Datasheet

Microphone Input
3-3
Setup Guide
3.2 Microphone Input
Dynamic and condenser microphones or audio test equipment are connected
to the PGA2500EVM input through combo connector J1. The combo connec-
tor combines both a 3-pin female XLR and a 1/4-inch TRS jack for connecting
to microphones and test signal sources. Both the XLR and TRS jacks are wired
for a balanced input. Figure 3−2 illustrates the combo connector pin configura-
tion for the PGA2500EVM.
Figure 3−2. Microphone Input Connector Configuration
1
2
3
Hot(+),toV
IN
+
Cold (
−
), to V
IN
−
Shield, to EGND
Hot (+), to V
IN
+
Cold (
−
), to V
IN
−
Shield, to EGND
R
T
S
The microphone input includes 1000pF capacitors configured as an EMI filter
to help suppress electromagnetic interference present at the preamplifier in-
put. Additional filtering may be required in the customer’s end application cir-
cuit, depending on the operating environment.
3.3 Phantom Power Connections
The PGA2500EVM supports connection of a phantom power source across
the inputs of the preamplifier using terminal block J2. The voltage source is
connected to the hot (+) and cold (−) sides of the preamplifier input through
6.81kΩ resistors. Phantom power may be operated at voltages up to +50V DC.
Phantom power is required for condenser microphones, but should not be ap-
plied when using dynamic microphones, as they may be subject to damage if
phantom voltage is applied. When using a dynamic microphone, terminals 3
and 4 of jumper JMP1 should be shorted, while terminals 1 and 2 remain open.
When using a condenser microphone requiring a phantom power source, ter-
minals 1 and 2 of jumper JMP1 should be shorted, while terminals 3 and 4 re-
main open.
3.4 DC Blocking Capacitors
Capacitors C
19
and C
20
are utilized as DC blocking capacitors. They provide
AC-coupling to the microphone input, as well as blocking the phantom voltage
from reaching the PGA2500 input terminals when using a condenser micro-
phone. The blocking capacitors are selected in order to not degrade the dy-
namic performance of the PGA2500. The surface-mount aluminum electrolyt-
ic capacitors shown in the Bill of Materials (see Table 4−1) are installed by de-
fault at the factory. The PGA2500EVM also supports the use of through-hole
capacitors for C
19
and C
20
. If using an alternative capacitor, use components
rated for 50WV minimum, with 63WV or higher recommended for long-term
reliability.