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PA26 Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers |
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5 / 5 page APEX MICROTECHNOLOGY CORPORATION • TELEPHONE (520) 690-8600 • FAX (520) 888-3329 • ORDERS (520) 690-8601 • EMAIL prodlit@apexmicrotech.com ADDITIONAL PA26 PIN FUNCTIONS This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice. PA21/25/26U REV. G FEBRUARY 2000 © 2000 Apex Microtechnology Corp. Figure 3 shows a bootstrap which dynamically couples the output waveform onto the V BOOST pin. This causes VBOOST to swing positive from it's initial value, which is equal to +V S -0.7 V (one diode drop), an amount equal to the output. In other words, if V BOOST was initially 19.3, and the output swings positive 18 Volts, the voltage on the V BOOST pin will swing to 19.3 -0.7 + 18 or 36.6. The capacitor needs to be sized based on a 1K Ω impedance and the lowest frequency required by the circuit. For example, 20Hz will require > 8uF. ISENSE The I SENSE pin is in series with the negative half of the output stage only. Current will flow through this pin only when nega- tive current is being outputted. The current that flows in this pin is the same current that flows in the output (if –1A flows in the output, the I SENSE pin will have 1A of current flow, if +1A flows in the output the I SENSE pin will have 0 current flow). The resistor choice is arbitrary and is selected to provide whatever voltage drop the engineer desires, up to a maximum of 1.0 volt. However, any voltage dropped across the resistor will subract from the swing to rail. For instance, assume a +/– 12 volt power supply and a load that requires +/–1A. With no current sense resistor the output could swing +/–10.2 volts. If a 1 Ω resistor is used for current sense (which will drop 1 Volt at 1 Amp) then the output could swing +10.2, –9.2 Volts. Figure 4 shows the PA26 I SENSE feature being used to obtain a Transconductance function. In this example, amplifier "A" is the master and amplifier "B" is the slave. Feedback from sensing resistors R S is applied to the summing network and scaled to the inverting input of amplifier "A" where it is com- pared to the input voltage. The current sensing feedback imparts a Transconductance feature to the amplifiers transfer function. In other words, the voltage developed across the sensing resistors is directly proportional to the output current. Using this voltage as a feedback source allows expressing the gain of the circuit in amperes vs input voltage. The transfer funcion is approximately: I L= (VIN – VREF) *R IN/ RFB/ Rs In the illustration, resistors R IN, RFB and RS determine gain. VBIAS should be set midway between +Vs and -Vs, Vref is usually ground in dual supply systems or used for level translation in single supply systems. MOUNTING PRECAUTIONS 1. Always use a heat sink. Even unloaded, the PA26 can dissipate up to 3.6 watts. A thermal washer or thermal grease should always be used. 2. Avoid bending the leads. Such action can lead to internal damage. 3. Always fasten the tab to the heat sink before the leads are soldered to fixed terminals. 4. Strain relief must be provided if there is any probability of axial stress to the leads. 10 3 7 5 8 PA26A PA26B +V S ≤ 20V D B1 D B2 C B1 SPEAKER C B2 FIGURE 3. SIMPLE BOOTSTRAPPING IMPROVES POSITIVE OUTPUT SWING. CONNECT PINS 3 AND 10 TO VS IF NOT USED. TYPICAL CURRENTS ARE 12mA EACH. The V BOOST pin is the positive terminal for the load of the second stage of the amplifier. When that terminal is connected to a voltage greater than +V S it will provide more drive to the upper output transistor, which is a darlington connected emit- ter follower. This will better saturate the output transistor. When V BOOST is about 5 Volts greater than +VS the positive output can swing 0.5 Volts closer to the rail. This is as much improvement as is possible. V BOOST pin requires approximately 10–12mA of current. Dynamically it represents 1K Ω impedance. The maximum voltage that can be applied to V BOOST is 40 volts with respect to –V S . There is no limit to the difference between +VS and VBOOST. OPERATING CONSIDERATIONS PA21/25/26 • PA21A/25A VBOOST A B VBIAS +VS VIN VREF –VS OR GND RS RS IL RL RIN RIN R PA26 R RFB RFB FIGURE 4. ISENSE TRANSCONDUCTANCE BRIDGING AMPLIFIER |
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