TPS22965-Q1 Equation for ton,toff,tr,tf,tD

Hi Shinji,

Thank you for the detailed information. I have actually created a WEBENCH project with your parameters and found that the estimated rise time is 90.6us and the estimated fall time is 48us. These two timing parameters are important for most applications because the rise time can estimate the inrush current and the fall time estimates how long it will take to discharge the load capacitance. Is there a reason that the delay time, turn on time, and turn off time are needed?

Also, with such a small load the TPS22918-Q1 load switch can be used. Have you considered this device?

Thanks,

Alek Kaknevicius

Hi Alek,

Thank you for the response.

The delay time, turn on time and turn off time is required to see if meets proper power up/down sequence against other power rails.

Is there any way to estimate each value using an equation or webench?

Fall Time

TPS22965-Q1 has interanl QOD(quick output discharge) function using internal 225ohm resistor.

Is it included in the webench?

Rise Time

Could you also advise the min/typ/max tolerance of the rise time?

regards,

Hi Shinji,

We do not have any way to estimate the delay time, turn off time, or turn on time without measuring it (there is no equation or WEBENCH support for these parameters).

As for the fall time, WEBENCH incorporates both the load current and the QOD resistance (225Ω in this case).

Rise time will vary depending on process variation and temperature variation. While we do not provide min/max values for our timing parameters, you can expect a 50% shift as the temperature varies form -40C to 85C.

Would you be able to share your timing specifications with me so I can help come up with the appropriate solution? Are you looking for a CT capacitor value to see if you can stay within a certain timing window, or do you just want to see how long it will take your current solution to turn on/off?

Thanks,

Alek Kaknevicius

Thank you. I will check if the customer needs just how long does it take for the current solution or not.

By the way,
I found TINA TI model of TPS22965(non Q1) and try transient simulation.
It looks tr is much longer than the webench simulation.
Is there difference in tr between TPS22965 and TPS22965-Q1?

regards,

Hi Shinji,

While they are not exactly the same, they should be similar. Can you please provide an example of this? That way I can do some investigation and bring this up with the modeling team.

Thank you,

Alek Kaknevicius

Hi Alek,

Please see attached. TPS22965.xlsxTPS229651.xlsx

Hi Shinji,

Please find the data our group has taken for VIN=VBIAS=3.3V below:

VIN=VBIAS=3.3V, RL=10Ω, CL=0.1uF

CT Capacitor (pF)	tON (us)	tD (us)	tR (us)	tF (us)	tOFF (us)
0	231.3	139.7	215.7	3.363	9.270
220	641.7	361.0	636.0
470	1056.7	552.7	1096.7
1000	1653.3	810.0	1776.7
2200	4070.0	1823.3	4593.3
4700	8543.3	3796.7	9610.0
10000	17700.0	7723.3	20100.0

Based on the data, it looks like WEBENCH has the more accurate turn off behavior (fall time, turn off time) and TINA has the more accurate turn on behavior (turn on time, rise time, delay time). The measurements in the table above are from the Q1 version of this device.

Thanks,

Alek Kaknevicius

Hi Alek,

I would like to know if TINA-TI or Webench can be used to estimate the tr, tf, trise, tfall, td.

Could you measure the below customer condition and compare it against the Webench and TINA-TI?

ton, toff, tr, tf, tD

My condition is as below. 

Cin=100uF

Vin=VBIAS=3.3V

CT=0pF (NM)

CL=44uF

RL=110ohm

Von=3V

Hi Shinji,

I can collect this data on an EVM and will have it completed by either tomorrow (11/11) or Monday (11/14). Let me know if there are any other conditions you would like me to test.

Thanks,

Alek Kaknevicius

Hi Shinji,

I went down into the lab and took the requested data:

VIN=VBIAS=3.3V, CL=44uF, RL = 110ohms

tR	192us
tON	141us
tD	237us
tF	7.55ms
tOFF	3.598ms

Based on the data, it looks like TINA-TI is the more accurate source for this device.

Thanks,

Alek Kaknevicius

Hi Alek,

I have a question about your measurement data.

1. Ton doesn't match to TINA-TI result. Could you share your TINA-TI result?
2. It seems Tf also has some diffrenece.
3. Please make sure both TINA-TI model and your measured result reflect the 225ohm internal discharge path.          
4. Could you give me the worst case min/max variation of each data over Process/Temp(-40c to 105c) for the customer condition below?                                     

Vin（V）	Vbias（V)	Von(V)	Ct（nF)	Cout(uF)	RL(Ω)	Ton	Toff	Tr	Tf	Td
3.3	3.3	3	0	44uF	110Ω	330.8us	3.364ms	220.6us	10.58m	217.2us	TINA (Non Q1)
3.3	3.3	?	0	44uF	110Ω	141us （間違い？）	3.598ms	192us	7.55ms	237us	TI測定

Customer condition :

Cin=100uF

Vin=VBIAS=3.3V

CT=0pF (NM)

CL=44uF

RL=110ohm

Von=3V

Hi Shinji,

My apologies, the tON parameter and tD parameter are switched in the table I provided earlier. I typed that out incorrectly when I initially sent it. With that correction, it looks like the TINA model is slower than my measurements.

As for the fall time, we can use a bit of math to determine the "correct" fall time of the device. With a 110 ohm load and an internal QOD resistance of 225 ohms, the total resistance on the output is about 74 ohms. To discharge a 44uF capacitance down to 10% (0.33V), it would take about 7.5ms.

It looks like the TINA model does not take into account the QOD resistance, since a 110 ohm load would discharge the 44uF capacitance in about 11ms (as measured in TINA-TI). I will reach out to our modelling team to confirm.

I will email you separately about min/max timing.

Thanks,

Alek Kaknevicius