AN-8019
APPLICATION NOTE
Table 2. Transient Performance Data
Parameter
PA Minimum
GSM Mode
3.0V Minimum
2A for 577µs
-300mV
GPRS Class 10
3.0V Minimum
2A for 1.5ms
-520mV
PA Peak Current
VOUT Drop
Input Current Limit by FPF2195
600mA
600mA
Protection and Efficiency
The FPF2195 and FAN8060 offer two key advantages. The
FPF2195 provides input OCP to ensure the pulsed load
during GSM/GPRS transmission does not damage the USB
hub side of the power management block or cause it to be
reset unexpectedly. The FAN8060 supplies the required 2A
peak current and recharges the output capacitance. This
limits the input current from the 5V USB input source to
600mA. In addition, the FAN8060 provides maximum
output current limit protection, which protects against a
dead-short condition at the output load, as shown in Figure
8. As soon as the FAN8060’s inductor current reaches a
preset threshold value at the short condition, the internal
error amplifier signal is pulled to ground and the inductor
current reduces to zero. Until the inductor current rises to
the output OCP threshold, the input current is limited to
600mA by the FPF2195 to ensure the output short condition
does not affect USB input capacity.
100
96
92
88
84
80
76
72
68
64
0
0. 2
0. 4
0. 6
0. 8
1
Load [A]
Figure 9. Efficiency of FPF2195 and FAN8060
at VIN=5V, VOUT=3.6V
Conclusion
The combination of the FPF2195 and FAN8060 offers a
reliable solution for GSM/GPRS modems powered by a
USB source. The input current protection provided by the
FPF2195 prevents the USB input source from overloading
and the maximum output current limit
Load Current [2A/div.]
Input current
Limit by FPF2195
[500mA/div.]
VIN of FPF2195 [2V/div.]
Author
Ilsoo Yang, Technical Product Marketing, and
SungGeun Yoon, Sr. Applications Engineer
VOUT of FAN8060 [1V/div.]
[20ms/div.]
Figure 8. FAN8060 Output OCP at a Given
Pulse Load of 4A to 0.4A
Related Datasheets
The FPF2195 and FAN8060 power supply reaches 95%
efficiency at the average current consumption range shown
in Figure 9. The average load current over a 4.62ms period
of GSM and GPRS transmission is 340mA and 570mA,
respectively.
FPF2193/4/5 — Full Function Load Switch with Adjustable
Current Limit
FAN8060 — 1.2MHz Synchronous Step-Down DC/DC
Regulator
s.
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 5/3/10
www.fairchildsemi.com
4
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
