LM5176-Q1: CC and CV control

Hello Jeffrey,

1. Would you please explain or even better share measurements of the issue you observe? The first thing that comes to my mind is that the CV and CC controls need crossover frequencies that are not too close to each other, but I do not know if this is the case in your application.

2. To be honest, I do not have any idea how to control COMP with a digital signal without adding a filter before COMP.

3. I am not sure if I understand your question. I expect you ask for a software to control the voltage via a PWM signal on COMP, right?

Hi Brigitte,

1. Let me share the measurements of this issue with you.

2. Please explain "adding a filter before COMP" and recommend a filter.

3. Yes, I need a software(that can be used in MCU) or reference design guide to control the voltage via a PWM signal on COMP pin.

Regards,

Hello Jeffrey,

Please have a look at this reference design. The FB is controlled in this case, but I expect that the method should work as well when you apply it to COMP. You just need to recalculate the necessary values. A software example is there as well.

Hi Brigitte,

The measurement data you requested on previous post is attached below. I need your advice to resolve this issue. Please check it and let me know your solution.

LM5176-Q1_CC and CV control issue.pdf

Regards,

Hi Brigitte,

Thanks for your kind response. It will be help them to understand on CV and CC control of this device.

Regards,

Hi Brigitte,

Please check my customer's questions below and let me know that in more detail.

1. The output of Q37(LMV321) is 3.3V or 0V, so the output of LM5176 is turned off when the output of Q37 is 0V. What is the exact function of Q37(LMV321) and Q1(NCV124) circuit?

2. There is M_PWM_CC_CONTROL net on +IN pin of Q37. Please let me know how to control M_PWM_CC_CONTROL by MCU for CC control. Can it be controlled by PWM duty of MCU?

Regards

Hello Jeff,

Please tell me which schematic are these questions referring to?

Hi Brigitte,

You can refer to the attached schematic on 1st my post of this case. But I attached it again. Please refer to the attached schematic below.

1680.LM5176_Schematic.pdf

Regards,

Hello Jeffrey,

As this is the customer schematic, it is important that they check in detail if my assumptions are possible. This can be tested best with measurements on their board.

1. It looks to me as if this circuit informs the MCU if the output current is above or below a certain level (NCS214) and the signal going to the COMP pin (CC_LIMIT) increases or reduces the constant charge current. As far as I can see LMV321 is sending an analog signal dependent on the PWM from the MCU to the COMP pin to increase or reduce the DC level of this pin.

2. Yes, it looks as if this is a PWM signal creating a voltage to increase or reduce the level on the COMP pin.

Hi Brigitte,

Thanks for your kind explanation. I have two more questions below. Please check it and let me know.

1. I understood what you explained on previous post, but I'd like to ask you on the recommended PWM signal conditions. (for example, PWM frequency, PWM duty cycle, and so on) Should it be tested on their board?

2. There are schottky diode(SD1) and RC filters(R32/C74, R22/C95) in their schematic. I want to know that schottky diode must be needed or deleted or changed to other component. Also, I want to know that the values of RC filter must be tuned and tested by many measurements.

Regards,

Hello Jeff,

1. Yes this needs to be tested on their board, but as the PWM signal is used for driving an analog input, the RC filter used to their PWM signal indicates the minimum frequency necessary for a negligible ripple. The frequency should be high enough to get an analog signal with very small ripple after the RC filter.

2. RC filters can be calculated and the ripple estimated, so I expect that there is not a lot testing necessary. For the diode, please explain why you want to change it.

In general if the knowledge about the used circuit is no longer available, I recommend either not to touch the circuit or to do as much testing as necessary to understand the circuit in detail.

Hi Brigitte,

1. I understood theoretically as you explain on it. But I think it is very hard and difficult to be controlled by PWM signal, Could you recommend the technical guide documentation to test easily and to understand that control way? I couldn't find the technical guide in TI site and other site.

2. Because I just want to check that there are the problems on that circuit including the diode. There are no other reasons. That's it.

Thanks for your kind explanation. But it seems that I will ask you about this issue after that. I hope that you help me a lot.

Regards,

Hello Jeffrey,

1. Please review the data in this app note for how to create an analog signal with a digital PWM signal: 

In addition you might review the information in this article: 

Adjusting VOUT in USB Type-C™ and wireless charging applications, part 2

As I discussed in the first installment of this series , one option to control output voltage (V OUT ) for USB Type-C Power Delivery (PD) and wireless charging applications is to use switching resistors…

By Youhao Xi over 5 years ago in Technical articles > Power management

I would set the frequency 5 to 10 times higher than the frequency coming out of the RC time constant. And then you set the DC value by changing the duty cycle of the PWM signal.

2. I do not think that there is a problem with the diode, but for sure this needs to be tested over temperature.