Pcm Digital Audio - Iridium 9523 Product Developer Manual

Iridium Communications, Inc.
Iridium 9523 Product Developer's Guide
Revision 7.0
It is possible to produce VBOOST in other ways, particularly if the FA has a convenient supply rail that
has high enough voltage and current capacity. Table 8 shows the permissible limits for any VBOOST
supply.
Minimum voltage when capacitors are charged
(limited by minimum input to buck converter to produce PA power rail)
Maximum current into VBOOST pins
(limited by rating of inter-board connector)
Maximum power taken by buck converter
The maximum average power requirement over a 90ms period is 3.1W. The capacitors discharge to
typically 15V during the transmit burst when operating at maximum power. A typical design would have a
power limit of between 5 and 6 Watts (current approximately 0.25 Amp) so that the reservoir capacitors
are replenished in approximately half the allowed time.
If the boost voltage at the start of the transmit burst is below the minimum (27V) then the capacitors may
discharge to below 9.5V, in which case the transmitter power will reduce.
There is a residual VBAT current of about 70mA all the time that the Iridium 9523 is switched on, even
when not in a call. Periodically, the Iridium 9523 will draw about 250mA from the VBAT rail for about
20ms, as it maintains synchronization with the signal from the satellites.
When an Iridium call is in progress, there are two peaks in the current drawn by the VBAT rail in each
90ms frame – one of about 300mA during the transmit time-slot and a slightly smaller one, 250mA, during
the receive time-slot.
At the start of each of period when the receiver or transmitter is active a burst of current will be drawn, as
the radio circuitry switches on. This current is caused by the charging of six 4.7μF capacitors on the
outputs of internal voltage regulators.

3.3 PCM Digital Audio

The Iridium 9523 has two PCM digital audio ports, though only one of these can be in use at any time.
The active port is selected using the AT+CAR command. This setup allows the FA board to provide two
parallel audio paths and switch between them through software instead of hardware. The two ports have
identical signals and timing, as shown in Figure 9. The PCM clock and sync signals are outputs from the
Iridium 9523.
The PCM clock signal has a frequency of 2048 kHz with an accuracy of 1 ppm, but it is derived from an
internal clock source by a fractional divider so each clock high period and low period is either 238.1 ns or
297.6 ns.
The PCM clock, sync and data signal outputs are all timed from the same internal clock and are skewed
by less than 1 ns (at equal load).
Iridium Communications, Inc.
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Table 8: VBOOST Specification
Parameter
Absolute maximum voltage
(limited by capacitor rating)
Maximum recommended voltage
Minimum voltage when enabled
(during transmit time-slot)
Page 21 of 27
Information Contained in this Guide
is Subject to Change Without Notice
Distribution of Guide Restricted
to Product Developers
Value
35V
32V
27V
10.5V
1A
30W