Texas Instruments OPA462EVM Manuale utente

SBOU175–October 2019

OPA462EVM

User's Guide

SBOU175–October 2019

OPA462EVM

This user's guide describes the characteristics, operation, and use of the evaluation module (EVM) for the

OPA462. The EVM is designed to evaluate the performance of the devices in both single and dual-supply

configurations. This document also includes the schematic, printed circuit board (PCB) layout, and a bill of

materials (BOM). Throughout this document the terms evaluation board,evaluation module, and EVM are

synonymous with OPA462EVM.

WARNING

Danger: HIGH VOLTAGE! This evaluation board is intended for

professional use only. It has exposed high voltages. Do not

operate this board without proper high-voltage/high-current safety

practices. Read Section 1.4 before using the EVM.

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Contents

1 Overview ..................................................................................................................... 3

1.1 OPA462.............................................................................................................. 3

1.2 OPA462EVM ........................................................................................................ 3

1.3 Related Documentation............................................................................................ 3

1.4 Evaluation Module Limitations and Cautions.................................................................... 3

2 Getting Started............................................................................................................... 4

2.1 Power Supplies ..................................................................................................... 4

2.2 Jumpers.............................................................................................................. 4

2.3 Inputs................................................................................................................. 4

2.4 Outputs............................................................................................................... 4

2.5 Enable or Disable (E/D)............................................................................................ 4

2.6 Status Flag........................................................................................................... 5

3 Application Circuits .......................................................................................................... 6

3.1 Improved Howland Current Pump................................................................................ 6

4 Schematic, PCB Layout, and Bill of Materials ........................................................................... 9

4.1 EVM Schematic..................................................................................................... 9

4.2 EVM Default Configuration....................................................................................... 10

4.3 PCB Layout ........................................................................................................ 11

4.4 Bill of Materials .................................................................................................... 12

List of Figures

1 Practical, 20-mA, Improved Howland Current-Pump Circuit........................................................... 6

2 Improved Howland Current Pump Output-Voltage Compliance Range .............................................. 7

3 Improved Howland Current Pump Applied as a Peak AC-Current Generator....................................... 8

4 OPA462EVM Schematic.................................................................................................... 9

5 OPA462EVM Default Configuration ..................................................................................... 10

6 OPA462EVM PCB Layout ................................................................................................ 11

List of Tables

1 Related Documentation..................................................................................................... 3

2 Jumper Table................................................................................................................. 4

3 OPA462EVM BOM......................................................................................................... 12

Trademarks

PowerPAD is a trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

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Overview

SBOU175–October 2019

OPA462EVM

1 Overview

1.1 OPA462

The OPA462 is a precision power amplifier capable of operating over a very wide supply range of ±6 V to

±90 V, with an input common-mode range that extends to within a few volts from each rail. This amplifier

is composed of an internal differential input amplifier stage, followed by a voltage amplifier, and finally, a

high-current output stage. This device is designed to avoid phase inversion problems that are typically

found in similar op amps. The OPA462 is unity-gain stable, and comes in an SO PowerPAD™ package.

1.2 OPA462EVM

The OPA462EVM is intended to provide basic functional evaluation of the OPA462. The EVM provides the

following features:

• Easy access to pertinent nodes with test points and terminal blocks

• Convenient input and output filtering

• Access to multiple nodes and footprints for compensation

• Protection against power supply sequencing and inductive load kickback

• Configurable for any common amplifier topology, including the improved Howland current pump

• Footprints for providing a flexible reference voltage

1.3 Related Documentation

The following documents listed in Table 1 provide information about TI's integrated circuits and support

tools for the OPA462EVM.

Table 1. Related Documentation

Document Literature Number

OPA462 Product Data Sheet SBOS803

OPA445 Product Data Sheet SBOS156

1.4 Evaluation Module Limitations and Cautions

As a result of the high common-mode input voltage rating of the OPA462, evaluation of the device often

involves high-voltage operation. As a difference amplifier, it may also be used in current-sensing

applications. In addition to voltage and current limitations, proper electrostatic discharge precautions are

recommended.

