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PA07A Datasheet(PDF) 4 Page - Cirrus Logic |
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PA07A Datasheet(HTML) 4 Page - Cirrus Logic |
4 / 5 page P r o d u c t I n n o v a t i o n F r o m PA07 • PA07A 4 PA07U GeneraL Please read Application Note 1 "General Operating Con- siderations" which covers stability, supplies, heat sinking, mounting, current limit, SOA interpretation, and specification interpretation. Visit www.Cirrus.com for design tools that help automate tasks such as calculations for stability, internal power dissipation, current limit; heat sink selection; Apex Precision Power’s completeApplication Notes library;Technical Seminar Workbook; and Evaluation Kits. saFeoPeratinGarea(soa) The output stage of most power amplifiers has three distinct limitations: 1. The current handling capability of the wire bonds. 2. The second breakdown effect which occurs whenever the simultaneous collector current and collector-emitter voltage exceed specified limits. 3. The junction temperature of the output transistors. saFeoPeratinGareacurVes The SOA curves combine the effect of these limits. For a given application, the direction and magnitude of the output current should be calculated or measured and checked against the SOA curves. This is simple for resistive loads but more complex for reactive and EMF generating loads. However, the following guidelines may save extensive analytical efforts. 1. For DC outputs, especially those resulting from fault condi- tions, check worst case stress levels against the new SOA graph. For sine wave outputs, use Power Design1 to plot a load line. Make sure the load line does not cross the 0.5ms limit and that excursions beyond any other second breakdown line do not exceed the time label, and have a duty cycle of no more than 10%. For other waveform outputs, manual load line plotting is recommended. Applications Note 22, SOA AND LOAD LINES, will be helpful. A Spice type analysis can be very useful in that a hardware setup often calls for instruments or amplifiers with wide common mode rejection ranges. Tc = 125° C THE RMA L ste ady sta te SE CO ND BR EA KD OW N t = 1m s t = 5m s t = 0.5 ms .2 .3 .4 .6 .8 1.0 1.5 2.0 3.0 4.0 5.0 10 15 20 25 30 35 40 50 60 70 80 100 Tc = 85°C SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE VS – VO (V) 2. The amplifier can handle any reactive or EMF generating load and short circuits to the supply rail or common if the current limits are set as follows at T C = 85°C: SHORT TO ±V S SHORT TO ±V S C, L, OR EMF LOAD COMMON 50V .21A .61A 40V .3A .87A 30V .46A 1.4A 20V .87A 2.5A 15V 1.4A 4.0A These simplified limits may be exceeded with further analysis using the operating conditions for a specific application. 3. The output stage is protected against transient flyback. However, for protection against sustained, high energy flyback, external fast-recovery diodes should be used. tHerMaLsHutdownProtection The thermal protection circuit shuts off the amplifier when the substrate temperature exceeds approximately 150°C.This allows heatsink selection to be based on normal operating conditions while protecting the amplifier against excessive junction temperature during temporary fault conditions. Thermal protection is a fairly slow-acting circuit and therefore does not protect the amplifier against transient SOA violations (areas outside of the T C = 25°C boundary). It is designed to protect against short-term fault conditions that result in high power dissipation within the amplifier. If the conditions that cause thermal shutdown are not removed, the amplifier will oscillate in and out of shutdown. This will result in high peak power stresses, will destroy signal integrity and reduce the reliability of the device. currentLiMit Proper operation requires the use of two current limit resis- tors, connected as shown in the external connections diagram. The minimum value for R CL is .12Ω, however, for optimum reliability it should be set as high as possible. Refer to the “General Operating Considerations” section of the handbook for current limit adjust details. 1 Note 1. Power Design is a self-extracting Excel spreadsheet available free from www.Cirrus.com |
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