𝑠𝑡
= (𝑉
𝑖𝑛
− 𝑉
𝑜𝑢𝑡
) ∗ 𝐼
𝑎𝑣𝑔
∗ 𝜃
𝑗𝑎
+ 𝑇
𝑎
Where:
𝜃
𝑗𝑎
is the junction-to-
ambient thermal resistance of the LDO’s package
5
,
𝐼
𝑎𝑣𝑔
is the current
consumption of the given voltage rail in continuous TX/RX mode and
𝑇
𝑎
is the maximum operating
temperature of the end product inside the housing.
5
Thermal dissipation capability reported on datasheets is usually tested on a reference board with adequate copper area (ref.
to JESD51). Junction temperature on a typical PCB may be higher than the estimated value due to the limited space to
dissipate the heat. Thermal reliefs on pads also affect the capability of a device to dissipate the heat.
