User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08 Objective Specification Design-in
Page 95 of 188
2.2.3 Interface supply (V_INT)
2.2.3.1 Guidelines for V_INT circuit design
The V_INT digital interfaces 1.8 V supply output can be mainly used to:
 Pull-up DDC (I
2
C) interface signals (see section 2.6.4 for more details)
 Pull-up SIM detection signal (see section 2.5 for more details)
 Supply voltage translators to connect digital interfaces of the module to a 3.0 V device (see section 2.6.1)
 Supply a 1.8 V u-blox 6 or subsequent GNSS receiver (see section 2.6.4 for more details)
 Indicate when the module is switched on (see sections 1.6.1, 1.6.2 for more details)
Do not apply loads which might exceed the limit for maximum available current from V_INT supply, as
this can cause malfunctions in internal circuitry supplies to the same domain. The SARA-G3 series Data
Sheet [1] and the SARA-U2 series Data Sheet [2] describe the detailed electrical characteristics.
V_INT can only be used as an output; do not connect any external regulator on V_INT.
Since the V_INT supply is generated by an internal switching step-down regulator, the V_INT voltage ripple can
range from 15 mVpp during active-mode or connected-mode (when the switching regulator operates in PWM
mode), to 90 mVpp (SARA-G3 series) or 70 mVpp (SARA-U2 series) in low power idle-mode (when the switching
regulator operates in PFM mode).
It is not recommended to supply sensitive analog circuitry without adequate filtering for digital noise.
V_INT supply output pin provides internal short circuit protection to limit start-up current and protect the device
in short circuit situations. No additional external short circuit protection is required.
ESD sensitivity rating of the V_INT supply pin is 1 kV (Human Body Model according to JESD22-A114).
Higher protection level could be required if the line is externally accessible on the application board.
Higher protection level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG
varistor array) close to accessible point.
If the V_INT supply output is not required by the customer application, since DDC (I
2
C) interface and SIM
detection functions are not used, voltage translations of digital interfaces are not needed and sensing
when the module is switched on is not needed, the V_INT pin can be left unconnected to external
components, but it is recommended providing direct access on the application board by means of
accessible testpoint directly connected to the V_INT pin.
2.2.3.2 Guidelines for V_INT layout design
V_INT digital interfaces supply output is generated by an integrated switching step-down converter, used
internally to supply the digital interfaces. Because of this, it can be a source of noise: avoid coupling with
sensitive signals.