INNO3977 Design

Hello Sarvesh,

If my understanding is correct, you would like to make your own transformer design using your own computations rather than our PI Expert tool right?

I would not recommend this because most of our device's, such as the INN3977CQ, uses ON/OFF control instead of PWM. Because of this, the main means of control for our IC is  different from other PWM devices so I would recommend using our PI Expert tool when designing a transformer that will be used with our devices. 

Please let me know if you have any follow-up questions.

Thanks for the reply. 

As I we need to have AEC qualified device,   I am going with INN3977CQ for my power level of 5W ( 15V, 0.167A & 15V& 0.17A- two outputs).

But, for the analysis at different loads, EP Switch have design Evaluation tab, but not with INN3977CQ part.

1. But, I got to know that INN3677 is equivalent part to INN3977CQ. Please let us know what all the parameters to be verified to say both are equivalant.

2. From the Design Evaluation page of INN3677EP, it is given that for my application, 

    Input: 100VDC-300VDC 

   Output : 1. 15V, 2.5W

                     2. 15V , 2.5W 

   Total output is 5W ( Two outputs)

   For this Duty ratio is from 2% to 18% ( deep DCM). I would like to understand, whether the device operate properly and have good regulation at this operating condition?

    

   3. And also frequency is going as low as 13kHz. How would I know when the device is operating in ON-OFF control & DCM like that.

Hi, 

Please reply above query soon please.

And I have one more query. From the Design Evaluation tool, I understand that the device works at fixed frequency with input variation ( Across the input range). 

But, operates at variable frequency with load( from no load to full load), right?

HI, 

I am awaiting the response for previous 2 queries. Requesting you to please response soon.

I have one more query.

This device working on variable frequency operation w.r.t. load. As the load reduces frequency reduces. And in my application the frequnecy is going as low as 14 kHz. 

As the frequency reduces, Bmax ( Max flux density will increase). But, how the device maintain the flux density without getting saturated? ( any duty ratio factor involved in this?)

Hello Sarvesh,

To answer your questions:

1. Some key things to take a look at to check if the two devices are equivalent in terms of operation are the current limit (standard and increased), the on-state resistance, max rated Vds stress, maximum on-time, and maximum switching frequency
2. The PI Expert design will issue warnings if there will be issues when operating. If the duty is too low, then the PI Expert will issue a warning. If there are no warnings, then the duty should be fine.
3. Our InnoSwitch3-EP and AQ devices are always under ON/OFF control regardless of switching frequency
4. The switching frequency varies for both different input voltage and output load. At constant output load, the switching frequency decreases as input voltage increases. At constant input voltage, the switching frequency increases as output load increases. Can you attach a link to the PI Expert design you used that generated the graph you sent. I would like to take a look at it and check . The one you attached previously is for the INN3977CQ.
5. The situation that you are stating where flux density increases with frequency reduction is for constant output load. As mentioned in 4 and in the graph you linked for this question, as load increases switching frequency also increases so the flux does not reach a point where the transformer will saturate.

Hi,

Thanks for the reply.

Design link with EP part: https://piexpertonline.power.com/piexpert/design/select?share=91da87998031728b86dc4ec2509f93da51db6210d49a1531854af8ce49ec08cf

Actually my design has 2 outputs. But, as the design evaluation is only for single output 15V, 5W is considered for singe output ( Output1: 15V, 2.5V & Output 2:  15V, 2.5W)

Design link for INN3977CQ: https://piexpertonline.power.com/piexpert/design/select?share=64de5d55d5319c44d0c653c4e6d08faeab12ddfa1be2c9f175c756c302f6b833

Queries:

1. From the characteristic device looks like operating in fixed frequency operation with input variation. Please see the Sec. 1 in the attachment

2. What is TIME_ON_MAX , TIME_ON_MIN and TIME_OFF ? TIME_OFF = (1-D) ? Please see the section2 screen shot in attachment

   Appreciate the quicker response.

   Have a good day!

   Thanks!

   Sarvesh

Hi,

Thanks for the reply.

Design link with EP part: https://piexpertonline.power.com/piexpert/design/select?share=91da87998031728b86dc4ec2509f93da51db6210d49a1531854af8ce49ec08cf

Actually my design has 2 outputs. But, as the design evaluation is only for single output 15V, 5W is considered for singe output ( Output1: 15V, 2.5V & Output 2:  15V, 2.5W)

Design link for INN3977CQ: https://piexpertonline.power.com/piexpert/design/select?share=64de5d55d5319c44d0c653c4e6d08faeab12ddfa1be2c9f175c756c302f6b833

Queries:

1. From the characteristic device looks like operating in fixed frequency operation with input variation. Please see the Sec. 1 in the attachment

2. What is TIME_ON_MAX , TIME_ON_MIN and TIME_OFF ? TIME_OFF = (1-D) ? Please see the section2 screen shot in attachment

   Appreciate the quicker response.

   Have a good day!

   Thanks!

   Sarvesh

Hi,

In the previous response it is stated that "Our InnoSwitch3-EP and AQ devices are always under ON/OFF control regardless of switching frequency".

