APA2172 datasheet(14/22 Pages) ANPEC

14 / 22 page

Rev. A.8 - Aug., 2013

www.anpec.com.tw

APA2172

Function Description

Line Driver Operation

Figure 1. Cap-free Operation

The APA2172’s line drivers use a charge pump to invert

the positive power supply (V

DD) to negative power supply

SS), see figure1. The headphone drivers operate at this

bipolar power supply (V

DD and VSS) and the outputs refer-

ence refers to the ground. This feature eliminates 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 al-

most doubled.

Thermal Protection

The thermal protection circuit limits the junction tempera-

ture of the APA2172. 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 APA2172 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 APA2172. 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 APA2172 is in shutdown mode.

In normal operating, the APA2172’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.

Under-Voltage Protection

External under voltage detection can be used to shut-

down the APA2172 before an input device can generate a

pop. The shutdown threshold at the UVP pin is 1.25V.

The user selects a resistor divider to obtain the shut-

down threshold and hysteresis for the specific application.

The thresholds can be determined as below:

VUVP = (1.25-6

µAxR3) x (R1+R2)/R2

Hysteresis = 5

µA x R3 x (R1+R2)/R2

With the condition: R3>>R1//R2

For example, to obtain V

UVP=3.8V and 1V hysteresis, R1=

Ω, R2=1kΩ and R3=50kΩ.

Figure 2. Under-Voltage Protection

Vsystem

Ω

50k

Ω

UVP Pin

1.25V

µA

DD/2

GND

OUT

GND

OUT

Conventional Line Driver

Cap-free Line Driver

APA2172 Datasheet(PDF) 14 Page - Anpec Electronics Coropration

APA2172 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 22

Datasheet Download

Link URL