1.4.1 High Voltage Warning

The OPA462 is rated for supply voltages up to ±90 V (180 V for single supply), and common-mode input

voltages up to ±85 V. When using the device and EVM under such circumstances, all proper safety

practices must be followed. Do not apply more than rated voltages. See the OPA462 data sheet for

additional information.

1.4.2 Electrostatic Discharge Caution

Many of the components on the OPA462EVM are susceptible to damage by electrostatic discharge (ESD).

Customers are advised to observe proper ESD handling precautions when unpacking and handling the

EVM, including the use of a grounded wrist strap at an approved ESD workstation.

CAUTION

A wrist strap may only be used with circuit voltages less than 100 V. For circuit

voltages equal to or greater than 100 V, use an ionizer.

Getting Started

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OPA462EVM

2 Getting Started

This section explains the connectors and jumpers, and details the basic EVM functionality.

2.1 Power Supplies

The OPA462EVM can be configured from ±6 V to ±90 V for dual supply operation, or from 12 V to 180 V

for single-supply operation. Shorting pins 2 and 3 of J5 sets the EVM to single supply, and shorting pins 1

and 2 of J5 sets up the EVM for dual supplies. The OPA462 is capable of sourcing or sinking up to 30 mA

of current. Power is provided to the EVM through J2 (V+) and J1 (V–). Take care to select supplies

capable of providing the required power for the application. Use a supply capable of supplying at least

twice the anticipated current at the intended operating voltage.

2.2 Jumpers

There are six jumpers located on the OPA462EVM. The jumper functions are summarized in Table 2.

Table 2. Jumper Table

Jumper Function

J3 Enable or disable (E/D) common configuration

J4 Enable or disable (internal or external)

J5 Sets the negative supply to GND for single-supply operation.

J7 Selects inverting input (external or GND)

J10 Selects noninverting input (external or GND)

J12 Sets the reference voltage at the noninverting pin

2.3 Inputs

The inputs to the EVM can be any signal within the common-mode voltage range. BNC connectors are

available at both inputs to allow for easy interfacing with signal generators or other equipment.

Additionally, signals can be input using test points TP12 (IN–) and TP14 (IN+).

Jumpers J7 and J10 set the voltages seen at IN– and IN+, respectively. Short pins 2 and 3 of these

jumpers to set the inputs to GND. Short pins 1 and 2 to allow whatever voltages present at the input BNCs

to be passed to the op amp.

2.4 Outputs

The output of the EVM can be monitored from TP13. A BNC connector, J8, and terminal block, J11, are

also provided to interface with other equipment or circuits. The EVM includes footprints for a load resistor,

load capacitor, and an RC snubber network. If significant power is going to be driven into the load, use

external loads.

2.5 Enable or Disable (E/D)

The OPA462 incorporates a disable feature that can be set using jumpers J3 and J4 on the EVM. The

disable is accomplished without disturbing the input signal path, which helps save power in addition to

protecting the load. Jumper J3 sets the voltage of the E/D Com pin, which can be set to either the

negative rail or GND. The voltage at the E/D Com pin serves as the reference voltage for the E/D pin. J4

sets the voltage at the E/D pin. The device is enabled by floating the E/D pin, or by forcing the E/D pin

high using an external voltage. If forcing the E/D pin high, the pin must be pulled at least 2.5 V greater

than the E/D Com pin, but should not be pulled any more than 5 V greater than the E/D Com pin. Shorting

the E/D pin to the E/D Com pin disables the device.

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Getting Started

SBOU175–October 2019

OPA462EVM

2.6 Status Flag

The OPA462 incorporates a status flag pin to indicate overcurrent or overtemperature conditions. This pin

is an open-drain, active-low output that allows the pin to be easily interfaced with standard low-voltage

logic. The pin goes active if the junction temperature of the device rises to greater than 150°C, and resets

after the device cools to 130°C. Additionally, the pin goes active if the device attempts to source more

than the maximum continuous current of 30 mA. The status flag can be monitored from TP2, and an

external pullup voltage can be input on TP11.

