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LTE-A Module Series
EM121R-GL Hardware Design
EM121R-GL Hardware Design 29 / 80
3.3.2. Reference Design for Power Supply
Power design is important for the module, as the performance of the module largely depends on the
power source. If the voltage difference between the input and output is not too high, it is suggested that an
LDO is used when supplying power for the module. If there is a big voltage difference between the input
source and the desired output (VCC = 3.7 V Typ.), a buck DC-DC converter is preferred.
The following figure shows a reference design for +5 V input power source based on the DC-DC
TPS54319. The typical output of the power supply is about 3.7 V and the maximum load current is 3.0 A.
D1
TVS
PWR_IN
C8
220
μ
F
C11
10 pF
C10
33 pF
C9
100 nF
+
R1
205k
U1
Q1
NPN
R8
47k
R7
4.7k
PWR_EN
R4
182k
PWR_OUT
L1
1.5
μ
H
VIN
VIN
VIN
EN
VSNS
COMP
RT/CLK
SS
PH
PH
PH
BOOT
PWRGD
GND
GND
AGND
VFB
R5
383k 1%
R6
100k 1%
C6
100 nF
PWRGD
EP
R2
80.6k
C7
10 nF
R3
10k
C4
10 nF
C5
NM
VFB
C2
100 nF
C3
33 pF
C1
470
μ
F
+
Figure 7: Reference Circuit for the Power Supply
To avoid damaging the internal flash, do not switch off the power supply directly when the module is
working.
3.4. Turn on
FULL_CARD_POWER_OFF#
is used to turn on/off the module. When the input signal is asserted high (≥
1.19 V), the module will be turned on. When the inpu
t signal is driven low (≤ 0.2 V) or Tri-stated, the
module will be turned off.
This input signal is 3.3 V tolerant and can be driven by either 1.8 V or 3.3 V GPIO. Also, it has internally
pulled down with a 100 kΩ resistor.
The following table shows the definition of FULL_CARD_POWER_OFF#.
NOTE