APA2178 datasheet(23/30 Pages) ANPEC

23 / 30 page

Rev. A.3 - Jul., 2009

www.anpec.com.tw

APA2178

voltage PV

DD to provide maximum device performance.

By switching the both RSD and LSD pins to low level, the

amplifier enters a low-consumption current circumstance,

with charge pump disabled, and very small I

DD for the

APA2178. The charge pump is enabled once either RSD

or LSD pin is pulled to high. In normal operating, the

APA2178 RSD and LSD pins should be pulled to high

level to keep the IC out of the shutdown mode. The RSD

and LSD pins should be tied to a definite voltage to avoid

unwanted mode changing.

Function Description

Figure 1. Cap-free Operation

The APA2178 headphone drivers use a charge pump to

invert the positive power supply (PV

DD) to negative power

supply (CV

SS), see figure 1. 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 capacitors which are used in conven-

tional single-ended headphone amplifiers. Compared

with the single power supply amplifiers, the power sup-

ply voltage is almost double.

The APA2178 is a stereo, fixed gain, and cap-free head-

phone driver. The gain is set by internal resistors, input

resistors (R

i), and feedback resistors (Rf) with -1.5V/V

(See Typical Application Circuit).

Shutdown Function

In order to reduce power consumption, the APA2178 con-

tains two shutdown signal input pins (LSD for left chan-

nel and RSD for right channel) to allow the respective

shutdown which turns off the bias current of the amplifier.

This shutdown feature turns the amplifier off when logic

low is placed on the RSD or LSD pin for the APA2178.

The trigger point between a logic high and a logic low

level is typically 0.6V

DD and 0.3VDD. It is highly recom-

mended to switch between the ground and the supply

DD/2

GND

OUT

GND

OUT

Conventional Headphone amplifier

Cap-free Headphone amplifier

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