Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 35 of 175
1.5.5 Interface supply (V_INT)
The same voltage domain used internally to supply the digital interfaces is also available on the V_INT pin. The
internal regulator that generates the V_INT supply is a switching step down converter that is directly supplied
from VCC. The voltage regulator output is set to 1.8 V (typical) when the module is switched on and is disabled
when the module is switched off or when the RESET_N pin is forced the low level. The switching regulator
operates in Pulse Width Modulation (PWM) for high output current mode but automatically switches to Pulse
Frequency Modulation (PFM) at low output loads for greater efficiency, e.g. when the module is in idle-mode
between paging periods.
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.
Name
Description
Remarks
V_INT
Digital Interfaces supply output
V_INT = 1.8V (typical) generated by the module when it is
switched-on and the RESET_N (external reset input pin) is
not forced to the low level.
V_INT is the internal supply for digital interfaces.
The user may draw limited current from this supply rail.
Table 15: Interface supply pin
The V_INT pin ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F). 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) on the line connected to this pin, close to accessible point.
Since it supplies internal digital circuits (see Figure 3), V_INT is not suited to directly supply any sensitive analog
circuit: the voltage ripple can range from 15 mVpp during active mode (PWM), to 70 mVpp in idle-mode (PFM).
V_INT can be used to supply external digital circuits operating at the same voltage level as the digital
interface pins, i.e. 1.8 V (typical). It is not recommended to supply analog circuitry without adequate
filtering for digital noise.
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 detailed electrical
characteristics are described in LISA-U2 series Data Sheet [1].
V_INT can only be used as an output; do not connect any external regulator on V_INT. If not used, this
pin should be left unconnected.
The V_INT digital interfaces supply output is mainly used to:
 Pull-up DDC (I
2
C) interface signals (see section 1.10.2 for more details)
 Pull-up SIM detection signal (see section 1.8 for more details)
 Supply voltage translators to connect digital interfaces of the module to a 3.0 V device (see sections 1.9.2.4,
1.9.4.4 for more details)
 Supply a 1.8 V u-blox 6 or subsequent GNSS receiver (see section 1.10.2 for more details)
 Indicate when the module is switched on and the RESET_N external hardware reset input is not forced low
(see sections 1.6.1.5, 1.6.2 and 1.6.3 for more details)