u-blox LEXI-R422, System Integration Manual

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LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 37 of 108
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2.2.1.3 Guidelines for VCC supply circuit design using LDO linear regulator
The use of a linear regulator is suggested when the difference from the available supply rail source
and the
VCC value is low. The linear regulators provide high efficiency when transforming a 5 V DC
supply to a voltage value within the module VCC normal operating range.
The characteristics of the Low Drop-Out (LDO) linear regulator connected to VCC pins should meet
the following prerequisites to comply with the module VCC requirements summarized in Table 6 :
•
Power capabilities : the LDO linear regulator with its output circuit must be capable of providing a
voltage value to the VCC pins within the specified operating range and must be capable of
delivering to VCC pins the maximum current consumption occurring during a transmission at the
maximum Tx power, as specified in the LEXI-R422 data sheet [1] .
• Power dissipation : the power handling capability of the LDO linear regulator must be checked to
limit its junction temperature to the rated range (i.e. check the voltage drop from the maximum
input voltage to the minimum output voltage to evaluate the power dissipation of the regulator).
Figure 19 and the components listed in Table 12 show an example of a high reliability power supply
circuit for LEXI-R422 modules, where the VCC module supply is provided by an LDO linear regulator
capable of delivering the highest peak / pulse current specified for the 2G use-case, with an
appropriate power handling capability. The regulator described in this example supports a wide input
voltage range, and it includes internal circuitry for reverse battery protection, current limiting, thermal
limiting and reverse current protection.
It is recommended to configure the LDO linear regulator to generate a voltage supply value slightly
below the maximum limit of the module
VCC normal operating range (e.g. ~4.1 V). This reduces the
power on the linear regulator and improves the whole thermal design of the supply circuit.
5V
C1
IN OUT
ADJ
GND
1
2 4
5
3
R1
R2
U1
SHDN
LEXI-R422
A13
VCC
A14
VCC
A12 VCC
GND
C2
C3 C4 C5 C6
Figure 19: Example of high reliability VCC supply circuit for LEXI-R422 modules, using an LDO linear regulator
Reference Description Part number - Manufacturer
C1 10 µF capacitor ceramic X5R 0603 20% 6.3 V Generic manufacturer
C2 100 µF capacitor tantalum B_SIZE 20% 6.3V 15m  T520B107M006ATE015 – Kemet
C3 100 nF capacitor ceramic X7R 16 V GRM155R71C104KA01 - Murata
C4 10 nF capacitor ceramic X7R 16 V GRM155R71C103KA01 - Murata
C5 68 pF capacitor ceramic C0G 0402 5% 50 V GRM1555C1E680JA01 - Murata
C6 15 pF capacitor ceramic C0G 0402 5% 50 V GRM1555C1E150JA01 - Murata
R1
9.1 k

resistor 0402 5% 0.1 W
Generic manufacturer
R2 3.9 k  resistor 0402 5% 0.1 W Generic manufacturer
U1 LDO linear regulator ADJ 3.0 A LT1764AEQ#PBF - Linear Technology
Table 12: Suggested components for high reliability VCC circuit for LEXI-R422 modules, using an LDO regulator
☞
See the section 2.2.1.10 , and in particular Figure 26 / Table 18 , for the parts recommended to be
provided if the application device integrates an internal antenna.