APA2171 Datasheet, PDF (13/21 Pages) Anpec Electronics Coropration – Stereo, Differential Input Cap-Free Line Driver

APA2171
Function Description
Line Driver Operation
V_OUT
Conventional Line Driver
V_OUT
V_DD
V_DD/2
GND
V_DD
GND
Shutdown Function
In order to reduce power consumption while not in use,
the APA2171 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 APA2171. 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 for the APA2171 is in shutdown mode.
DD
In normal operating, the APA2171’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.
V_SS
Cap-free Line Driver
Figure 1. Cap-free Operation
The APA2171’s line drivers use a charge pump to invert
the positive power supply (V_DD) to negative power supply
(V_SS), see figure1. The headphone drivers operate at this
bipolar power supply (V_DD and V_SS) 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 APA2171. 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 125^OC. The thermal protection is designed with a
25^OC hysteresis to lower the average T_J during continu-
ous thermal overload conditions, increasing lifetime of
the ICs.
Under-Voltage Protection
External under voltage detection can be used to shut-
down the APA2171 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 = (1.25-6µAxR3) x (R1+R2)/R2
Hysteresis = 5µA x R3 x (R1+R2)/R2
With the condition: R3>>R1//R2
For example, to obtain V_UVP=3.8V and 1V hysteresis, R1=
3kΩ, R2=1kΩ and R3=50kΩ.
Vsystem
R1
3kΩ
R2
1kΩ
R3
50kΩ
6µA
UVP Pin
1.25V
Figure 2. Under-Voltage Protection
Copyright © ANPEC Electronics Corp.
13
Rev. A.4 - Aug., 2013
www.anpec.com.tw