CalAmp LandCell SMC-GPRS Series, Руководство пользователя

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001-0004-829 Rev00
Page 59 of 84
Power Losses and Voltage Drops for GSM/GPRS Cell Module
The cell modules are specified to operate with specific voltage supplies. Voltage supplies may range
from 3.2V to 4.5V as measured on the module’s power connector.
To be on the safe side, it should be assumed that the voltage drop during the TX burst does not
exceed 400mV. This means that if the cell module requires a minimum voltage supply of 3.2V, the
power supply solution should provide at least 3.6V to the cell module.
The SMC-GPRS modem has a built in 3A linear supply which regulates the 5VDC input down to
3.9VDC for the cell module.
SMC-GPRS Power Supply Requirements
The SMC-GPRS modem is designed with a 3A linear supply with two 100uF capacitors on the output.
The 5VDC input voltage level should not dip below 4.6VDC during TX bursts to ensure proper
regulation for the 3.9VDC supplied to the cell module and for the serial port buffer IC (supplied by
the 5VDC input line).
Figure 2 shows an example of a 5VDC source supply dipping to 4.72VDC during these TX burst
cycles. The 3.9VDC regulated line to the cell module stays relatively constant.
Figure 2: Voltage drop during TX bursts
The regulator on the SMC-GPRS modem will provide a post filtering effect, lowering external supply
ripple to the cell module. The current draw on the 5VDC external supply during these TX burst cycles
can be 1.4 Amps.