Build Thread for TPA BIII + Ian Async I2S FIFO + OPC NTD1 + Salas SSLV - Page 29 - diyAudio
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Old 27th November 2012, 05:48 PM   #281
syklab is offline syklab  Hong Kong
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Quote:
Originally Posted by iancanada View Post
Hi bigpandahk,

Don't use that adapter, it was not designed for a power supply. I'll send you a couple of my TPS7A4700 PCBs for a try.

Ian
Hi Ian,
Anyway I can piggyback on bigpandahk to try the TPS7A4700?

Thanks
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Old 27th November 2012, 06:03 PM   #282
qusp is offline qusp  Australia
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you know there is a demo board for it direct from Ti right that you can buy and its already soldered? do you have tools for soldering this? you do realize its DFN package with a powerpad underneath so you NEED reflow oven or hotair tool to solder?

also I do wish people would not take advantage... he doesnt get this stuff for free, hes just really generous. fine if he puts feelers out for testers, but flat out asking... I dunno maybe you are asking to buy? in which case there are plenty of people ahead of you in the GB thread asking for when its ready

Last edited by qusp; 27th November 2012 at 06:06 PM.
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Old 27th November 2012, 07:04 PM   #283
AR2 is offline AR2  United States
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Quote:
Originally Posted by qusp View Post
you know there is a demo board for it direct from Ti right that you can buy and its already soldered? do you have tools for soldering this? you do realize its DFN package with a powerpad underneath so you NEED reflow oven or hotair tool to solder?

also I do wish people would not take advantage... he doesnt get this stuff for free, hes just really generous. fine if he puts feelers out for testers, but flat out asking... I dunno maybe you are asking to buy? in which case there are plenty of people ahead of you in the GB thread asking for when its ready
+1
Strongly agree. I hope many on this thread realize how advanced Ian's circuits are, and how fortunate we are to have a chance to play with this technology. The quality and speed he is designing is staggering, and on the top of that, maintaining pretty sizable group buys is amazing dedication. I think from one guy that is quite enough.
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Old 27th November 2012, 08:02 PM   #284
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Originally Posted by AR2 View Post
+1
Strongly agree. I hope many on this thread realize how advanced Ian's circuits are, and how fortunate we are to have a chance to play with this technology. The quality and speed he is designing is staggering, and on the top of that, maintaining pretty sizable group buys is amazing dedication. I think from one guy that is quite enough.
Quote:
Originally Posted by qusp View Post
you know there is a demo board for it direct from Ti right that you can buy and its already soldered? do you have tools for soldering this? you do realize its DFN package with a powerpad underneath so you NEED reflow oven or hotair tool to solder?

also I do wish people would not take advantage... he doesnt get this stuff for free, hes just really generous. fine if he puts feelers out for testers, but flat out asking... I dunno maybe you are asking to buy? in which case there are plenty of people ahead of you in the GB thread asking for when its ready
Thanks guys for your kind words. The pleasure you brought to me is more then what I did to you. Your feedbacks made my project meaningful.

Ian
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Old 27th November 2012, 11:04 PM   #285
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AR2, qusp and Ian, you are all great members in diyaudio and always give great advise and support to members. Without you guys, I don't think I can finish this complicated project.
Ian, thanks for your generous to offer me the PCB.
qusp : I considered to buy the Ti evaluation kit, it's much cheaper than buying components but the size is a little bigger than expected. So I bought the adaptor. Thanks for reminding me that the cap have to be close to the pins, I will finish the prototype with SMD cap and see if it will smoke

Last edited by bigpandahk; 27th November 2012 at 11:11 PM.
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Old 27th November 2012, 11:10 PM   #286
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If I were you I would have a read of the datasheet for power dissipation and look at the load currents that you're expecting. Consider that you're also driving LCD etc from arduino.

You should be able to calculate if you expect smoke or not

qusp, I think with Ian's pcb you might just be able to get to the power pad from underneath. Though it's surely not going to be an easy (I mean heating from underneath while keeping the chip straight?) or even a neat or reliable job without a rework station.


