Power Supply Pin; Design Guide - SimCom SIM5215 Hardware Design

Figure 8: VBAT voltage drop during burst emission (GSM/GPRS)
3.1.1

Power Supply Pin

Six VBAT pins are dedicated to connect the supply voltage.
Table 5: Pin description
Pin type Pin name
POWER VBAT
Note: 1. When the module is power off, users must pay attention to the issue about current leakage. Refer to Chapter
3.10.2 Note2.
3.1.2

Design Guide

Make sure that the input voltage at the VBAT pin will never drop below 3.3V even during a transmit burst
when the current consumption rises up to more than 2A. If the power voltage drops below 3.3V, the
module may be shut down automatically. Using large tantalum capacitors (above 100uF) will be the best
way to reduce the voltage drops. If the power current cannot support up to 2A, users must introduce larger
capacitor (typical 1000uF) to storage electric power, especially GPRS multiple time slots emission.
For the consideration of RF performance and system stability, some multi-layer ceramic chip (MLCC)
capacitors (0.1/1uF) need to be used for EMC because of their low ESR in high frequencies. Note that
capacitors should be put beside VBAT pins as close as possible. Also User should minimize the PCB trace
impedance from the power supply to the VBAT pins through widening the trace to 80 mil or more on the
board. The following figure is the recommended circuit.
SIM5215&SIM5216_Hardware Design_V2.02
Min Typ
3.3 3.8
21
Smart Machine Smart Decision
Max Unit
4.2 V
2012-08-31