Ublox SARA-R4 Series, System Integration Manual

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SARA-R4 series - System integration manual
UBX-16029218 - R20 Design-in Page 55 of 128
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2.2.1.9 Guidelines for removing VCC supply
Removing the VCC power can be useful to minimize the current consumption when the SARA-R4
series modules are switched off or when the modules are in deep sleep Power Saving Mode.
In applications in which the module is paired to a host application processor equipped with a RTC, the
module can execute standard PSM procedures, store NAS protocol context in non-volatile memory,
and rely on the host application processor to run its RTC and to trigger wake-up upon need. The
application processor can disconnect the
VCC supply source from the module and zero out the
module’s PSM current.
The VCC supply source can be removed using an appropriate low-leakage load switch or p-channel
MOSFET controlled by the application processor as shown in Figure 30 , given that the external switch
has provide:
• Ultra low leakage current (for example, less than 1
µ
A), to minimize the current consumption
•
Very low R
DS(ON)
series resistance (for example, less than 50 m

), to minimize voltage drops
• Adequate maximum drain current (see the SARA-R4 series data sheet [1] for module current
consumption figures)
C3
GND
C2 C1 C4
SARA-R4 series
52
VCC
53
VCC
51
VCC
VCC supply source
GND
C5
U1
VOUT VIN
VBIAS
ON
CT
GND
4
V_INT
15
PWR_ON
R1
R2
T1
GPIO
Application
processor
GPIO
GPIO
+
Figure 30: Example of application circuit for VCC supply removal
Reference Description Part Number - Manufacturer
C1 100
µ
F Capacitor Tantalum B_SIZE 20% 6.3V 15m  T520B107M006ATE015 – Kemet
C2 10 nF Capacitor Ceramic X7R 0402 10% 16 V GRM155R71C103KA01 - Murata
C3 100 nF Capacitor Ceramic X7R 0402 10% 16 V GRM155R61A104KA01 - Murata
C4 68 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H680JA01 - Murata
C5 15 pF Capacitor Ceramic C0G 0402 5% 25 V GRM1555C1E150JA01 - Murata
R1, R3 47 k  Resistor 0402 5% 0.1 W RC0402JR-0747KL - Yageo Phycomp
R2 10 k  Resistor 0402 5% 0.1 W RC0402JR-0710KL - Yageo Phycomp
T1 NPN BJT Transistor BC847 - Infineon
U1 Ultra-Low Resistance Load Switch TPS22967 - Texas Instruments
Table 19: Components for VCC supply removal application circuit
☞
It is highly recommended to avoid an abrupt removal of the VCC supply during SARA-R4 series
normal operations: the VCC supply can be removed only after V_INT goes low, indicating that the
module has entered Deep-Sleep Power Saving Mode or Power-Off Mode.
☞
See the section 2.2.1.10 , and in particular Figure 31 / Table 20 , for the parts recommended to be
provided if the application device integrates an internal antenna.