LM7480-Q1: LM7480-Q1

Hi,

Thank you for the response. I am thinking the LM74930-Q1 is a part that will meet our needs.

Here is a question I hope you can answer:

In a previous version of this design I had a discrete bidirectional power switch followed by an eFuse, TPS2663x.

I want to be able to hot plug this device. Do you think the LM74930-Q1 can replace my discrete power switch and provide the same

functionality as the eFuse? The inportant features are reverse polarity protection, bidirectional current flow, hot plug capability.

Thanks,

Dan

Hi,

I may have misunderstood.

I want the LM74930-Q1 to operate as a bidirectional power switch.

I have the eval board and I noticed that if I remove the power supply at VIN and put a power supply on

VOUT and then enable the part there is no voltage at VIN. (RCB disabled)

I suspect the gate drivers do not work if there is no VIN.

I thought the RCB disable meant the part can be used as a bidirectional power switch.

Please clarify.

Thanks,

Dan

Hi Dante,

If VIN is not present, LM74930-Q1 will not function. It cannot be used as a bi-directional switch. It is true that we can disable RCB but powering up the IC without VIN is not achievable.

Regards,

Shiven Dhir

Is there anyway to make the part operate n a bidirectional mode?

Actually, there is a way to do this and I did it with the eval board.

Hi Dante, 

Can you elaborate more on how you achieved this.

Regards,

Shiven Dhir

I basically achieved this by diode-ORing on the Vs input and the UVLO input.

Please see the attached schematic of my design that incorporates these concepts.

I am including two schematic pages, one has the LM74930 and the other has the battery charger.

If you can review I would appreciate it.

Danbridge-schematic-rev6 - TI review.pdf

Hi Dante, 

I need to check with our designer if it is okay to use it like this.

On top level I can see that when VIN is not present:

VOUT is high which means UVLO will be high and VS is also high. Everything looks fine but "A" will never go high. Because of this DGATE will not turn on.

Just to summarize the requirement. We just need a bidirectional switch. Right?

Reverse polarity protection, reverse current blocking are not required.

Regards,

Shiven Dhir

Hi Shiven, Thanks for the response.

I can tell you this did work on the bench.

The requirements are:

1) Normal forward mode as the datasheet describes

2) Reverse mode where the board is sourcing power, so RCB must be off to allow current to flow out of the board.

I this mode I power Vs via the diode as shown and I set UVLO with a diode as shown.

Dan

Hi Dante, 

As you mentioned that this worked on bench.

Did you test under these conditions? VIN floating, VOUT ~12V. VS and UVLO high. I am unsure if your DGATE went high.

Since the underlined condition will not be completed first, DGATE shouldn't rise.

Also, do you also require current protection features? Like OCP,SCP.IMON

If not, LM74502-Q1 can achieve what you are looking for.

Regards,

Shiven Dhir

Hi,

DGATE does go high in the forward and reverse directions.

I did change the UVLO resistor string to accommodate my situation.

I had RCP disabled so current can flow in reverse.

I do want the protection features, specifically RPP.

Dan

Hi Dante,

DGATE might go high since RCB is disabled. Although in first start condition, if you only power up VOUT and VIN is floating DGATE will not power up as I mentioned. VA has its own PORR.

Also, if you want RPP specifically. Bidirectional RPP is not offered. 

Note: You can achieve a bi-directional switch with LM74502-Q1 where Input RPP is present. All the current specific protection features are not present.

Regards,

Shiven Dhir

Hi,

I'm not sure I understand the last response.

Please answer the following.

If you answers can be detailed it will help me understand.

If you'd like to refer me to another apps engineer that would be fine.

1) Did you review my schematic?

Please use the signal names in my schematic so I can understand what you are referring to.

Or if you are referring to the pin names on a part, please let me know.

2) When you say VIN is floating, what do you mean? I have diode D22 providing power to the VA input on the LM74930 for reverse operation.

3) When you say the LM74502 can be a bidir switch, do you mean I can do that with the diode OR-ing I have shown in my schematic?

4) Are you saying my schematic will not offer bidirectional RPP?

5) Can you explain the usage of the SW pin for the LM74930, right now I have it floating.

6) For UVLO operation I have two networks in my design. One for the forward direction and one for the reverse direction, is this correct?

Thank you,

Dan

Here is a summary of requirements that my customer requires, I hope this helps.

1) Forward operation, power supplied to my board from off the board

2) RPP in the forward direction, to protect the board for negative voltage surges

3) 2A current max in both directions

4) Need to withstand 150V surge, this is achieved with a TVS and the proper FET

5) The ability to turn on RCP with a pin (mode) on the chip is a nice feature for us, we control this with our onboard uP.

We want to be able to enable reverse operation and reverse current flow under uP control

6) We need to operate in reverse mode, this means we need to source power from our onboard battery to a device off the board

7) We do not need RPP when the board is sourcing power, RPP is only needed when power is delivered TO the board

8) 

Hi Dan,

1. I did review your schematic and I will explain with your schematic names now.

2. Let us consider a startup case. VOUT is 12V and VIN is floating. Which means it is the reverse direction startup. Here, VS has been taken care of. UVLO is also take care of.

But something to note here is, in first startup VA does not have any voltage and its VA(PORR) is not crossed.

3. You can achieve a bi-directional switch with LM74502-Q1 by changing the VS power as shown.

4. No, this will not offer bidirectional RPP and also damage the controller. When you apply negative voltage on VOUT, device is bound to get damaged.

5. SW pin is a voltage sensing pin of common source point and is controlled by EN. If this is not required, you can keep SW floating.

6. You have taken care of UVLO by ORing UVLO of VIN and VOUT. Which is fine.

Bi-directional RPP with ideal diodes are not designed because it is an ideal diode and is expected to survive negative voltage only on one side. If One side experience negative voltage, the other side is immune and hence reverse polarity protection is achieved.

Regards,

Shiven Dhir

Hi Dante,

Thanks for sharing requirements. All of this can be achieved in LM74502 (except #5).

Regards,

Shiven Dhir

Hi Dante,

Now I understand how you are planning to power up VA. This makes sense to me now. As output RPP is also not a requirement anymore, I believe this can be used. Let me check with our designer if there is a chance of violating any abs-max in this use case.

Regards,

Shiven Dhir

Hi,

Ok, let me know.

Can we communicate with email?

Yes, RPP is only needed in the forward direction.

Are those symbols in you response supposed to be diodes?

I will let SW float.

I like the simplicity of the LM74502, but I think the lack of the MODE pin is an issue as we want to turn on RCP at will.

Dan

Hi,

I tried to accept the friendship request, but there is nothing on the page the link sends me to

Hi Dante,

What is your operating voltage range? I see it is 28V nominal. Do you have any transients expected?

Regards,

Shiven Dhir