2.6.1 Circuit Protection

The OPA462EVM is protected from inductive surges and power supply transients with the use of

Schottkey diodes on the amplifier output and transient voltage suppressors on the power supply inputs.

See D1, D2, D3 and D4 on the schematic shown in Figure 4, and in the BOM shown in Table 3 at the end

of this document.

In addition, footprints have been provided for optional components Q1 and Q2. These may be used to

protect the amplifier inputs from voltage transients that briefly exceed the maximum input voltage. See the

BOM at the end of this document for the recommended part number.

Application Circuits

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OPA462EVM

3 Application Circuits

The OPA462EVM may be configured in most standard op amp circuits. See the OPA462 data sheet for

typical applications.

3.1 Improved Howland Current Pump

The OPA462EVM can be configured as an improved Howland current pump that provides an output

current proportional to a single- or differential-input voltage. The improved Howland current pump is

described and analyzed in section 3 of the A Comprehensive Study of the Howland Current Pump

application report. Information about how the current-pump resistor values are determined for a particular

input voltage and a corresponding output current is provided in the application report. The report

information is applied here in this section as a practical use for the OPA462EVM.

The OPA462EVM, as configured in Figure 1, sources on an output current of –20 mA when a single-

ended input voltage of 2.5 V is applied to the VP input. If the input voltage sign is reversed, the output

reverses direction and sinks 20 mA. The circuit in Figure 1 provides the resistance values required to

obtain the correct 20-mA output current. The resistor and capacitor labels correspond to those screened

on the OPA462EVM printed circuit board. As shown in Figure 1, when RL is equal to 500 Ω, the sourced

output current level is –20 mA, and Vout is 10 V, as Ohm’s law dictates.

Figure 1. Practical, 20-mA, Improved Howland Current-Pump Circuit

Practical current sources have a limited output voltage range that can be covered. The OPA462 op amp

has a wide output voltage range because of the high-voltage supplies used. The OPA462 data sheet

provides information about the linear output voltage range that should always be observed.

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Application Circuits

SBOU175–October 2019

OPA462EVM

For the improved Howland current pump application, the output voltage (Vout) that is attainable at the load

is further constrained by the voltage drop developed across Rhcp. The 20-mA load current flows through

the resistor, and causes a voltage drop. Therefore, with a fixed 20-mA output current flowing through RL,

there is a limit as to how far Vout can swing. For this example, the limit occurs when Vout reaches

approximately 57.4 V, and RL is 2.87 kΩ. This limit can be seen in Figure 2. Resistor RL can be any value

from 0 Ωto 2.87 kΩ, and the output will remain within the circuit linear compliance range. However, if the

value of RL is increased further, the current pump operation is forced outside the compliance range, and

the output current will no longer remain constant. Thus, increasing the value of RL to greater than 2.87 kΩ

defeats the goal of providing a constant current.

Figure 2. Improved Howland Current Pump Output-Voltage Compliance Range

The improved Howland current pump can be used to generate an ac waveform with a peak current that

corresponds to a maximum specified dc value. A 20-mA dc current source using the OPA462 has been

demonstrated, and will now be used to show how a 20-mA peak ac-current waveform can be realized.

Application Circuits

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OPA462EVM

The same circuit shown in Figure 1 is applied, except the 2.5-VDC VP voltage source in Figure 1 is

replaced by an 100-Hz ac source having a peak voltage of 2.5 V. The peak output current depends on the

peak voltage level applied at the VP input. A triangle wave is used in the example; however, a sine wave,

square wave, or other waveform could be applied instead. Figure 3 shows that a 2.5-V peak input triangle

wave applied to the current pump input, VP, results in a 20-mA peak triangle wave at the output, Vout.

Figure 3. Improved Howland Current Pump Applied as a Peak AC-Current Generator

The improved Howland current pump op amp circuit relies on both negative and positive feedback for

operation; more negative feedback than positive feedback, but that feedback does not always provide

stability. When unity-gain-stable op amps, such as the OPA462, are employed and they drive a resistive

load, the op amp phase margin should be sufficient such that the circuit is stable. However, if the output

load is complex, containing both resistive and reactive components (R±jX), there can be combinations that

degrade the phase margin, and instability results. Degradation of the phase margin often occurs when the

current pump is used to drive loads that are predominantly inductive.

