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DM74ALS5245N 数据表(PDF) 4 Page - Fairchild Semiconductor |
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DM74ALS5245N 数据表(HTML) 4 Page - Fairchild Semiconductor |
4 / 7 page www.fairchildsemi.com 4 ALS Noise Characteristics The setup of a noise characteristics measurement is critical to the accuracy and repeatability of the tests. The following is a brief description of the setup used to measure the noise characteristics of ALS. Equipment: Word Generator Printed Circuit Board Test Fixture Dual Trace Oscilloscope Procedure: 1. Verify Test Fixture Loading: Standard Load 50 pF, 500 Ω. 2. Deskew the word generator so that no two channels have greater than 150 ps skew between them. This requires that the oscilloscope be deskewed first. Swap out the channels that have more than 150 ps of skew until all channels being used are within 150 ps. It is important to deskew the word generator channels before testing. This will ensure that the outputs switch simultaneously. 3. Terminate all inputs and outputs to ensure proper load- ing of the outputs and that the input levels are at the correct voltage. 4. Set VCC to 5.0V. 5. Set the word generator to toggle all but one output at a frequency of 1 MHz. Greater frequencies will increase DUT heating and affect the results of the measure- ment. 6. Set the word generator input levels at 0V LOW and 3V HIGH. Verify levels with a digital volt meter. FIGURE 1. Quiet Output Noise Voltage Waveforms Note 5: VOHV and VOHP are measured with respect to VOH reference. VOLV and VOLP are measured with respect to ground reference. Note 6: Input pulses have the following characteristics: f = 1 MHz, t r = 3ns, tf = 3 ns, skew < 150 ps. VOLP/VOLV and VOHP/VOHV: • Determine the quiet output pin that demonstrates the greatest noise levels. The worst case pin will usually be the furthest from the ground pin. Monitor the output volt- ages using a 50 Ω coaxial cable plugged into a standard SMB type connector on the test fixture. Do not use an active FET probe. • Measure VOLP and VOLV on the quiet output during the HL transition. Measure VOHP and VOHV on the quiet out- put during the LH transition. • Verify that the GND reference recorded on the oscillo- scope has not drifted to ensure the accuracy and repeat- ability of the measurements. VILD and VIHD: • Monitor one of the switching outputs using a 50 Ω coaxial cable plugged into a standard SMB type connector on the test fixture. Do not use an active FET probe. • First increase the input LOW voltage level, VIL, until the output begins to oscillate. Oscillation is defined as noise on the output LOW level that exceeds VIL limits, or on output HIGH levels that exceed VIH limits. The input LOW voltage level at which oscillation occurs is defined as VILD. • Next decrease the input HIGH voltage level on the word generator, VIH until the output begins to oscillate. Oscil- lation is defined as noise on the output LOW level that exceeds VIL limits, or on output HIGH levels that exceed VIH limits. The input HIGH voltage level at which oscilla- tion occurs is defined as VIHD. • Verify that the GND reference recorded on the oscillo- scope has not drifted to ensure the accuracy and repeat- ability of the measurements. FIGURE 2. Simultaneous Switching Test Circuit |
类似零件编号 - DM74ALS5245N |
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类似说明 - DM74ALS5245N |
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