u-blox SARA-R4 Series System Integration Manual

Contents

SARA-R4 series - System Integration ManualUBX-16029218 - R06 Design-inPage 48 of 1022.3.2 Module reset (RESET_N)2.3.2.1 Guidelines for RESET_N circuit designSARA-R4 series RESET_N is equipped with an internal pull-up; an external pull-up resistor is not required.If connecting the RESET_N input to a push button, the pin will be externally accessible on the application device.According to EMC/ESD requirements of the application, an additional ESD protection device (e.g. the EPCOSCA05P4S14THSG varistor) should be provided close to accessible point on the line connected to this pin, asdescribed in Figure 19 and Table 16.ESD sensitivity rating of the RESET_N pin is 1 kV (HBM according to JESD22-A114). Higher protectionlevel can be required if the line is externally accessible on the application board, e.g. if an accessible pushbutton is directly connected to the RESET_N pin, and it can be achieved by mounting an ESD protection(e.g. EPCOS CA05P4S14THSG varistor) close to accessible point.An open drain output or open collector output is suitable to drive the RESET_N input from an applicationprocessor, as described in Figure 19.The RESET_N input pin should not be driven high by an external device, as it may cause start up issues.SARA-R4 series18 RESET_NPower-onpush buttonESDOpenDrainOutputApplicationProcessorSARA-R4 series18 RESET_NTP TPFigure 19: RESET_N application circuits using a push button and an open drain output of an application processorReference Description RemarksESD Varistor for ESD protection CT0402S14AHSG - EPCOSTable 16: Example of ESD protection component for the RESET_N application circuitsIf the external reset function is not required by the customer application, the RESET_N input pin can beleft unconnected to external components, but it is recommended providing direct access on theapplication board by means of an accessible test point directly connected to the RESET_N pin.2.3.2.2 Guidelines for RESET_N layout designThe RESET_N circuit require careful layout due to the pin function: ensure that the voltage level is well definedduring operation and no transient noise is coupled on this line, otherwise the module might detect a spuriousreset request. It is recommended to keep the connection line to RESET_N pin as short as possible.