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[FAQ] General Design Tips and Useful Information

Adam Sidelsky
Guru 66550 points

Other Parts Discussed in Thread: TPA711, TAS5630, TAS5615, TAS5613

Class AB amplifier efficiency in SE configuration

Q: Class AB amplifier efficiency in SE configuration

A customer wants to use a TPA711 in SE mode to drive a 15 Ohm speaker. Could you provide some design equations for calculating the efficiency of the audio amp and also the average current drawn so that i can calculate the amplifier dissipation. There is a detailed calculation for BTL in the datasheets.


A: Re: Class AB amplifier efficiency in SE configuration

The equations for efficiency for BTL and SE are the same except for the IDDrms calculation. For SE, IDDrms = Vp/(pi*RL) or half the value for BTL. This will make the amplifier twice as efficient as BTL for the same output power. Keep in mind these equations are only valid for sine waves and they assume the user has gotten rid of the DC current that will be flowing in single ended configuration. This can be done by using a DC blocking cap or tying the other end of the speaker to Vdd/2 instead of ground.

If this DC current is not removed, then an additional power dissipation of Vdd^2/RL will be occur, which will cause a drop in the efficiency of the system.

Consumer Devices in Industrial Applications

Q: TAS5630 ambient temp

Hello,

I would like to use the TAS5630 for an industrial application.

What will happe if i use it in an environment with an ambiante tempeature higher than 70°C (Reduce the MTBF, malfunction, reduce the performance?)

Is it expected in the future an  industrial range for this type of component?

Thanks


A: Re: TAS5630 ambient temp

Officially, the manufacturer (TI) does not guarantee ANY device specs or even device operation outside of the noted operating temperature range.

However, many consumer devices will operate just fine under typical 'industrial' ambient operating conditions. Specs that typically change at high temperatures include increased noise and worse power vs. thd performance.  Also, the device may go into thermal protection when outputting "normal" power levels.  For abnormal operating conditions it is best to test the specs that are important to your system at the extreme conditions.

One point that is hard to test, but is a very legitimate concern is long term device operation.  If a device is consistently operated outside of the specified conditions, long term reliability may suffer (i.e. the device may fail well before the expected lifetime is up).  Again, this goes back to the point that the manufacturer does not guarantee operation outside of the specified range.

Finding a device's weight (mass)

All devices released to production and orderable on ti.com will have this info.  Please look in the device's product folder on ti.com. 

  1. Go to Quality & Environmental Data
  2. Select View under Details column for the device
  3. Scroll to the right under Package Details
  4. Look for Device Mass.

General Suggestions on TDMA Noise in portable products

TDMA noise is a problem in many portable and office audio products. This discussion is taken from a correspondence with a customer, and it contains a few general recommendations on how to improve TDMA noise in a general audio application. This particular application is for a subsystem - an amplifier with both headphone (HP) and speaker (class-D) outputs integrated into a single package. Please feel free to add comments or suggested troubleshooting methods to this discussion post.
The first step in TDMA noise troubleshooting is figuring out how the noise is getting into the system. There are three common injection/coupling paths to check regarding TDMA noise:
Inputs
The TDMA noise could be coupling into the system along the input traces leading to the amplifier device. To check this, try disconnecting the amplifier's input capacitors from the PCB and AC GND the inputs of thedevice (AC GND the input pins as close to the device as possible). If the TDMA noise goes away, then the noise is likely coupling onto the inputs and transmitting through the amplifier.
In this case, ensure that the input traces are buried under a GND plane. Also, ensure that the shielding for the audio portion of the product is independent of the antenna and RF portions of the phone (or receiver). Finally, make sure that the input traces are not crossing or overlapping with any other board level traces that could carry the TDMA noise – particularly supply traces or RF traces.
Headphone only OR class D only
If the TDMA noise is heard on the HP only or the class D only, it is likely that the inputs to the amplifier are not to blame. In this case the noise could be getting into the system by either directly coupling onto the output traces, or by coupling onto a power supply line that only connects to the HP or class D of the amplifier.
In this case, ensure that the output traces of the affected output are buried under a GND plane if possible, and that they are not exposed to any RF traces. Also, see if the noise can be improved by increasing the value of decoupling capacitors for the supply lines to the affected output (such as HPVDD, or VBatt – assuming these are supplied via separate references).
Regarding the decoupling capacitors, please ensure that all decoupling caps are connected to the top GND layer. Sometimes capacitors are grounded to an inner layer using vias. This is not recommended as it can increase the AC impedance between supply and ground, which can make TDMA noise issues worse.
Headphone AND class D (but not input traces)
If the TDMA noise is present on both the HP and class D amp, but does not seem to be injected through the input traces, check the supply references that are used by both systems (primarily, check Vbatt. Try improving the decoupling on this line by increasing the value of the decoupling cap, and ensure that it is well grounded in the system). If this third situation is the case, the signal could also be coupling onto both sets of output traces, or onto the inputs after the input capacitors (not likely – but possible). Try shielding these areas from the antenna and see if the noise goes away.
Lastly, related to all of these points, check how the amplifier's GND balls are connected to the system. The best performance TDMA noise performance is usually achieved by connecting the GND ball(s) to both the inner GND layers and to the top GND layer. This provides the lowest impedance AC path from the supply lines to system GND, and should improve TDMA noise in almost all cases.

