Smart Machine Smart Decision
9
To increase power efficiency, the switching mode DC-DC converter is preferable, especially when DC input
voltage is quite high. The following figure is the reference design, and it is recommended to reserve a proper
ferrite bead (FB101 in Figure 5) in series for EMI suppression.
Vin
Vout
FB
U101
1
2
3
4
5
LM2596-ADJ
+
100uH
MBR360
L101
C101
+
C102
D102
C103
R102
R101
FB101
330uF
VBAT
2.2K
1K
100uF
1uF
C104
100nF
270R@100MHz
DC INPUT
PWR_CTRL
GND
On/Off
Figure 5: DC-DC power supply reference circuit
For battery-powered application, the 3.7V lithium battery can be connected to SIM8905A VBAT pins directly, but
other types of battery must be used carefully, since their maximum voltage may rise over the absolute maximum
voltage of the module. When battery is used, the total impedance between battery and VBAT pins should be less
than 150
mΩ.
In any case mentioned above, at the VBAT input pins side, please take Figure 6 as a reference:
5.1V
500mW
33pF
VBAT
VBAT_BB
GND
C101
C103
100uF
Module
D101
C105
220uF
VBAT_RF
Figure 6: VBAT input reference circuit
Where C101 is a 100uF tantalum capacitor with low ESR; C105 is a 220uF tantalum capacitor with low ESR;
33pF and 10pF capacitors are used for eliminating the high frequency interference; 5.1V/500mW zener diode can
protect the module against voltage surge.
All of these components should be placed as close to VBAT pins as possible.
Table 1: Recommended zener diode
Vendor
Part number
Power(watts)
Packages
1
On semi
MMSZ5231BT1G
500mW
SOD123
2
Prisemi
PZ3D4V2H
500mW
SOD323
3
Vishay
MMSZ4689-V
500mW
SOD123
