Introduction: In the portable electronics market, wireless networks allow people to communicate effectively anywhere, anytime, without wires. This is one of the key factors to consider when designing portable electronics. A wireless modem is connected to a wireless network rather than a telephone system. Connect your wireless modem directly to your wireless Internet service provider. Global Mobile (GSM) and General Packet Radio System Service (GPRS) wireless modems, powered by VBUS lines provide an excellent way to implement the portable device environment. However, this modem design causes power management issues, as GSM and gprs transmitters require up to 2A of peak current, which exceeds the maximum current capacity of USB power sources. Now, most USB ports can only supply up to 1A at 5V. For better reliability, designers must consider several design factors; including input overcurrent protection (OCP) sources to avoid overloading the USB power supply, a robust buck converter to fully utilize limited input sources and bulk output capacitors Transmission in GSM and gprs. fpf2195, intellimax 8482 ; combination switch for loads, FAN8060 DC-DC converter provides GSM/GPRS modem designer with input OCP and maximum output current limit to meet the requirements of power pulse loads. The fpf2195 intellimax is a functional load switching limit with adjustable current from 0.15 to 1.5A and low conduction resistance.

The FPF2195 can be mounted on a small PWB (Printed Wiring Board) to maintain healthy thermal performance. The FAN 8060 is a synchronous step-down dc/dc converter at 1.2 MHz frequency, allowing the low profile inductor to safely charge the large output capacitor with 95% efficiency. FAN8060 maximum output current protection prevents shutdown of hub system conditions during output short circuit. GSM/GPRS Power Requirements The system requires up to 2A peak current when transmitting signals through the carrier, GSM and GPRS. This requires a pulsating current power management design for a longer period of time under normal conditions. The GSM transmitter consumes a peak current of 2 A for a single slot cycle for a slot of eight slots for 577 microseconds. A gprs10 class transmitter (two upstream slots) requires the same peak current amplitude, 1.15ms out of 8 for 2 slots. In the other six or seven slots, the current drops to about 100mA, so average. Pulse load current for GSM and 570mA is 340mA for gprs. The figure shows the transmission model of GSM and GPRS used to evaluate the power management circuit described in this paper.

The rectangular current pulses represent the worst-case GSM/GPRS modem loads that guarantee the smooth running of the power supply design. To meet this pulse load condition, designers should consider several aspects of USB-based gsm/gprs wireless modem design input sources. First, the power supply should not overload the limited power specification of a self-powered USB hub. Although the power specification is 5V and 500mA, there seems to be some margin with the current supply capability as most USB hubs on the market can supply up to 1A to cover downstream variable portable applications. Second, the DC/DC buck converter should cover periodic 2A input current limited pulsed load conditions. Also, it should regulate the 3.6V output amplifier required by most power supplies. Finally, an appropriate reservoir output capacitor should be placed in front of the power amplifier to provide pulsed current during transmission. Combination of FPF2195 and FAN8060

The FPF2195 offers three different current limit operations: auto restart, shutdown after blanking, and current source type (see Table 1). The FPF2195 has an adjustable current limit that allows programming the range of desired OCP levels with an external resistor. This will result in ±25% of the current limit accuracy. In the figure, an external resistor of 900 Ω is used (see Equation 1). This prevents overloading the USB input source. Control the main 5V input line to reduce conduction losses, a typical conduction resistance of 44MΩ at 5V is recommended. The 1mm x 1.5mm x 0.65mm WLCSP package allows designers to use the pwb space more efficiently with its 140°C thermal shutdown, 10°C hysteresis protection from the FPF2195 into thermal runaway.

Use a synchronous buck converter with OCP's FPF2195, FAN8060, A 1A to manage 2A pulsed load applications. Its fixed switching frequency of 1.2 MHz allows for low profile inductors, which are ideal for compact power management applications. User-defined external compensation provides more design flexibility to meet the dynamic characteristics that require bulk capacitors under most pulsed load conditions. Using a soft-start pin, the start-up time is adjustable, eliminating the need for large inrush currents to charge the storage capacitor. The diagram shows charging the output capacitor. And your rise time is 23ms, the 82nf capacitor is used to slowly turn on the system. The pins of this synchronizer can be used for two maximum load current limiting functions and improved EMI characteristics. When the sync pin is connected to VIN to ground, the inductor current peak is limited to 0.6a and 1.2a respectively. In addition, when applying a PWM signal from the external sync pin, the internal oscillator is synchronized to improve EMI characteristics. Based on the size and duration of the GSM/GPRS pulse pattern, the output capacitor is selected to meet the input voltage drop of the power amplifier. Ideally, this should be within the recommended minimum input value range. Assuming the input capacitor provides energy to the load in transfer mode, the ESR (equivalent series resistance of the output capacitor) is causing the output voltage to drop. The output voltage drop is defined by the equation: where I pulse and T pulse are pulses and cout is the output capacitance. This represents the worst case ignoring input current provided by the FAN8060 and FPF2195 power supplies. In this design, the two 1500µF TPME158K004R0015 tantalums use capacitors from AVX, each with an ESR of 15MΩ.

The external compensation circuit of the fan8060 is optimized for two 1500µF output capacitors and 2A peak pulse load conditions. Figure shows transient dynamic response using GSM/GPRS Class-10 pulse load verification. In Figure 7, it is assumed that the 2A peak lasts for 1.15 ms, representing the worst case. In GSM mode with a 577µs pulse load, the fan drops 300mV at 8060V and recharges the output capacitor for 1.5ms. In gprs mode, vout is reduced to 3.08v and Vout is charged for 2 ms. Vout drops 300 to 520mv in most power amplifiers. Table 2 shows a performance comparison of 10 types of communication between gsm and gprs.

Protection and Efficiency The fpf2195 and fan8060 offer two key advantages. The FPF2195 provides input OCP to ensure that pulse loads do not accidentally reset the hub side of the USB power management block during GSM/GPRS transfers. The Fan 8060 provides the required 2A peak current and charges the output capacitor. This limits the input current of a 5V USB input source to 600mA . Also, the FAN8060 provides the maximum value. The output current limit protection prevents the constant short state under the output load. As shown in the figure, when the inductor current of the fan 8060 reaches the preset threshold value under short conditions, the internal error amplifier signal is pulled to the ground, and the inductor current drops to zero. Until the inductor current rises to the output ocp threshold, the input current is limited to 600mA by the FPF2195 to ensure that the output short circuit condition does not affect the USB input capacity.

The efficiency of the FPF2195 and FAN8060 power supplies to reach 95% of the average current consumption range shown is shown in the graph. The average load current GSM and GPRS transmissions during 4.62ms are 340mA and 570mA, respectively.