Overview
4
SBOU208 – June 2018
Copyright © 2018, Texas Instruments Incorporated
OPA521EVM User's Guide
1.3
General Information About the OPA521EVM
This EVM configures the OPA521 device in an ac-coupled inverting amplifier allowing users to easily
evaluate the drive capability of the device. The EVM is based on a 5-inch × 3.5-inch (12.7-cm × 8.9-cm)
PC board that accommodates the QFN-20 package with bottom side power pad.
An illuminated red LED (D4) indicates that the OPA521 is operating normally and when turned off it
indicates that the device is in thermal shutdown. When off a red LED (D5) indicates the OPA521 output is
current limited. The output current limits can be selected by positioning the shunt on jumper JMP4 (J12) to
ground for maximum current output or to R10 which can be populated to the appropriate value with the
equations in
1.4
Supply Voltage Considerations for the OPA521EVM
The OPA521 device is able to operate with a single supply, ground, and V+ (7 V -24 V). Although the
supply range of the OPA521 device can operate up to 24-V single supply, the EVM has been designed to
be used up to 17.8-V single supply range due to the TVS diode (D1) attached on the supply to ground
(see
Two PA power-supply pins and two PA ground pins are available to provide a path for the high currents
associated with driving the low impedance of the ac mains. Connecting the three PA supply pins together
is recommended. TI also recommends placing a 47-
μ
F to 100-
μ
F bypass capacitor in parallel with a 100-
nF capacitor as close as possible to the device. Take care when routing the high-current ground lines on
the PCB to avoid creating voltage drops in the PCB ground that may vary with changes in load current.
The OPA521 operational amplifier also requires a digital supply voltage between 2 V and 5.5 V above the
negative supply applied to the amplifier. A fixed output regulator TPS7A1633 was used on the EVM for a
3.3-V supply to fulfill this requirement.
1.5
Input, Output, and Power Supply Protection
Power-line communications are frequently harsh operating environment for electrical components
connected to the ac line. Noise or surges from electrical anomalies such as lightning, capacitor bank
switching, inductive switching, or other grid fault conditions can damage high-performance integrated
circuits if they are not properly protected. The OPA521 can survive even these harsh conditions, but
several simple recommendations must be followed. One recommendation is to clamp as much of the
electrical disturbance before it reaches the OPA521 device with a multi-layer approach using metal-oxide
varistors (MOVs), transient voltage suppression diodes (TVSs), Schottky diodes, and a zener diode.
This EVM has current-steering diodes (B130-13-F), D2 and D3, which were placed at the output of the
OPA521. In the unlikely event a transient surge increases the output pin of the PA beyond its power-
supply rail, low-drop Schottky diodes can steer the current around the OPA521 to ground. Maintaining a
low forward voltage drop on the Schottky diode is recommended for maximum protection. If the Schottky
diode that connects the output of the PA to the power-supply rail turns on and becomes forward-biased, it
is important to steer the current to ground without significantly disturbing the PA power-supply voltage.
Placing a zener or transient voltage suppressor (TVS) diode at the PA power-supply pins to ground
provides a low-impedance path for surges that attempt to raise the power-supply voltage beyond the
absolute maximum rated voltage for the OPA521.
The OPA521EVM has a TVS diode (SMCJ16A-TP) populated in socketD1. When choosing a suitable TVS
or zener-diode, several points must be considered – such as the power supply voltage levels during
normal operation and the expected electrical overstress (EOS). TVS diode was used on D1 and limits the
operating supply to a maximum limit of 15 V. D1 can be replaced with a TVS diode with A procedure how
to select a well-fitting TVS can be found in the following blog: