1 Overview

Pa34 is a 7-pin to220 encapsulated high-power operational amplifier launched by apex company. It has a wide input common mode range, includes output current limiting protection function, and has a wide power supply voltage range. In case of single power supply, the power supply voltage range is 5V ~ 40V; In case of dual power supply, the power supply voltage range is ± 2.5V ~ ± 20V. Pa34 has high efficiency, its minimum output current is 2.5A, and the distortion is very small.

Application and installation precautions of pa34 high power operational amplifier

Pa34 power amplifier can be widely used in half bridge or full bridge motor drive, audio power amplifier and many single power supply systems, such as 5V external circuit system, 12V automation system and 28V aerospace system.

2 pin arrangement and main parameters

Figure 1 shows the outline package and pin arrangement of pa34. The main parameters are as follows:

● power supply voltage: 5V ~ 40V;

● output current: the output current of pa34 is related to the voltage value from the power supply to the output. See the SOA curve in Figure 2 for specific parameters;

● internal power consumption: 18.5w;

● differential mode input voltage: ± vs;

● common mode input voltage: + vs ~ – vs-0.5v;

● maximum junction temperature: 150 ℃;

● welding temperature (10s): 300 ℃;

● storage temperature range: – 65 ~ 150 ℃;

● operating temperature range: – 55 ~ 125 ℃.

3 main pin functions

In addition to input, output and power input pins, pa34 also has two special pins vboost and iSense.

3.1 vboost pin

Vboost pin is the positive end of the second stage load of pa34 operational amplifier. When this pin is connected to the 5V power supply higher than + vs, it will provide greater drive to the above transistor (Darlington tube connected to the emitter follower), so it can better saturate the output transistor.

Vboost pin needs about 10 ~ 12mA current and has 1K Ω impedance in dynamic state. The maximum voltage applied to vboost is 40V (relative to – vs)+ The voltage difference between vs and vboost is unlimited.

Figure 3 shows a bootstrap circuit whose coupled output waveform will be output at the vboost pin. This will cause the vboost voltage to swing from its initial value to positive voltage. The swing value is + vs-0.7v (diode voltage drop). The bus between the initial value and the swing is the output of vboost. In other words, if the initial value of vboost is 19.3v and the output swing forward voltage is 18V, the voltage on vboost should be 19.3-0.7 + 18, equal to 36.6v.

3.2 iSense pin

ISense pin can be connected in series with the negative half of the output stage. Only when the negative current is output, the current flows through this pin. At this time, the current flowing through this pin is the same as the current flowing through the output terminal. That is, if – 1A current flows through the output, the iSense pin will have 1A current, while if + 1A flows through the output, the iSense pin current should be zero.

4 Application Description

4.1 secure work area (SOA)

The SOA curve of pa34 can be seen in Figure 2. The safe working curve considers the influence of all restrictions. When there is sufficient output current in the circuit, this situation is relatively simple for resistive loads, but this problem becomes relatively complex for inductive loads and loads with reverse electromotive force (EMF).

Under transient conditions, capacitive and inductive loads are safe only when they meet the condition values given in Table 1. However, for continuous and high-energy feedback, an external fast recovery diode must be connected.

4.2 stability

In order to ensure the stability of the circuit, almost all non complementary output operational amplifiers adopt output stage complementary circuits. For different output current polarities, because their responses in gain and phase do not match, it is very difficult for manufacturers to consider the optimal compensation under the working conditions.

When in use, a 1 Ω resistor can be connected between the output end of pa34 and the ground, and a 0.1 Ω resistor can be connected in parallel μ F capacitance (the power supply and ground must have appropriate bypass capacitance), which can avoid local output oscillation of pa34 in the application circuit.

5 application circuit

Fig. 4 is a bidirectional motor drive circuit designed using two pa34. In the figure, R1 and R2 set the in-phase gain of op amp A to 2.8, and op amp B is a unit gain inverter driven by the output of op amp a. It should be noted that the reference node voltage at the inverting end of operational amplifier B should be set to the midpoint voltage (14V) of the power supply through resistors R5 and R6. When the input is 5V, the output of a is 14V, which is equal to the reference node voltage. Since the output of op amp B is also 14V, the voltage passing through the motor is 0V. When the input voltage is higher than 5V, the current flowing through the motor is from left to right. When the input voltage is lower than 5V, the current flowing through the motor is in the opposite direction, so that the motor rotates in the opposite direction.

6 installation precautions

When installing pa34, pay attention to the following points:

(1) The radiator must be used, because even under no-load condition, the internal power consumption of pa34 is about 3.6W, so the heat dissipation gasket must be used as thermal conductive adhesive.

(2) Try to avoid bending the pins, otherwise the internal circuit structure of the operational amplifier will be damaged.

(3) Before the pin is welded to the fixed end, the backing must be as close to the radiator as possible.

(4) The necessary stress relief must be provided regardless of the extrusion direction of the pin.

Responsible editor: GT

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