u-blox SARA-R4 Series System Integration Manual

Contents

SARA-R4 series - System Integration ManualUBX-16029218 - R06 Design-inPage 35 of 1022.2 Supply interfaces2.2.1 Module supply (VCC)2.2.1.1 General guidelines for VCC supply circuit selection and designAll the available VCC pins have to be connected to the external supply minimizing the power loss due to seriesresistance.GND pins are internally connected. Application design shall connect all the available pads to solid ground on theapplication board, since a good (low impedance) connection to external ground can minimize power loss andimprove RF and thermal performance.SARA-R4 series modules must be sourced through the VCC pins with a proper DC power supply that shouldmeet the following prerequisites to comply with the modules’ VCC requirements summarized in Table 6.The proper DC power supply can be selected according to the application requirements (see Figure 10) betweenthe different possible supply sources types, which most common ones are the following: Switching regulator Low Drop-Out (LDO) linear regulator Rechargeable Lithium-ion (Li-Ion) or Lithium-ion polymer (Li-Pol) battery Primary (disposable) batteryMain SupplyAvailable?BatteryLi-Ion 3.7 VLinear LDORegulatorMain SupplyVoltage > 5V?Switching Step-DownRegulatorNo, portable deviceNo, less than 5 VYes, greater than 5 VYes, always availableFigure 10: VCC supply concept selectionThe switching step-down regulator is the typical choice when the available primary supply source has a nominalvoltage much higher (e.g. greater than 5 V) than the operating supply voltage of SARA-R4 series. The use ofswitching step-down provides the best power efficiency for the overall application and minimizes current drawnfrom the main supply source. See section 2.2.1.2 for specific design-in.The use of an LDO linear regulator becomes convenient for a primary supply with a relatively low voltage (e.g.less or equal than 5 V). In this case the typical 90% efficiency of the switching regulator diminishes the benefitof voltage step-down and no true advantage is gained in input current savings. On the opposite side, linearregulators are not recommended for high voltage step-down as they dissipate a considerable amount of energyin thermal power. See section 2.2.1.3 for specific design-in.If SARA-R4 series modules are deployed in a mobile unit where no permanent primary supply source is available,then a battery will be required to provide VCC. A standard 3-cell Li-Ion or Li-Pol battery pack directly connectedto VCC is the usual choice for battery-powered devices. During charging, batteries with Ni-MH chemistrytypically reach a maximum voltage that is above the maximum rating for VCC, and should therefore be avoided.See sections 2.2.1.4, 2.2.1.5, 2.2.1.6 and 2.2.1.7 for specific design-in.Keep in mind that the use of rechargeable batteries requires the implementation of a suitable charger circuitwhich is not included in the modules. The charger circuit has to be designed to prevent over-voltage on VCCpins, and it should be selected according to the application requirements: a DC/DC switching charger is thetypical choice when the charging source has an high nominal voltage (e.g. ~12 V), whereas a linear charger is