Figure 4-1 USB port reference circuit diagram
The serial impedance of the USB differential data cables depends on the actual situation. Th e USB
cable routing design must strictly follow the USB2.0 protocol requirements. Cable routing must be
differentiated mode. The control impedance must be 90 Ω.
Electro-static discharge (ESD) components must be as close to the USB port as possible. It is
recommended that you use components with a rated reverse working voltage of 5 V and a junction
capacitance less than 10 pF.
4.2.2 Power Port Introduction
Table 4-2 Power pins
Signal
Name
I/O Description Direct Current Features (V)
Minimum
Value
Typical
Value
Maximum
Value
GND P Power ground
VBUS P USB power supply 4.75 5 5.25
The working power of the MS2131 is provided through the USB port with an input voltage
range from 4.75 V to 5.25 V (typical value: 5 V). Ensure that the power pins are properly
connected during the use of the MS2131 as to maintain its normal performance.
When the MS2131 is dedicated for different applications, attach importance to the power
supply design. In some network environments, when the MS2131works at its largest power
capacity (for example, when it works in GSM mode, a USB voltage dip may occur. Therefore,
make sure the power supply voltage for the host is 3.5 V at the minimum. Otherwise, the
MS2131 may restart.
External power supplies with the current output capacity larger than 2 A are recommended
and that a capacitor of larger than 300 μF and a decoupling capacitor of 0.1 μF must be
paralleled at the power port of the host. When the MS2131 works in GSM mode, its peak
current can reach 2 A. To prevent the MS2131's voltage from dropping to lower than 3.5 V
and help ensure the MS2131 function properly, place a large-capacity capacitor (at least 300
μF) near the USB port.
If the host is powered by batteries, configure a control switching diode or current limiting
chip between the battery power and the MS2131 power port. If a DC/DC converter or
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