AS1749-BTDR 查看數據表（PDF） - austriamicrosystems AG

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AS1749-BTDR

Low-Voltage, Dual SPDT, Audio Clickless Switches with Negative Rail Capability

austriamicrosystems AG 

AS1747, AS1748, AS1749, AS1750

Datasheet - Detailed Description

8 Detailed Description

The AS1747– AS1750 are operating from a +1.8V to +5.5V supply and feature a negative signal capability that allows

signals below ground to pass through without distortion. A break-before-make switching and a low on-resistance are

also included in this analog dual SPDT switches. The device is fully specified for a 3.0V application.

A headphone or mute detection is included in the AS1748 and AS1750. This function is realized with a comparator

which has an internally generated thresh-hold of about 1/3 of VCC. To reduce click-and-pop sounds when switching

between precharged points the AS1749 and AS1750 have an internal shunt switch. This shunt switch automatically

discharges any capacitance at the NO and NC connection points.

9 Application Information valid Digital Control Inputs

The logic inputs of the AS1747– AS1750 accept up to +5.5V independent of the supply voltage. Due to this a mixing of

ill the logic levels in a system is possible. For example, with a +3.3V supply, IN_ can be driven low to GND and high to

+5.5V. For a +1.8V supply voltage, the logic levels are 0.5V (low) and 1.4V (high); for a +5V supply voltage, the logic

levels are 0.8V (low) and 2.0V (high).

t Analog Signal Levels

G s The change of the on-resistance of the AS1747– AS1750 is very little for analog input signals over the whole supply

voltage range. The switches are bi-directional, so the NO_, NC_, and COM_ pins can be either inputs or outputs.

A t The AS1747– AS1750 pass signals as low as VCC - 5.5V, including signals below ground with minimal distortion.

s n Comparator (AS17481/AS1750)

e To implement a mute and headphone function, a comparator is included in the AS1748 and AS1750. The negative ter-

m t minal of this comparator is connected to the outside (via pin CMP-) while the positive terminal is internally set to VCC/3.

The output of the comparator (CMPO) is logic high when the negative terminal (CMP-) is below the threshold. CMPO is

a n logic low when CMP- is higher than VCC/3.

Headphone audio signals are typical biased to VCC/2 so a comparator threshold of VCC/3 is sufficient for the head-

o phone detection.

c Shunt Switch (AS17491/AS1750)

l Due to the switching between audio sources, audible click-and-pop sounds occur. To reduce this sounds a 100Ω shunt

switch is implemented in the AS1749 and AS1750. This shunt switch automatically discharges any capacitance at the

a NC_ or NO_ terminals when they are unconnected to COM_.

ic Audible clicks and pops are caused when a step DC voltage is switched into the speaker. By automatically discharging

the side that is not connected, any residual DC voltage is removed, thereby reducing the clicks and pops.

n Power-Supply Sequencing and Overvoltage Protection

h Caution: Stresses beyond the listed absolute maximum ratings in Table 3 on page 4 may cause permanent damage

to the device. Exposure to absolute maximum rating conditions for extended periods may affect device

creliability.

Proper power-supply sequencing is recommended for all CMOS devices. Always apply VCC before applying analog

Te signals, especially if the analog signal is not current-limited.

1. on request

www.austriamicrosystems.com/Analog-Switches/AS1747-50 Revision 1.02

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