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FAN6555 Fiches technique(PDF) 5 Page - Fairchild Semiconductor |
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FAN6555 Fiches technique(HTML) 5 Page - Fairchild Semiconductor |
5 / 12 page PRODUCT SPECIFICATION FAN6555 REV. 1.1.3 8/4/03 5 Applications Using the FAN6555 for DDR Bus Termination The circuit schematic in Figure 1 shows a recommended approach for constructing a bus terminating solution for a DDR bus. This circuit can be used in PC memory and Graph- ics memory applications as shown in Figures 3 and 4. Note that the FAN6555 can provide the voltage reference (VREF) and terminating voltages (VTT). Using the layout as shown in Figures 5, 6, and 7, and measuring the VTT performance using the test setup as described in Figure 8, the FAN6555 delivered a VTT ± 20mV for 1A to 2A loads (see Figure 9). Table 1 provides a recommended parts list. An alternate application circuit for the FAN6555 is shown in Figure 2. The number of external components is reduced compared to the circuit in Figure 1. This is achieved by replacing four, 0.1µF bypass capacitors with one, low ESR, 10µF ceramic capacitor placed right next to U1. Two 100 Ω resistors are also eliminated. High value, surface-mount MLC capacitors were not available when the original appli- cation circuit (Figure 1) was developed. Both application circuits offer the same electrical performance but the circuit shown in Figure 2 has a reduced bill-of-materials. Table 2 shows the recommended parts list for the circuit of Figure 2. Bus Termination Solutions for Others Buses Table 3 provides a summary of various bus termination VREF & VTT requirements. The FAN6555 can be used for those applications. Figure 2. Alternate Application Circuit 16 15 14 13 12 11 10 9 U1 FAN6555 VDD PVDD1 VL1 PGND1 PGND2 VL2 PVDD2 DGND AVCC VCCQ VREFOUT AGND SHDN VREFIN VFB VDD 1 2 3 4 5 6 7 8 R3 100k Ω VCCQ VREFOUT VTT 2.5V TO 4V SHDN VREFIN GND GND TO SDRAMS C4 1nF C5 470 µF R1 100k Ω R2 1k Ω C2 0.1 µF C1 820 µF F2V OS-CON L1 3.3 µH C3 10 µF |
Numéro de pièce similaire - FAN6555 |
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Description similaire - FAN6555 |
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