MAX13301 datasheet(13/37 Pages) MAXIM

13 / 37 page

4-Channel, Automotive Class D Audio Amplifier

amplifier ramp. The design equation that must be met to

ensure constant frequency is as follows:

Error-Amplifier Ramp < 2/3 Triangle-Wave Ramp

The error-amplifier ramp is fixed by the gain of the dif-

ferential amplifiers used in the feedback loop and by

the error-amplifier compensation capacitor programmed

through I2C. To ensure the design equation for fixed fre-

quency is met, the error-amplifier compensation capaci-

tor tracks the integrator capacitor used to generate the

triangle wave.

For optimal noise shaping, the error-amplifier capaci-

tor should be set to a small value. This results in a

broadband spectrum where the error amplifier pushes

the noise created by the clock jitter and PWM sam-

pling above the audio range. However, there is a limit.

Because the triangle-wave capacitor tracks the error-

amplifier capacitor, small capacitor values can clip

the triangle wave as it runs out of supply. This effect is

aggravated at high PVDD voltages by the ADC action

that decreases the integrator resistor at higher supply

voltages. Tables 20 and 21 are lookup tables to facili-

tate choosing the optimal setting for the error-amplifier

capacitance (MAP.COMP[2:0]).

It is possible to change this setting instantaneously while

playing music, but if there is no music, a slight audible

click is heard at the speakers. Systems that monitor

the input voltage can take advantage of this instanta-

neous programmability and use a smaller error-amplifier

capacitor at lower PVDD voltages. Higher switching

frequencies also allow the use of a smaller integrator

capacitor, and thus help improve the noise performance

of the amplifier.

Do not set the error-amplifier capacitor to a value less

than 18pF. Doing so results in extreme distortion, as the

triangle wave clips. The MAP.COMP[2:0] settings that

result in this behavior are listed as reserved (Table 19).

Advantage of Feedback After the Filter

High-fidelity audio amplifiers require very low output

impedance. The device achieves this by using a dual-

feedback approach. The digital feedback (feedback

from OUT__ outputs) emulates current-mode enabling on

chip compensation. The analog feedback (FB__ inputs)

significantly reduces the output impedance of the ampli-

fier and at the same time, compensates for the nonideal

characteristics of the output filter. If the characteristics

of the speaker and/or output filter change with age or

temperature, the analog feedback compensates accord-

ingly. Further inductor matching is less critical because

the inductors are inside the feedback loop. Because the

inductors are inside the feedback loop, the loop can

dampen out any LC ringing that might occur when the

amplifier is used as a line driver. The analog feedback is

differential so it does not help with common-mode ring-

ing. Thus, the Zobel (RC) networks are required on each

speaker connection to damp any common-mode ringing

associated with the LC output filter and speaker.

Operating Modes

Configure the device for one of three states of activity:

normal, standby, or shutdown.

Normal

In normal mode, the device is ready for play. Placing

the device in standby reduces power consumption while

keeping fault monitors and the I2C interface on to com-

municate fault conditions. In shutdown, the device is

completely disabled and draws minimal current from the

battery.

To reset the device and clear all register contents to their

reset values, set CTRL5.RST to 1. After reset, this bit is

automatically cleared back to 0.

Standby

In standby, all circuitry is disabled except the fault moni-

tors and the I2C interface. The I2C registers retain their

content and are still interactive. To place the device in

standby, set the CTRL2.STBY bit to 1. In standby, the

device draws 11mA from all power-supply inputs.

Before exiting standby, always set the CTRL1.CL_TH (cur-

rent-limit threshold setting) bit to 1. After exiting standby,

clear CTRL1.CL_TH back to 0.

Table_1._Operating_Modes

X = Don’t care

MODE

CTRL2.STBY

I2C

FAULT_MONITORS

ALL_OTHER_CIRCUITRY

Normal

High

Enabled

Standby

High

Enabled

Off

Shutdown

Low

Off

MAX13301 Datasheet(PDF) 13 Page - Maxim Integrated Products

MAX13301 Datasheet(HTML) 13 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Datasheet Download

Link URL