LM5177EVM-HP: LM5177 datasheet comparison with evaluation board for DC-DC backup operation

Hello Brigitte,

Thank you for your reply. The figure on page 50 of the datasheet. It has 4 control loops. 1) Internal peak current control loop, 2) Internal Vout (VSYS) control loop 3) Internal constant current loop 4) extrernal linear Vin (VBAT) CV Control.

In case of DC/DC back up operation. The first three control loops are implemented by LM5177 and only the fourth loop needs to be implemented. The the voltage at the battery can also be regulated during charging.

This is what I understood from the figure. Is my understanding correct?

Best Regards,

Mohsin Ejaz Ahmad

Just one more question regarding the design of an external voltage controller. Are there any recommended values of resistors and capacitors from TI for the external CV loop?

Regards,

Mohsin 

Hello Stefan,

Thank you for your answer. In the document that you have shared in Figure 4, the ourput should be V(comp) or V(mode)? Is it a typing error?

Regards,

Mohsin

Hello Mohsin,

have you read the whole document? It describes 2 different methods, one on COMP and one on the MODE pin.

Best regards,

 Stefan

Hello Stefan,

Yes, I have read the document. You are right that there are two methods. 

If you open the document and see the Figure 4 for COMP pin control. The output of that circuit is going to V(MODE). Should it be connected to V(MODE) or V(COMP)?

Similarly, in the figure 1, the external voltage controllers are for the storage side. But for hysteretic control V(BAT) is the input and for Linear control V(VIN) is the input. 

opposite to this the figure on page 50 to datasheet seems consistant that for both types of the controls the input is the V(BAT).

I think this document SNVAA69 is unconsistant and have typo errors that confuses the reader.

Best Regards,

Mohsin

Hello,

I am working with the evaluation board LM5177EVM-HP. I have changed the Feedback resistors (R1 and R2) to get the desired output voltage. Till at this point the board is working fine upto 165W output power.

As a next step, I have implemented the Reverse CV reuglation circuit that is mentioned in User's guide of LM5177 EM. 

Also for the monitoring of the input current, I have removed the jumper from the J11 connector to enable IMONOUT. 

Now there are some questions.

1. If I consider,  J1, J3 as the source input voltage and J2 and J4 as the battery terminals, then the current meausrement connections are reversed as mentioned in the datasheet of LM5177 on page 50. Moreover, I have tried the operation in this mode. It just works fine untill the input voltage goes upto the required voltage for the backup operation that is set by R53 and R54 in the Reverse CV regulation and the output becomes 3 times of the input voltage.

In my opionion, the reverse regulation should not have effect at this point and the input voltage should be allowed to vary from 4V to 36V like in normal operation.

Further, when I turn off the source voltage, the back-up operation does not work and the voltage across J1 and J3 becomes zero. It should set it to the reverse CV regulation voltage configuered with R53 and R54. 

2. If I now consider that at J1, J3 battery is connected and at J2 and J4 source is connected as mentioned in the data sheet and this https://www.ti.com/lit/pdf/snvaa69. It also does not work as the current measurements are not like in the datasheet page 50.

How can I work further with the evalution board to make it oiperational for DC back operation? 

Best Regards,

Mohsin Ejaz Ahmad

Hi Mohsin,

Stefan is out of office until Thursday, so a response from him will be delayed.
In the meantime, could you check the general design with the new output voltage with our quickstart calculator?
https://www.ti.com/tool/download/SNVR519
This way we can rule out any instabilities that may be caused due to a change in output voltage.

Thanks and best regards,
Niklas

Hello Niklas,

Thank you so much for the reply.

The document SNVR519 is quite helpful. I have read it before. 

I have one question: in the document the Compensation components are calculated and mentioned with Rc, Cc1 and Cc2 names (see the excel rows 87,88 and 89) but I cannot see these names in the diagram that is shown at the start of the excel sheet.

It will be nice from TI, if the labelling of the resistors, capacitors and the inductors remains the same atleast in one document. 

Moreover, i will wait for the reply from Stefan.

Best Regards,

Mohsin

Hi Mohsin,

Thanks for the notice and also thank you very much for your patience.

Stefan will get back to you before the end of this week.

Best regards,
Niklas

Hello Stefan,

Also, my query from Monday (last 3 days) is resolved. 

The demo board is now operating in the bidirectional or backup mode. I think it will be a good start for me for the next steps. Thank you for your support.

Best Regards,

Mohsin Ejaz Ahmad

Hello Stefan,

I have another question. I have reasd the Application Note "Dynamic Current Tracking With the LM5177 4-Switch Buck Boost Controller".

Is it possible to use this stated method in back-up applications? 

Or can I simply give a PWM of 500 kHz to at the DTRK pin to regulate the system side voltage?

Right now with the demo board I have set up the back-up system (as shown on page 50 of the LM5177 datasheet), I am not using ATRK/SS or DTRK pin. I am using ATRK/SS at the start of the operation for soft start. Becuase in case, the battery has to deliver power to the load e.g. 1 A load the battery side current reaches the maximum limit by increasing the capacitance at SS/ATRK pin, it takes longer to turn on but it resolves this problem of current saturation at the power ON by the battery side.

Therefore, till at this point LM5177 serves the back-up operation. 

I want to investigate further to control the system-side voltage somehow with the microcontroller or a DSP. (that is connected to the output of the LM5177).

As a first try, can I give an analog voltage at the SS/ATRK pin directly from an external source? because DTRK pin on Page 50 of datasheet is connected to the ground.

I am waiting for your reply.

Thank you so much.

Best Regards,

Mohsin Ejaz Ahmad

Hi Mohsin,

i am not sure if i understood all the points you mentioned above.

You can connect an analog signal to SS/ATRK and as long as this is below the Reference Voltage (Vref = 1V) this signal level will be used as reference instead and regulate the output voltage level.

The same can be done with feeding in a PWM at DTRK but 500kHz might be to low frequency.

Note: To stop the internal SS phase you can toggle the MODE pin so that the SS cap charging current will be disabled.

Best regards,

 Stefan

Hello Stefan,

Thank you for your reply and you understood me correctly.

So now my demo board is in back-up operation. I can set the system side or the output voltage with the DTRK pin. The PWM frequency I am using is of 2 MHz. But I think the operation will also work if I use 500 kHz as mentioned in the data sheet of LM5177.

This make the overall operation more stable. 

Thank you for your help. 

Best Regards,

Mohsin Ejaz Ahmad