What are you using to supply the regulator anyway? Seems an odd choice for the non-critical parts of the circuit. Considering that the i2c will be isolated and the relays are ... well it just feels odd to drive the coil of a relay with something with performance like this.

Last edited by hochopeper; 27th November 2012 at 11:13 PM.
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Old 27th November 2012, 11:15 PM   #287
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Originally Posted by hochopeper View Post
If I were you I would have a read of the datasheet for power dissipation and look at the load currents that you're expecting. Consider that you're also driving LCD etc from arduino.

You should be able to calculate if you expect smoke or not

qusp, I think with Ian's pcb you might just be able to get to the power pad from underneath. Though it's surely not going to be an easy (I mean heating from underneath while keeping the chip straight?) or even a neat or reliable job without a rework station.
I've read the datasheet before and it recommend to use the copper on PCB as heat sink. I know the adaptor doesn't have enough copper for heatsink, I consider to attach a small heatsink on the chip to see if it help.
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Old 27th November 2012, 11:46 PM   #288
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Pd = (Vout-Vin) x Iout (datasheet formula 6)

Tjunction = Tambient * [(theta J-A) * Pd] (datasheet formula 7)

With minimal pcb surface area (theta J-A) is roughly 120degC/W (off the end of the chart, if the thermal pad underneath that adapter has no copper at all to solder to then it might be more like 150degC/W.

Assume voltage drop across the LDO is 3V and max load current is 40mA and ambient inside enclosure of 35degC (with a few salas shunts nearby it could easily be more than this)

Pd = 3*0.04 = 0.12W

Tjunction = 35+120*0.12 = 50degC

That's probably realistic for driving one mechanical relay. Arduino and LCD might be more like 300mA (at a guess here).

In that case ... Tjunction = 143degC

Datasheet recommends 125degC as max junction temp for highest expected ambient and highest expected load.

See now how qusp and Ian think you'll have another visit from that dreaded blue smoke monster that lives inside these chips? There is no need for his visit to be a surprise, all the info is in the datasheet

Last edited by hochopeper; 27th November 2012 at 11:49 PM.
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Old 27th November 2012, 11:49 PM   #289
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Quote:
Originally Posted by hochopeper View Post
If I were you I would have a read of the datasheet for power dissipation and look at the load currents that you're expecting. Consider that you're also driving LCD etc from arduino.

You should be able to calculate if you expect smoke or not

qusp, I think with Ian's pcb you might just be able to get to the power pad from underneath. Though it's surely not going to be an easy (I mean heating from underneath while keeping the chip straight?) or even a neat or reliable job without a rework station.


What are you using to supply the regulator anyway? Seems an odd choice for the non-critical parts of the circuit. Considering that the i2c will be isolated and the relays are ... well it just feels odd to drive the coil of a relay with something with performance like this.

hochopeper,

My TPS7A4700 PCB has a hole under the QFN20 thermal pad . So, it would be easier to solder the pad from back of the PCB even by a normal soldreing iron.

Although it rated at 1A, I don't think it can keep good low noise performance for a output greater than 200ma. So, I don't suggest for a high current application .

Ian
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Last edited by iancanada; 27th November 2012 at 11:52 PM.
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Old 27th November 2012, 11:58 PM   #290
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Originally Posted by iancanada View Post
hochopeper,

My TPS7A4700 PCB has a hole under the QFN20 thermal pad . So, it would be easier to solder the pad from back of the PCB even by a normal soldreing iron.

Although it rated at 1A, I don't think it can keep good low noise performance for a output greater than 200ma. So, I don't suggest for a high current application .

Ian

I thought I had seen that hole when looking at the prototype pcbs when you posted photos. I'm still not sure about getting a normal soldering iron to the other pads of the chip and producing a neat or reliable job on them. Maybe I'm just looking for any excuse to buy a new soldering station??


I agree with you on the recommended loads there. For an isolated micro controller and LCD display (all isolated from the audio electronics) I don't think we should worry too much about noise performance An LM317 would do everything needed.

Chris

Last edited by hochopeper; 28th November 2012 at 12:01 AM.
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