APA2180 datasheet(13/22 Pages) ANPEC

13 / 22 page

Rev. A.3 - Dec., 2012

APA2180

www.anpec.com.tw

Headphone Driver Operation

Function Description

The APA2180’s headphone drivers use a charge pump

to invert the positive power supply (V

DD) to negative power

supply (V

SS), see figure1. The headphone drivers oper-

ate at this bipolar power supply (V

DD and VSS) and the out-

puts reference refers to the ground. This feature elimi-

nates the output capacitor that is using in conventional

single-ended headphone drive amplifier. Compare with

the single power supply amplifier, the power supply range

has almost doubled.

Figure 1. Cap-free Operation

Thermal Protection

The thermal protection circuit limits the junction tempera-

ture of the APA2180. When the junction temperature ex-

ceeds T

J = +150

oC, a thermal sensor turns off the driver,

allowing the devices to cool. The thermal sensor allows

the driver to start-up after the junction temperature down

about 125oC. The thermal protection is designed with a

25oC hysteresis to lower the average T

J during continu-

ous thermal overload conditions, increasing lifetime of

the ICs.

Shutdown Function

In order to reduce power consumption while not in use,

the APA2180 contains shutdown controllers to externally

turn off the amplifier bias circuitry. This shutdown feature

turns the amplifier off when logic low is placed on the

SDN pins for the APA2180. The trigger point between a

logic high level is 1.0V and logic low level is 0.35V. It is

recommended to switch between the ground and the sup-

ply voltage V

DD to provide maximum device performance.

By switching the SDN pins to a low level, the amplifier

enters a low-consumption current circumstance, charge

pump is disabled, and I

DD for the APA2180 is in shutdown

mode. In normal operating, the APA2180’s SDN pins

should be pulled to a high level to keep the IC out of the

shutdown mode. The SDN pins should be tied to a defi-

nite voltage to avoid unwanted circumstance changes.

DD/2

GND

OUT

GND

OUT

Conventional Headphone Driver

Cap-free Headphone Driver

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