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LTC1323 Datasheet(PDF) 11 Page - Linear Technology |
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LTC1323 Datasheet(HTML) 11 Page - Linear Technology |
11 / 12 page 11 LTC1323 Driving an External Load from VEE An external load may be connected between ground and the VEE pin as shown in Figure 15. The LTC1323 VEE pin will sink up to a maximum of 10mA while maintaining the pin voltage between – 4.5V and – 5.5V. If an external load is connected, the VEE bypass capacitor should be in- creased to 4.7 µF. Both LTC1323 and the external chip should have separate VCC bypass capacitors but can share the VEE capacitor. EMI Filter Most LocalTalk applications use an electromagnetic inter- ference (EMI) filter consisting of a resistor-capacitor T network between each driver and receiver and the connec- tor. Unfortunately, the resistors significantly attenuate the drivers output signals before they reach the cable. Because APPLICATIO S I FOR ATIO the LTC1323 uses a single supply differential driver, the resistor values should be reduced to 5 Ω to 10Ω to guaran- tee adequate voltage swing on the cable (Figure 16a). In most applications, removing the resistors completely does not cause an increase in EMI as long as a shielded connec- tor and cable are used (Figure 16b). With the resistors removed the only DC load is the primary resistance of the LocalTalk transformer. This will increase the DC standby current when the driver outputs are active, but does not adversely affect the drivers because they can handle a direct indefinite short circuits without damage. Trans- former primary resistance should be above 15 Ωtokeepthe LTC1323 operating normally and prevent it from entering thermal shutdown. For maximum swing and EMI immu- nity, a ferrite bead and capacitor T network can be used (Figure 16c). Figure 16. EMI Filters EXTERNAL CHIP VCC VEE IVEE GND 12 24 21 1 µF 4.7 µF LTC1323 • F15 –5.5V ≤ VEE ≤ –4.5V IVEE ≤ 10mA 13 LTC1323 VCC = 5V C1 + Figure 15 TX 15 16 0.33 µF 14 13 12 11 10 9 8 1 2 5 6 7 3 4 CHARGE PUMP LTC1323CS 5V LocalTalk TRANSFORMER RX 100pF 100pF 120 Ω 100pF 100pF LTC1323 • TA02 0.33 µF SHDN DATA IN TX ENABLE RX ENABLE DATA OUT 1 µF 1 µF + Typical LocalTalk Connection TYPICAL APPLICATIONS N 5 Ω TO 10Ω 5 Ω TO 10Ω (a) (b) (c) 100pF FERRITE BEAD FERRITE BEAD 100pF LTC1323 • F16 100pF Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. |
Similar Part No. - LTC1323_15 |
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Similar Description - LTC1323_15 |
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