User guide

WA_DEV_FEX20_UGD_002 Rev 004 March 08, 2011 45
Fastrack Xtend User Guide
Interfaces
5.1.2.4.2. Speaker
The speaker outputs are connected in differential mode to reject common mode noise and TDMA
noise.
Speaker outputs are connected to internal push-pull amplifiers and may be loaded down with
components between 32 ~ 150 and up to 1nF. These outputs may be directly connected to a
speaker.
The output power may be adjusted by 2dB steps. The gain of the speaker outputs is internally
adjusted and may be tuned using the AT+VGR command. Furthermore, the digital gain can be
adjusted using AT+WDGR. Refer to document [7] Firmware 7.4a AT Commands Manual (Sierra
Wireless Software Suite 2.31)/Firmware 7.4 AT Commands Manual (Sierra Wireless Software Suite
2.30) for more information about these AT commands.
The following table shows the pin assignments of the speaker outputs.
Table 19. Speaker Outputs Pin Description
(Sub D
15-pin)
Pin #
Signal
I/O
I/O Type
Description
10
CSPK2P
O
Analog
Speaker positive output
15
CSPK2N
O
Analog
Speaker negative output
Figure 20. Equivalent Circuit of CSPK2 Speaker Outputs
Table 20. Electrical Characteristics of CSPK2
Parameters
Min
Typ
Max
Unit
Biasing voltage
CSPK2P and CSPK2N
1.30
V
Output swing
voltage
RL=8: AT+VGR=-1000*; differential
-
-
4
Vpp
RL=32: AT+VGR=-1000*; differential
-
-
5
Vpp
RL
Load resistance
6
8
-

IOUT
Output current; peak value; RL=8
-
-
180
mA
POUT
RL=8; AT+VGR=-1000*;
-
-
250
mW
RPD
Output pull-down resistance at power-down
28
40
52
k
VPD
Output DC voltage at power-down
-
-
100
mV
* The output voltage depends of the output speaker gain set by AT command. Refer to document [7] Firmware
7.4a AT Commands Manual (Sierra Wireless Software Suite 2.31)/Firmware 7.4 AT Commands Manual (Sierra Wireless
Software Suite 2.30). This value is given in dB, but it‟s possible to toggle this to index value.