The OPA462EVM has a number of positions where component may be added to stabilize the various

OPA462 amplifier and improved Howland current pump configurations that are supported by the EVM.

Some of the component locations that are used for this purpose are R6 (ISO), R5 (Rng), C12 (Cng, noise

gain), R10 (Rsn), C16 (Csn, snubber), and C9 and C10 in the feedback loop. Compensation, when

required, is determined based on the particular circuit to which the OPA462 is being applied. Op amp

stability and compensation is a vast subject covered in numerous TI documents, and TI training programs

such as TI Precision Labs – Op Amps.

GND

TP1

V+

TP9

0.1uF

TP3 TP4

V+

GND

R9RL

TP13

V+

E/D

E/D Com

GND

E/D

Op Amp Supplies and Bulk Decoupling

TP10

E/D EXT

GND

0.1uF

Enable/Disable Configuration

R12 Rref

TP15

VREF Ext

10k

GND

J12

VREF Select

GND

V-

SF Pull-Up

GND

R11

Rf+

-In Select

TP12

TP14

J10

+In Select

GND

R10

Rsn

GND

0.1uF

C15

GND

0.1uF

C11

GND

J11

Vout

GND

R5 Rng

GND

R6 Riso

R7 Rhcp

TP5 TP6

V-

TP2

C13

C16

Csn

Power Supply

Minimum: 12V (+/-6V)

Maximum: 180V (+/-90V)

TP11

SF EXT

GND

0.1uF

TP16

GND

TPTT 1

V+

TPTT 9

0.1uF

TPTT 3 TPTT 4

V+

GND

TPTT 5 TPTT 6

V-

Poweww r Supply

Minimum: 12V (+/-6V)

Maxixx mum: 180V (+/-90V)

TPTT 16

E/D Com

GND

E/D

TPTT 10

E/D EXT

GND

0.1uF

V-

TPTT 2

SF TTPTT 11

SF EXT

GND

0.1uF

V+

V-

1,8

Q1A

6 7

4,5

Q2B

2 3

1,8

Q2A

4,5

Q1B

Input Protection

1,8

Q1A

6 7

4,5

Q2QQ B

2 3

1,8

Q2QQ A

4,5

Q1B

Input Protection

R13

100k

E/D Com

10uF

V+

V-

OPA462IDDAR

100k

Ext

GND

Ext

Int Ext

90V

C10

C12 Cng

C14

C17

C18

-In

+In

Vout

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Schematic, PCB Layout, and Bill of Materials

SBOU175–October 2019

OPA462EVM

4 Schematic, PCB Layout, and Bill of Materials

This section discusses the OPA462EVM hardware schematics, PCB layout and jumper configurations.

4.1 EVM Schematic

Figure 4 depicts the complete OPA46xEVM schematic.

Figure 4. OPA462EVM Schematic

GND

TP1

V+

TP9

0.1uF

TP3 TP4

V+

TP13

V+

E/D

E/D Com

GND

E/D

Op Amp Supplies and Bulk Decoupling

TP10

E/D EXT

Enable/Disable Configuration

10k

GND

V-

SF Pull-Up

-In Select

TP12

TP14

J10

+In Select

GND

0.1uF

C15

GND

0.1uF

C11

GND

J11

Vout

GND

Riso

Rhcp

TP5 TP6

V-

TP2

Power Supply

Minimum: 12V (+/-6V)

Maximum: 180V (+/-90V)

TP11

SF EXT

GND

0.1uF

TP16

V+

V-

100k

E/D Com

Vout

-In

+In

10uF

V+

V-

OPA462IDDAR

100k

Ext

GND

Ext

90V

Schematic, PCB Layout, and Bill of Materials

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4.2 EVM Default Configuration

The OPA462EVM ships in a standard amplifier configuration with a noninverting gain of 11. Figure 5 shows the schematic for the default

configuration. Any components shown on the complete schematic but not on this schematic are optional and not installed.

Figure 5. OPA462EVM Default Configuration

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