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Setup Guide
4.2 Microphone Input
Dynamic and condenser microphones or audio test equipment are connected to the PGA2505EVMV2 input
through combo connector J3. The combo connector 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 4-2
illustrates the combo connector pin configuration for the PGA2505EVMV2.
4.3 Phantom Power Connections
The PGA2505EVMV2 supports connection of a phantom power source across the inputs of the preamplifier
using terminal block J1. The voltage source is connected to the hot (+) and cold (−) sides of the preamplifier
input through 6.81-kΩ resistors. Phantom power may be operated at voltages up to 50 VDC.
Phantom power is required for condenser microphones. When using a condenser microphone requiring a
phantom power source, short pins 1 and 2 of jumper JMP1, and leave pins 3 and 4 open.
Be aware that when using a phantom power source, connect the microphone and cable before
turning on phantom power. Make sure to turn off phantom power before disconnecting the
microphone or cable. Making or breaking the input connection with 48 V may cause large transient
spikes that could damage the PGA2505 or anything connected to the output.
In addition, When using a dynamic microphone, short pins 3 and 4 of jumper J3, and leave pins 1 and 2 open.
4.4 DC Blocking Capacitors
Capacitors C4 and C9 are used as dc blocking capacitors. They provide ac coupling to the microphone input,
as well as block the phantom voltage from reaching the PGA2505 input terminals when using a condenser
microphone. The blocking capacitors are selected to not degrade the dynamic performance of the PGA2505.
The capacitors shown in the bill of materials (see
alternative capacitor, use components rated for 50 V minimum, with 63 V or greater recommended for long-term
reliability.
4.5 Protection Network
Resistors R4 and R14, along with Schottky diodes D5, D6, D7 and D9, provide input protection for the PGA2505
preamplifier when using phantom power, or when the input voltage exceeds the VA+ or VA− power supplies by
more than 350 mV (the approximate turn-on voltage of the Schottky diodes).
A common fault condition is for either the hot (+) or cold (−) input of the preamplifier to be shorted to ground.
With phantom voltage applied, this causes the blocking capacitors to discharge, with a large surge current
presented at the PGA2505 input pins. Without the protection network, the PGA2505 can be permanently
damaged by the surge current, which can reach several amperes in peak magnitude.
The Schottky diodes are forced into conduction during this fault condition, steering most of the charge away from
the PGA2505 device and towards the power supplies. The series resistors can be set to a value that helps limit
the input current; however, take care to avoid adding too much resistance because the added noise can degrade
the overall performance of the preamplifier. The Schottky diodes add a nonlinear capacitance to the input circuit,
10
PGA2505EVMV2 Evaluation Module
Hot (+), to VIN+
Cold (–), to VIN–
Shield, to EGND
Figure 4-2. Microphone Input Connector Configuration
CAUTION
Table
Copyright © 2021 Texas Instruments Incorporated
6-1) are installed by default at the factory. If using an
www.ti.com
R
Hot (+), to VIN+
T
Cold (–), to VIN–
S
Shield, to EGND
SBOU259 – OCTOBER 2021
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