User's Manual

WM620 Hardware User Guide V1.1
All rights reserved by Shenzhen Neoway Technology Co., Ltd. Page 4
Figure 2-1b, Schematic circuit for current test
The current test results related to the ESR of the capacitors and the internal resistance of the power source. A
470uF tantalum electrolytic capacitor or a 1000uF low ESR aluminum electrolytic capacitor is recommended
for C1. Lithium battery is a very low resistance power source. If the VBAT is supplied by a lithium battery,
220uF or 100uF tantalum capacitor can fit the current require for VBAT. These 10uF, 0.1uF, 100pF and 33pF
MLCC capacitors should be placed close to the VBAT pin.
ESD, Lightning Surge or other interferences can rarely cause the WM620 to stop running. Reset the power
supply can recover the module. So the power control is very important in the unattended applications. VCC_EN
in figure 2-2 is the switch to control the power.
The recommended design of power supply is shown in figure 2-2a. In this circuit, with the EN pin of
LDO/DC-DC, power supply can be controlled by the external MCU or other master device. If the LDO or
DC-DC has no EN pin, a low on-resistance P-MOSFET can work as a power switch. The P-MOSFET power
switch shown in Figure 2-2b can replace the function of EN pin.
Figure 2-2a