Guideline for fixing heat sink on PHD, DKD, and DDV packages

Guideline for fixing heat sink

Q: Do you have any spec or guideline for max torque for fixing heat sink on TAS5615/5630PHD?

A: There is no easy answer to this question as it depends on several system-level variables.

In general, we recommend using a thin layer of non-conductive, thermally-conductive heat sink grease. The layer should be extremely thin, the goal is to fill any tiny gaps between the device pad and the heat sink. The thermal conductance of the heat sink grease is >> metal to metal contact, so try to limit the thickness of the heat sink grease used to maximize the thermal performance of your system.

Secondly, be careful that you do not warp your board, especially when using one heat sink for multiple devices. You want to torque the screws in an order that does not cause board warping. If there is board warping due to poor sequence or uneven torquing of the screws, you will hurt the thermal performance of your system.

We also recommend tapping the heat sink and using machine screws to connect it. If you use self-tapping screws, you run the risk of introducing shards of metal in your system which could result in a short in your system.

Finally, be careful with your stencil thickness and stand-off height. Ideally, you don't want to stress the pins as they enter the package as this could result in broken pins over the lifetime of your product.

The max loads are 

PHD and DDV - max load is 90 Newtons 
DKD - max load is 200 Newtons

Measuring the impedance of a loudspeaker

Surfing thru the forum, you'll see many threads related to short-circuit protection and over-current protection problems. These are usually caused by one of two things: 1) a poor output filter design, or 2) an unknown dip in speaker impedance. 

For #2, if you use a DMM to measure the speaker impedance, you only get part of the picture - DC. Since a speaker is comprised of a complex impedance, you really need to measure it across frequency. 

You might find this article very helpful then:
http://ap.com/kb/show/12 this is the knowledge base article that explains how to measure complex impedances using the AP. You may have to register (free account) on the AP sight, but worth it as they have quite a few articles there.
There is a really good overview (actually, almost covers the whole thing) written from the perspective of measuring a loudspeaker here: http://www.ap.com/kb/show/187#sound just scroll halfway down the page until you get to the “Sound Advice” heading.

Automatic Loudspeaker Equalizer Software

ALE 5.2.zip

Need a .bxl file generated?

A .bxl file is a "Binary XLator" file which is intended to be a universal footprint for any layout program. ADI has an app note which describes it.

Usually, these are stored in the Product Folder in the web under the "Quality & packaging" tab and then "CAD/CAE symbols."

If the file is not posted there, you will need to request a new one be generated (please make sure it then gets posted to the Product Folder for other customers!):

Submit a model request at http://webenchmodeling/ModelRequestSurvey.aspx.  Select the Altium symbol/footprint category, and in the Comments section state that this is a .bxl request.

Quick Reference guide to Max output power of a Class D amplifier

Q: Quick Reference guide to Max output power of a Class D amplifier

Can you comment on a Class D's max output power for a given power supply and load?

A: Re: TAS5613 - max output power from 24V to 4ohm load?

Hi,

The pdf file attached at the end of this post shows how to approximate the max output power for a Class D at a given PVDD and load. It uses the TAS5613 as an example with PVDD = 24V and a 4 ohm load.

What the file shows is that the RDSON of the device creates a voltage divider with the load. It shows that the largest unclipped sine wave will have about 65W and a clipped signal (10% THD) will be 81.6. Note that the calculation of 10% THD is an approximation that says P_clipped = 1.25* P_unclipped.

If RdsOn were 0 ohm resistance (ideal output stage), the power would be 72W unclipped and 90W clipped.

2474.TAS5613 Max Power.pdf

Replacing NXP "End of Life" audio amps with TI devices

Replacing NXP "End of Life" audio amps with TI devices

We've been noticing a lot of requests for similar parts to replace the NXP devices that are being discontinued. I've made a comprehensive list for these NXP devices and their TI replacements below. Note: they are not pin-to-pin replacements; they are the most similar parts based off of architecture and output power.

NXP Part#

Most Similar TI Part

NE58633BS

TPA2001D1

SA58637BS

TPA2012D2

TDA8569Q

TPA3245

TDA8920BJ

TPA3255

TDA8920BTH

TPA3255

TDA8922BJ

TPA3116D2

TDA8922BTH

TPA3116D2

TDA8933BTW

TPA3136D2

TDA8948J

TPA3117D2

TFA9810T

TPA3136D2

TFA9812HN

TPA3117D2

TFA9815T

TPA3004D2

TFA9882AUK

TAS2552

TFA9892AUK

TAS2552

What is BTL configuration?

Problem:
What is BTL configuration? How is BTL different than SE?

 

 
Solution:
BTL is an acronym for "bridge-tied load." A bridge-tied load configuration consists of one amplifier driving one side of a load and another amplifier (with an inverted signal from the first amplifier) driving the other side of the load. This results in 2x more voltage swing across the load than you would have in a single-ended configuration where one side of the load is tied to an amplifier and the other side to ground. Twice the voltage swing across the load equates to 4x the power to the load (P = V^2/R). So, a BTL load configuration offers 4x more power to the load than a single ended configuration from the same supply voltage. Be aware, that BTL amplifiers dissipate 4x the heat of a Single-Ended amplfier under the same supply voltage and load conditions. Refer to the TPA7x1 series parts in the applications section for more on BTL. Also note that the output DC blocking capacitors are NOT required in the BTL configuration. Since the load is tied across two amplifiers with the same DC bias and the signal across the load is the difference between the amplifier outputs, the DC bias is removed.