A laser-trimmed monolithic integrated circuit provides excellent low-level signal accuracy and high output voltage and current. The OPA operates from either single or dual supplies for design flexibility. In single supply operation, the input common-mode range extends below ground. The OPA is internally protected against overtemperature conditions and current overloads. In addition, the OPA was designed to provide an accurate, user-selected current limit. This allows the current limit to be adjusted from 0 to mA with a 0 to ?
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A laser-trimmed monolithic integrated circuit provides excellent low-level signal accuracy and high output voltage and current. The OPA operates from either single or dual supplies for design flexibility. In single-supply operation, the input common-mode range extends below ground. The OPA is internally protected against over-temperature conditions and current overloads. In addition, the OPA was designed to provide an accurate, user-selected current limit.
This allows the current limit to be adjusted from 0mA to mA with a 0 to ? A control signal. An input on the pin not only disables the output stage to effectively disconnect the load, but also reduces the quiescent current to conserve power.
The copper tab allows easy mounting to a heat sink or circuit board for excellent thermal performance. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure.
Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
A Sinking 5? V— —VO? The OPA can be used in virtually any op amp configuration. Power-supply terminals should be bypassed with low series impedance capacitors. The technique shown, using a ceramic and tantalum type in parallel, is recommended. Powersupply wiring should have low series impedance. ILIM 1 The low-level control signal 0? A to ?
A also allows the current limit to be digitally controlled with a current-out or voltage-out DAC reference to V— according to the equations given in Figure 3. Figure 3 shows a simplified schematic of the internal circuitry used to set the current limit. The power dissipated by the output transistor is equal to the product of the output current and the voltage across the conducting transistor, VS — VO. F capacitors directly to package power-supply pins.
Basic Circuit Connections. Most behavior remains unchanged throughout the full operating voltage range. Parameters which vary significantly with operating voltage are shown in the typical characteristic curves. Some applications do not require equal positive and negative output voltage swing. Power-supply voltages do not need to be equal. The OPA can operate with as little as 8V between the supplies and with up to 60V between the supplies.
For example, the positive supply could be set to 55V with the negative supply at —5V, or vice-versa. VS — VO? Safe Operating Area. The safe output current decreases as VS — VO increases. Output short-circuits are a very demanding case for SOA.
Increasing the case temperature reduces the safe output current that can be tolerated without activating the thermal shutdown circuit of the OPA Unlike other designs which use a power resistor in series with the output current path, the OPA senses the load indirectly.
This allows the current limit to be set with a 0? In contrast, other designs require a limiting resistor to handle the full output current mA in this case.
For dc signals, power dissipation is equal to the product of output current times the voltage across the con- 8 OPA www. Power dissipation can be minimized by using the lowest possible power-supply voltage necessary to assure the required output voltage swing. For resistive loads, the maximum power dissipation occurs at a dc output voltage of one-half the power-supply voltage.
Dissipation with ac signals is lower. Application Bulletin SBOA explains how to calculate or measure power dissipation with unusual signals and loads. The internal protection circuitry was designed to protect against overload conditions. Continuously running the OPA into thermal shutdown will degrade reliability.
The tab of the DDPAK surface-mount version should be soldered to a circuit board copper area for good heat dissipation. Figure 4 shows typical thermal resistance from junction to ambient as a function of the copper area. A ? Adjustable Current Limit. Activation of the thermal shutdown circuit during normal operation is an indication of excessive power dissipation or an inadequate heat sink. Depending on load and signal conditions, the thermal protection circuit may cycle on and off.
This limits the dissipation of the amplifier but may have an undesirable effect on the load. To estimate the margin of safety in a complete design including heat sink , increase the ambient temperature until the thermal protection is activated. Use worst-case load and signal conditions.
Output Disable with Dual Supplies. One or both of these functions can be utilized on the same device using single or dual supplies. Once shutdown has occurred this voltage drops to approximately mV above the negative rail. Figure 7 gives an example of monitoring shutdown in a single-supply application. Figure 8 provides a circuit for dual supplies. External logic circuitry or an LED could be used to indicate if the output has been thermally shutdown, see Figure Signals that are greater than 10kHz may cause leakage current to increase in devices that are shutdown.
Figure 15 shows the two OPAs in a switched amplifier configuration. Typically the output is shutdown in 1? Figure 5 provides an example of how to implement this function using a single supply. Figure 6 gives a circuit for dualsupply applications. Thermal Shutdown Status with a Single Supply. Output Disable with a Single Supply. Thermal Shutdown Status with Dual Supplies. Figures 9 and 10 provide examples using a single supply and dual supplies, respectively.
This damaging condition can be avoided with clamp diodes from the output terminal to the power supplies, as shown in Figure Schottkey rectifier diodes with a 1A or greater continuous rating are recommended. R2 20k? For normal operation output compensation circuitry is not typically required. F which generally provides excellent stability.
Some variations in circuit values may be required with certain loads. Carbon Motor 0. Motor Drive Circuit. First, the current limit resistor, RCL, is chosen according to the desired output current. The resulting voltage at the ILIM pin is constant and stable over temperature. This voltage, VCL, is connected to the noninverting input of the op amp and used as a voltage reference, thus eliminating the need for an external reference.
The feedback resistors are selected to gain VCL to the desired output voltage level. Both the output voltage and output current are user-controlled. Figure 13 shows a circuit using potentiometers to adjust the output voltage and current while Figure 14 uses DACs. Uses voltage developed at ILIM pin as a moderately accurate reference voltage.
Voltage Source. ILIM V— 4. Resistor-Controlled Programmable Power Supply. Digitally-Controlled Programmable Power Supply. Multiple Current Limit Values. Swap Amplifier. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
Samples may or may not be available. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free RoHS Exempt : This component has a RoHS exemption for either 1 lead-based flip-chip solder bumps used between the die and package, or 2 lead-based die adhesive used between the die and leadframe.