APA2181 datasheet(14/21 Pages) ANPEC

14 / 21 page

Rev. A.2 - Apr., 2010

APA2181

www.anpec.com.tw

Headphone Driver Operation

Function Description

The APA2181’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 APA2181. 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 APA2181 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 APA2181. The trigger point between a

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

mended to switch between ground and the supply volt-

age 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 APA2181 is in shutdown mode.

In normal operating, the APA2181’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 definite voltage

to avoid unwanted circumstance changes.

DD/2

GND

OUT

GND

OUT

Conventional Headphone Driver

Cap-free Headphone Driver

Low Drop-Out (LDO) Regulator

The LDO regulator’s output provides maximum 5mA drive

capacity for external audio codec. A 1

µF decoupling ca-

pacitor with 0.1

µF capacitor (filtering the high frequency

noise) is recommended at LDO regulator’s output. The

LDO monitors the output current and limits the maximum

output current to prevent damages during current over-

load or short circuit conditions.

The LDO provides a soft-start function, using the con-

stant current to charge the output capacitor that gives a

rapid and linear output voltage rise. If the load current is

above the current limit start-up, the LDO cannot start

successfully.

APA2181 Datasheet(PDF) 14 Page - Anpec Electronics Coropration

APA2181 Datasheet(HTML) 14 Page - Anpec Electronics Coropration

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Datasheet Download

Link URL