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ISL54065_0911 Arkusz danych(PDF) 10 Page - Intersil Corporation |
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ISL54065_0911 Arkusz danych(HTML) 10 Page - Intersil Corporation |
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10 / 15 page  10 FN6583.2 November 3, 2009 on/off transients are AC coupled by the 220µF capacitor to the speaker load causing a click and pop noise. The ISL54065 has shunt switches on the NO and NC pins to eliminate click and pop transients (see Figure 10). These switches are driven complimentary to the main switch. When NC is connected to COM, the shunt switch is active on the NO pin (and vice versa). The shunt switches connect an impedance (140 Ω typical, see Figure 25) from the NO/NC pin to ground to discharge any transients that may appear on the NO or NC pins. When the DC bias becomes active at the source, the NO and NC terminals will also have a DC offset due to capacitor dv/dt principle. The DC offset will be discharged through the shunt impedance on the NO and NC terminals instead of the speaker, eliminating click and pop noise. On the ISL54065, the Click and Pop Circuitry is enabled when the CP pin is logic high (>1.4V). The Click and Pop Circuitry may be disabled by tying the CP pin low (<0.4V). *Under high impedance loads (20k Ω) such as the input impedance of pre-amplifiers, the COM terminal voltage may rise due to small leakage currents charging the COM capacitance. This is not seen when low impedance (32 Ω) loads such as headphones are used because the small leakage currents does not result in significant potential drop across the load. If the user desires to reduce the voltage build up on the COM pin, a 1k Ω to ground may be placed on the COM pin. This impedance is small enough to reduce the voltage build up significantly while not increasing the power dissipation dramatically. Current consumption considerations will need to be taken for driving a smaller load impedance under this scenario. Click and Pop with Enable Pin Click and pop elimination can be driven with the Enable pin by setting it low. Having the Enable pin low turns OFF the main switches (NO and NC) while the Click and Pop Circuitry will be active. Transient voltages due to power on/off from both sources will be shunted to ground. For proper Click and Pop Elimination the Enable pin should be driven high at least 200ms after any source transients occurs to avoid audible transients at the speaker load. Click and Pop with Input Select Pin Click and pop elimination can also be driven with the Input Select pin. When INx = 0, the NOx terminals are connected to the shunt impedance. When INx = 1, the NCx terminals are connected to the shunt impedance. In this situation, only one of the source transient voltages will be shunted to ground, depending on the Input Select state. The Input Select pin should be driven 200ms after any source transients occurs to prevent audible transients at the speaker load. Logic-Level Thresholds This switch family is 1.8V CMOS compatible (0.45V VOLMAX and 1.35V VOHMIN) over a supply range of 1.8V to 3.3V (see Figure 16). At 3.3V the VIL level is 0.5V maximum. This is still below the 1.8V CMOS guaranteed low output maximum level of 0.45V, but noise margin is reduced. At 3.3V the VIH level is 1.4V minimum. While this is above the 1.8V CMOS guaranteed high output minimum of 1.35V under most operating conditions the switch will recognize this as a valid logic high. The digital input stages draws a larger supply current whenever the digital input voltage is not at one of the supply rails. Driving the digital input signals from GND to V+ with a fast transition time minimizes power dissipation. The ISL54065 has been designed to minimize the supply current whenever the digital input voltage is not driven to the supply rails (0V to V+). For example driving the device with 2.85V logic high while operating with a 4.2V supply the device draws only 1µA of current. High-Frequency Performance In 50 Ω systems, the ISL54065 has an ON switch -3dB bandwidth of 60MHz (see Figure 21). The frequency response is very consistent over a wide V+ range, and for varying analog signal levels. An OFF switch acts like a capacitor across the open terminals and AC couples higher frequencies, resulting in signal feed-through from a switch’s input to its output. Off-Isolation is the resistance to this feed-through. Crosstalk indicates the amount of feed-through from one switch channel to another switch channel. Figure 22 details the high Off-Isolation and Crosstalk rejection provided by this part. At 100kHz, Off-Isolation is about 60dB in 50 Ω systems, decreasing approximately 20dB per decade as frequency IN COM RL 220µF 32 Ω NO NC V+ GND C AUDIO SOURCE A 220µF RSH AUDIO SOURCE B RSH µP CP EN ISL54065 FIGURE 10. CLICK AND POP OPERATION ISL54065 |
Podobny numer części - ISL54065_0911 |
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Podobny opis - ISL54065_0911 |
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