PA94 데이터 시트보기 (PDF) - Cirrus Logic
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PA94 Datasheet PDF : 7 Pages
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PA94
INTERNAL POWER DISSIPATION AND HEATSINK SELECTION
With the unique combination of high voltage and speed of the PA94, traditional formulas for heatsink selection will
falsely lower the apparent power handling capability of this amplifier. To more accurately predict operating tempera-
tures use Power Design1 revision 10 or higher, or use the following procedure:
Find internal dissipation (PD) resulting from driving the load. Use Power Design or refer to Apex Applications Note
1, General Operating Considertaions, paragraph 7. Find total quiescent power (PDQ) by multiplying 0.024A by VSS
(total supply voltage). Find output stage quiescent power (PDQOUT) by multiplying 0.00012 by VSS.
Calculate a heatsink rating which will maintain the case at 85°C or lower.
34" 1%5$ 15%"2$8
Where: TC = maximum case temperature allowed
TA = maximum ambient temperature encountered
Calculate a heatsink rating which will maintain output transistor junctions at 150°C or lower.
34" 5+5"11%% 11%%22065 3+$$8
Where: TJ = maximum junction temperature allowed.
RØJC = AC or DC thermal resistance from the specification table.
Use the larger heatsink of these two calculations.
Power Design is an Excel spreadsheet available free from www.cirrus.com
GENERAL
Please read Application Note 1 "General Operating Considerations" 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 selec-
tion; Apex’s complete Application Notes library; Technical Seminar Workbook; and Evaluation Kits.
CURRENT LIMIT
For proper operation, the current limit resistor (RLIM) must be connected as shown in the external con-
nection diagram. The minimum value is 3.5 ohm, however for optimum reliability the resistor value
should be set as high as possible. The value is calculated as follows; with the maximum practical value
of 30 ohms.
RLIM = .IL7I M
COMMON MODE INPUT RANGE
Operational amplifiers are usually designed to have a common mode input voltage range that approximates the
power supply voltage range. However, to keep the cost as low as possible and still meet the requirements of most
applications the common mode input voltage range of the PA94 is restricted. The input pins must always be a least
30V from either supply voltage but never more than 450V. This means that the PA94 cannot be used in applications
where the supply voltages are extremely unbalanced. For example, supply voltages of +800V and –100V would not
be allowed in an application where the non-inverting pin is grounded because in normal operation both input pins
would be at 0V and the difference voltage between the positive supply and the input pins would be 800V. In this
kind of application, however, supply voltages +450V and -100V does meet the input common mode voltage range
requirements since the maximum difference voltage between the inputs pins and the supply voltage is 450V (the
maximum allowed). The output has no such restrictions on its voltage swing. The output can swing within 24V of
either supply voltage regardless of value so long as the total supply voltage does not exceed 900V.
PA94U
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