hello,
i have some question, someone told me if i have a separate power supply for VD and VA within one IC (say, CS4396), there will be a problem called "latch up" if the time for reaching max voltage is different.
what is it, and will this problem effect / damaged the IC?
i have some question, someone told me if i have a separate power supply for VD and VA within one IC (say, CS4396), there will be a problem called "latch up" if the time for reaching max voltage is different.
what is it, and will this problem effect / damaged the IC?
I cannot comment on the veracity of that claim, but latch-up usually occurs when there's a current flowing in the substrate (the part of the Si that all the IC is on). It's not normally damaging, but the part won't work at all when it happens (you'd need to cycle the power).
Use antiparallel diodes from each supply to the other. It will prevent latch up. Please use low Uf Schottky diodes.( BATxx series ).
Peter Daniel posted the schematic of Kusonoki's Version 3 DAC. If you search for that one you can see how it is done in that schematic if it is unclear what I say.
Latch-up occurs when the devices power lines behave differently ( i.e. one is slower than the other ) when switched on. Generally it causes a lock-up of the chip in question and it can cause damage with some chips. Symmetric power supplies with 78xx/79xx have the problem sometimes. The negative regulator comes in an undefined state then and most peculiar voltages can occur at it's outputs. Adding 4 diodes as described in the datasheets is an effective solution and good practice "just in case".
Peter Daniel posted the schematic of Kusonoki's Version 3 DAC. If you search for that one you can see how it is done in that schematic if it is unclear what I say.
Latch-up occurs when the devices power lines behave differently ( i.e. one is slower than the other ) when switched on. Generally it causes a lock-up of the chip in question and it can cause damage with some chips. Symmetric power supplies with 78xx/79xx have the problem sometimes. The negative regulator comes in an undefined state then and most peculiar voltages can occur at it's outputs. Adding 4 diodes as described in the datasheets is an effective solution and good practice "just in case".
In general, latch up is the phenomenon that a circuit gets stuck in some undesired stable bias point where it does not function as desired.
In IC's, there are usually parasitic thyristors (SCR's) between the supply and ground. When these get triggered, for example by incorrect power-up sequencing or by pushing excessive current spikes into the inputs, they short-circuit the supply, which is a very undesirable stable bias point. Unless the power supply has a low current limit, the IC may self-destruct in a couple of seconds.
In IC's, there are usually parasitic thyristors (SCR's) between the supply and ground. When these get triggered, for example by incorrect power-up sequencing or by pushing excessive current spikes into the inputs, they short-circuit the supply, which is a very undesirable stable bias point. Unless the power supply has a low current limit, the IC may self-destruct in a couple of seconds.
Yep. Some CMOS chips have that parasitic SCR as part of the output driver totem pole. Pull the output line a little above Vdd and you turn on that SCR and it crowbars the DC rail.MarcelvdG said:
My experience...
Hi,
I had a latchup problem with the CS4390 DAC last year.
The problem was due to earth currents which happened at switch-on, and caused some differential bounce of the 2 earth planes.
The 3 lessons I learned were:
1 Keep the earth planes as as low Z, and similar Z as possible.
2 Don't hang other "quiet" circuitry on the analogue supply, nor other "noisy" stuff on the digital supply.
3 Watch out for the total decoupling uF value, and make it the same for Va and Vd.
To show how you can be "right on the edge" of these things happening; I had built 4 identical units, with professional PTH pcb's and identical components. 2 Units displayed the symptom, whilst 2 didn't. Swapping chips did not affect it.
Cheers,
Hi,
I had a latchup problem with the CS4390 DAC last year.
The problem was due to earth currents which happened at switch-on, and caused some differential bounce of the 2 earth planes.
The 3 lessons I learned were:
1 Keep the earth planes as as low Z, and similar Z as possible.
2 Don't hang other "quiet" circuitry on the analogue supply, nor other "noisy" stuff on the digital supply.
3 Watch out for the total decoupling uF value, and make it the same for Va and Vd.
To show how you can be "right on the edge" of these things happening; I had built 4 identical units, with professional PTH pcb's and identical components. 2 Units displayed the symptom, whilst 2 didn't. Swapping chips did not affect it.
Cheers,
i am now testing and evaluating dir1703, but it dosnt work stablily, i use seperate power supply, and i dont know what happen , the IC always DIE! may be i need to try to use one power supply ...
and one more thing make me confuse... the filter use in data sheet and in EV board is different!
and one more thing make me confuse... the filter use in data sheet and in EV board is different!
Prmature death of DIR1703
Hi Takashi,
Did you provide the DIR1703 with 3.3V? 5V will blow it up.
Just a thought.😎
takashi said:
Hi Takashi,
Did you provide the DIR1703 with 3.3V? 5V will blow it up.
Just a thought.😎
hi, elso
i am sure it is 3.3V, i use lm1085-3.3 to provide the voltage.
and i use it with pcm1738/1730, but still have some problem on sound stage, i have done 2 phototype, the first one have good performance in sound stage, but dir1703 part not stable,
and the second board stable, but the sound stage have some problems, the sound cannot separate clearly, a little bit duty even though the background is very quite.
and under test with 10k sine wave and 20k sine wave, the analog output become triangular wave...(but the first board is a fine sine wave)
i dont know what happen, i still need to work hard on it~
i am sure it is 3.3V, i use lm1085-3.3 to provide the voltage.
and i use it with pcm1738/1730, but still have some problem on sound stage, i have done 2 phototype, the first one have good performance in sound stage, but dir1703 part not stable,
and the second board stable, but the sound stage have some problems, the sound cannot separate clearly, a little bit duty even though the background is very quite.
and under test with 10k sine wave and 20k sine wave, the analog output become triangular wave...(but the first board is a fine sine wave)
i dont know what happen, i still need to work hard on it~
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