Sony Ericsson GS64 - Manual (Page 35)

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The wireless modem has insufficient internal capacitance to supply the
large current peaks during GSM burst transmission - use the following
general guidelines in designing the application power supply.
• Fit a low ESR electrolytic capacitor close to the wireless modem
(>1,000 µF, with an ESR < 100 mΩ)
•
Ensure power supply to wireless modem line resistance is < 200 mΩ
The module has approximately 40µF of internal capacitance across the
VCC pins. During initial power-up the host power supply will have to
charge this capacitance to the operating voltage. This initial in-rush
current may exceed the module’s normal peak current, sometimes
greater than an order of magnitude higher (depending upon the power
supply design) for a short duration (generally a few microseconds).
TIP
CAUTION