Schematic and Layout
7
SBOU208 – June 2018
Copyright © 2018, Texas Instruments Incorporated
OPA521EVM User's Guide
2.2
Input AC-Coupled Capacitor
The input capacitor (CIN) on the OPA521EVM introduces a single-pole, high-pass characteristic to the PA
transfer function. The CIN and PA combination has a band-pass response because of the inherent low-
pass transfer function from the PA. The value of the high-pass cutoff frequency is determined by C
IN
reacting with the input resistance of the PA circuit, and can be determined by Equation 1:
where
•
C
IN
= external input capacitor
•
f
HP
= desired high-pass cutoff frequency
(1)
For example, setting CIN to 3.3 nF results in a high-pass cutoff frequency of 2.9 kHz. Determine the
voltage rating for CIN to withstand operation up to the PA power-supply voltage.
2.3
Current Limit R
SET
Value
The ILIM pin (pin 12) provides a resistor-programmable output current limit for the PA block.
determines the value of the external RSET resistor attached to this pin. where:
where
•
I
LIM
=the value of the desired current limit for the PA
•
R
SET
= the value of the external resistor connected between pin 12 and ground,
(2)
3
Getting Started
This section explains the purpose of the connectors and jumpers, how to configure the EVM and how to
make use of the features provided by the EVM.
3.1
Power Supply
The OPA521EVM is configured only use a single 7-V to 24-V supply, power is provided to the EVM
through 2 banana jacks: AVDD and GND. The power supply must provide the total anticipated current
required in the application. The OPA521 can supply a continuous dc current of 1.9 A, but it is
recommended that the supply should be capable of providing at least 2× the anticipated continuous
current to account for peak current conditions. Make sure any cables used to carry high current are rated
for such service.
Even though the OPA521 operational amplifier is specified for an absolute maximum supply voltage of 26
V, TI recommends that not more than 25 V be applied to the EVM to avoid damage to other parts. For this
reason TVS diode is attached from supply to ground and limits the operating supply to 18V maximum.
3.2
Inputs
The input to the EVM must be an AC signal source such as a signal generator. Note that 50-
Ω
termination
resistors R1 can be utilized on the EVM by placing a short bar on JMP2 (J3). Excessive power dissipation,
under high input voltage conditions, could result in their failure and destruction. The signal presented to
the inverting OPA521 input pin –IN is selected through JMP1 (J5).
3.3
Outputs
Output signals derived from the EVM may be monitored by whatever means required by the user. Often,
an oscilloscope provides a convenient way to observe the output waveform from the OPA521. The output
is brought to a BNC connector (J6) which is intended for the instrument connection and to carry high
output current. The load is intended to be located external to the EVM. The OPA521 can drive a variety of
load types which includes resistors, motors, transducers, etc. some of which may have to dissipate
significant power, or be physically too large to reside on the EVM.