I am reiterating my query again, As I was in the impression that device will operate CCM at high loads , valley switching DCM ( PWM control) at light loads  and ON/OFF control at very light loads. And also I was told that when < 25KHz device will operate in ON/OFF control and at higher frequency PWM control ( either CCM of valley switching DCM). Can you elaborate on this please?

Thanks!

Sarvesh.

Hello Sarvesh,

To answer your questions;

1. As I mentioned previously, the frequency varies by line voltage as well as load voltage. This is because our InnoSwitch varies the frequency, on-time, and off-time dynamically. I will also attach a couple of waveforms I took. The waveforms show the primary Vds waveform at constant output load but the input line is at 60V and 130V for each waveform. You can see that their frequency changed between the two conditions. The graph generated by PI XLS will need to be looked at. Thank you for bringing this to our attention. I will let our PI Expert team know and take a look at it.
2. The TIME_ON_MAX and TIME_ON_MIN are the maximum and minimum estimated on time of the primary switch. The TIME_OFF is the estimated minimum off time of the primary switch.  The duty cycle stated will not necessarily match since it is computed at a specific tolerance corner while TIME_ON_MAX/TIME_ON_MIN and TIME_OFF are ranges.
3. Let me clarify that the ON-OFF control mentioned is referring to the control scheme of our device while DCM/CCM is referring to the operating mode of the converter. Because of this whether the converter is operating at DCM or CCM, the InnoSwitch uses ON-OFF control.

I have a query regarding current limit.

In figure 6 of datasheet (innoswitch3-ep_family_datasheet-1145287.pdf) , it is given that Normalized current is getting less when teh load is reduced. Can we say current limit is reduced w.r.t. load?

If yes, then in the tool current limit is remained constant.

Please see the attached screen shot.

Thanks!

Sarvesh.

Hello Sarvesh,

You are correct in that the current limit decreases as load decreases. The graph generated from the tool will need to be looked at as well to check why it remains constant. I will bring this up with our PI Expert team as well. Thank you for bringing this to our attention.

Do we have simulation model to capture the stability analysis of INNO3977? 

Thanks!

Hi,

Please respond to my previous query.

Ands also it is given like " INN3977 is unconditionally stable". I hope to comment like this there wiuld be some documentation proof/ simulation or something. Please share teh link or doc related to stability.

Thanks!

Sarvesh.

Hello,

You can download a SIMPLIS model for the InnoSwitch here: SIMPLIS Model for InnoSwitch-3 | Power Integrations

Hi, I am mainly asking for stability analysis. As it is given in the document that " Inno switch is unconditionally stable", . Could you explain why it is unconditionally stable?

Please respond soon.

Regards,
Sarvesh

Hello,

You can see in our InnoSwitch3 designs that even with changes to input voltage and load, the converter remains stable. 

One design you can see this is this DER: DER-726 - 65 W Isolated Flyback Adapter Using InnoSwitch3-EP (750 V PowiGaN Switch) and MinE-CAP | Power Integrations

The transient response in particular is a  good indicator of stability.

If you are still unsure, you can run a simulation using our SIMPLIS model to run your design before a physical board power-up and check stability.     

Hi,

I am using INN3977CQ for my Flyback converter of 5W

Input Voltage = 100V to 300V

Out put1= 15V, 2.5V

Output2 = 15V, 2.5W.

To fit these 3 winding s we gone for E25/13/7 core and the design is attached here.

https://piexpertonline.power.com/piexpert/design/select?share=befc2db5935e35ef8eda913f1b5a734b8889662f79ffe794b73b24564b7bcbbd

I have a query regarding duty cycle.

@100V - Duty cycle is 0.106

@300V Duty cycle is 0.034

My serious concern the converter is operating from 3% to 10% duty cycle range only. I would like to understand, whether the converter regulates the output at this low duty cycle range.

 Could INN3977CQ could regulate the output with 3% duty cycle @ 300VDC input?

Please respond as soon as possible.

Regards,

Sarvesh

Hi,

INN3977 is working across wide inout range and wide output power range.

So, for a particular Input-Output condition, the duty ratio is fixed ( say for 100-300VDC input & 15V 5W out put D@100VinDC=0.108 D@300VinDC=0.034 from the tool). So , Xer is designed ccordingly. Am I correct?

Or can we increase the duty cycle to say, 0.45 @100VinDC somehow? If yes, please explain how to do that.

Regards,"
Sarvesh.

Hi,

INN3977 is working across wide inout range and wide output power range.

So, for a particular Input-Output condition, the duty ratio is fixed ( say for 100-300VDC input & 15V 5W out put D@100VinDC=0.108 D@300VinDC=0.034 from the tool). So , Xer is designed accordingly. Am I correct?

Or can we increase the duty cycle to say, 0.45 @100VinDC somehow? If yes, please explain how to do that.

Regards,"
Sarvesh.

Its almost a week awaiting the response. Please reply soon.

Thanks!

Please respond to my query. its been more than 2 weeks.

Please explain Why it is recommended to use Fail open capacitors for BPP pins of Innoswitch?