User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual

UBX-13000995 - R18 Advance Information Design-in

Page 95 of 206

x Output voltage slope: the use of the soft start function provided by some voltage regulator should be

carefully evaluated, since the VCC pins voltage must ramp from 2.5 V to 3.2 V in less than 1 ms to switch on

the SARA-U2 modules or in less than 4 ms to switch on the SARA-G3 modules by applying VCC supply, that

otherwise can be switched on by forcing a low level on the RESET_N pin during the VCC rising edge and

then releasing the RESET_N pin when the VCC supply voltage stabilizes at its proper nominal value.

Figure 42 and the components listed in Table 25 show an example of a high reliability power supply circuit,

where the VCC module supply is provided by an LDO linear regulator capable of delivering the specified highest

peak / pulse current, with proper 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 as in the circuit described in Figure 42

and Table 25). This reduces the power on the linear regulator and improves the whole thermal design of the

supply circuit.

IN OUT

ADJ

GND

C2R1

SHDN

SARA-G3 / SARA-U2

VCC

GND

Figure 42: Suggested schematic design for the VCC voltage supply application circuit using an LDO linear regulator

Reference Description Part Number - Manufacturer

C1, C2

10 μF Capacitor Ceramic X5R 0603 20% 6.3 V

GRM188R60J106ME47 - Murata

9.1 k: Resistor 0402 5% 0.1 W

RC0402JR-079K1L - Yageo Phycomp

3.9 k: Resistor 0402 5% 0.1 W

RC0402JR-073K9L - Yageo Phycomp

LDO Linear Regulator ADJ 3.0 A

LT1764AEQ#PBF - Linear Technology

Table 25: Suggested components for VCC voltage supply application circuit using an LDO linear regulator

Figure 43 and the components listed in Table 26 show an example of a low cost power supply circuit, where the

VCC module supply is provided by an LDO linear regulator capable of delivering the specified highest peak /

pulse current, with proper power handling capability. The regulator described in this example supports a limited

input voltage range and it includes internal circuitry for current and thermal 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 as in the circuit described in Figure 43

and Table 26). This reduces the power on the linear regulator and improves the whole thermal design of the

supply circuit.