N723-EA Hardware User Guide
Chapter 5 Application Interfaces
Copyright © Neoway Technology Co., Ltd. All rights reserved.
27
⚫
The maximum input voltage for the module is 4.2 V and the typical value is 3.8 V. For VBAT, the
recommended layout cable width is 2.5 mm or above.
⚫
The TVS diode selected at D1 has a reverse operating voltage (V
RWM
) of 4.5 V, and its peak
power Ppp is 2800 W (tp=8/20 uS). It has the surge protection mechanism. Place the TVS close
to the power input interface to clamp the surge voltage before it enters back-end circuits.
Therefore, the back-end components and the module are protected.
⚫
A large bypass tantalum capacitor (220 μF or 100 μF) or aluminum capacitor (470 μF or 1000
μF) is expected at C1 to reduce voltage drops during bursts. Its maximum safe operating voltage
should be larger than 2 times the voltage across the power supply.
⚫
Place a bypass capacitor (C2, C3, C4, C5) of low-ESR close to the module to filter out high-
frequency jamming from the power supply.
The following circuit design is recommended to control the power supply.
Figure 5-3
Recommended design 2
C1
C2
100k
Ω
R3
C8
C9
10k
Ω
R4
Q2
C
B
E
4.7k
Ω
R1
47k
Ω
R2
0.1
μF
22
μF
C3
C4
C5
C6
C7
100
μF 10μF 0.1μF 100pF 33pF
VIN(3.8V)
PWR_EN
VBAT
1
μF
0.1
μF
S
D
G
Q1
⚫
Select an enhanced p-MOSFET at Q1, of which the safe operating voltage is at least 12 V
(V
dss
=-12 V) and drain current is at least 3.5 A (I
D(MAX)
=-3.5) and Rds is low (Rds
(on)
=108 mΩ).
⚫
Select a common NPN tripolar transistor at Q2. Reserve enough tolerances of R1 and R2 in
design, especially for the situation in which operating voltage of the tripolar transistor might
increase in low temperature; it is recommended that the value of R2 be at least 10 times that of
R1.
⚫
Place C3 close to the module. A large tantalum electrolytic capacitor (220 μF or 100 μF) or
aluminum electrolytic capacitor (470 μF or 1000 μF) can be selected at C3 to improve the
instantaneous large current freewheeling ability of the power supply. Its withstand voltage should
be larger than 2 times the voltage of the power supply.