Wavecom GR64 GSM/GPRS Integrator's Manual page 38

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CAUTION
GR64 Integrators Manual
Page: 38/104
The Wireless CPU 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 CPU (>1,000 µF,
with an ESR < 100 mohm)
Ensure power supply to Wireless CPU line resistance is < 80 mohm
The Wireless CPU 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 Wireless CPU'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).
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