LISA-U series - System Integration Manual
UBX-13001118 - R17
Advance information
System description
Page 38 of 190
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 16: 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 4),
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-U1 series Data Sheet
[1] and
LISA-U2 series Data Sheet
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)