xtr111 noise/slew rate follow-up testing
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XTR111 Noise/Slew RateFollow-up Testing
Ian Williams
2/23/11
Background
• “Customer X” desires the following performance:– ≤ 100µs slew from 10%-90%– ≤ 5mVp (10mVpp) AC noise – No RC filter required at load
• Multiple transmitter-side capacitor values were tested to determine if this is possible
Test Circuit
• Changing R8 alters the output current/voltage, so only C3 was varied in these tests• Capacitance values tested: 50nF, 60nF, 70nF, 77nF, 94nF
50-94nF
Slew Rate Test #1C3 = 50nF (5*10nF)
• 10% to 90% slew time: 72µs
Noise Test #1C3 = 50nF (5*10nF)
• AC noise: 20.21mVpp
Slew Rate Test #2C3 = 60nF (6*10nF)
• 10% to 90% slew time: 82µs
Noise Test #2C3 = 60nF (6*10nF)
• AC noise: 18.00mVpp
Slew Rate Test #3C3 = 70nF (7*10nF)
• 10% to 90% slew time: 92µs
Noise Test #3C3 = 70nF (7*10nF)
• AC noise: 16.59mVpp
Slew Rate Test #4C3 = 77nF (47nF + 3*10nF)
• 10% to 90% slew time: 100µs
Noise Test #4C3 = 77nF (47nF + 3*10nF)
• AC noise: 15.99mVpp
Slew Rate Test #5C3 = 94nF (2*47nF)
• 10% to 90% slew time: 123µs
Noise Test #5C3 = 94nF (2*47nF)
• AC noise: 13.47mVpp
Conclusion
• Using C3 = 77nF provided the best noise performance (8mVp) while still meeting the 100µs 10% to 90% slew requirement
• If the slew rate requirement is relaxed slightly, the 5mVp noise requirement can be met with a larger C3 value
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