We have used TPS75333QPWP in a previous application and are looking at using it in a new application. However, the RESET timeout delay of 100ms is a little longer than we would prefer. Is there perhaps a similar part (voltage, current, etc.) that may have a shorter RESET timeout delay?
Hi Bob,
I would recommend trying out TPS74801 which has similar specs with a faster power-good signal.
Also, for reference here is a quick spec comparison between the two:
| TPS753 | TPS74801 | |
| Iout(Max)(A) | 1.5 | 1.5 |
| Vin(Max)(V) | 5.5 | 5.5 |
| Vin(Min)(V) | 2.7 | 0.8 |
| Vout(Max)(V) | 5 | 3.6 |
| Vout(Min)(V) | 1.5 | 0.8 |
| Fixed output options(V) | 1.8, 2.5, 3.3 | Adjustable |
| PSRR @ 100 KHz(dB) |
17 | 28 |
| Noise(uVrms) | 60 | 20 |
| Accuracy(%) | 2 | 2 |
| Dropout voltage (Vdo)(Typ)(mV) |
160 | 60 |
| Iq(Typ) (mA) |
0.075 | 1 |
| Output capacitor type | Non-Ceramic | Ceramic |
| Thermal resistance θJA(°C/W) |
43 | 44.2(VSON), 36(VQFN) |
| Operating temperature range(C) |
-40 to 125 | -40 to 125 |
| Package size: mm2 | 42 mm2: 6.4 x 6.5 (HTSSOP|20) | 25 mm2: 5 x 5 (VQFN|20), 9 mm2: 3 x 3 (VSON|10) |
| Packages | HTSSOP|20 | VQFN|20, VSON|10 |
Regards,
Andres
Hi Bob,
When using the soft start feature the startup time is calculated by: tss = (VREF × CNR/SS) / INR/SS, this sets the rise time for Vout. Here is a quick example using TPS7A8300:
This is taken from the Pros and Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator (ti.com) Application note, but this can be used to have a better picture. One can always use the total tss as a worst case in timing.
We can think of PG being a newer version of RESET, and for TPS748A, there is a typical spec for startup if no Css is used, therefore, if this 170us is used, then when Vout reaches 94% this would be ~160us, or if the 10nF spec is used then it would be~1.13ms
Best,
Edgar Acosta
Hi Bob,
The 1.13ms timing is related to the TPS748A and not the picture shown. That is for the TPS7A83, and it was to demonstrate how PG triggers once Vout reaches ~90% of its set value. I apologize if this caused any confusion.
So PG will assert high once Vout reaches a certain value and typically it is close to 90% of the set value, it could be 3.3V as in your case. The ISS current will not vary, this is a constant value that is always used for the soft start circuit. This allows to adjust the startup time by just placing an external capacitor.
So staying with the previous 10nF example, it will take Vout 1.2ms to reach its 3.3V. When Vout reaches ~2.97 V (90%), this will then translate to ~1.13ms in which PG will assert high. The rise of PG is independent of all this and it should rise quick almost as a step. Having said that, 2.3V is ~69.69% of 3.3V, this should be at ~0.836ms, giving an approximate window of 1.13ms-0.836ms~0.2940ms from 2.3V to the point when PG triggers.
Here is an example using the TPS74801 model:
Notice that Vout~3.3V and VPG rises at ~90% :
It takes Vout ~1.2ms to reach 3.3V and PG rises at ~1.07ms.
If we now look at the difference from 2.3V to the point where PG rises we see a difference of 0.239ms
Now, the simulation is not perfect and will have some inaccuracies, but overall it gives us close enough estimations and it shows the behavior of PG.
Best,
Edgar Acosta
Hi Bob,
I found some data on the Iss spec, and it seems that it doesn't deviate much from the 7.5uA, meaning that the accuracy is very tight, however, I have reached out to the team to confirm this and make sure that the data I am looking is also accross temp.
In regards your second question, correct me if I am wrong, but is seems you are asking for Load Regulation or Power Dissipation? Can you elaborate more what you mean by Iout varying with input and output voltage? If it is the Load Regulation then Figure 6-14 shows this:
If it is Power Dissipation, then this will also depend on the PCB layout and load, but the output current should not vary with input and output voltage. It could impact on how much headroom is needed, meaning that it will determine your dropout voltage.
If that is the case then at maximum current 1.5A, Vout of 1V, you would need a Vin of ~1.135V, or a 1.5V to provide more than sufficient headroom and keeping a decent power dissipation.
However, if thermals is the concern then, assuming standard JEDEC numbers, max Load and 5.25V worst case and continuous operation , Pd=6.375W, which is quite a lot of power dissipation. This corresponds to a 300C rise, which would trigger Thermal Shutdown immediately.
With the given conditions, lets assume maximum ambient temperature, Ta=125C, then Tj~150C with a power dissipation of 0.5W, therefore, Iout should not exceed ~0.1176 A. This is at the edge of operating at the maximum recommended temperature which would put the device close to thermal shutdown but still in a safe area to prevent overheating and damaging the part.
If Ta=25C, to reach a Tj of 125C, then Pd~2.2558, meaning Iout~0.53A
Let me know if this is what you were looking for.
Best,
Edgar Acosta
Can we use any of the TPS748 data with the TPS748A? As an example, the TPS748 has a formula for the feedback resistor values and a table for certain common voltages, but the TPS748A does not? If we can't use the TPS748 data that is missing from TPS48A, where would we find that data (without having to bother you) 
